![978-1-491-96699-0
[FILL IN]
Learning Swift 3
by Paris Buttfield-Addison , Jon Manning , and Tim Nugent
Copyright © 2016 Secret Lab. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc. , 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are
also available for most titles ( http://safaribooksonline.com ). For more information, contact our corporate/
institutional sales department: 800-998-9938 or corporate@oreilly.com .
Editor: Rachel Roumeliotis
Production Editor: FILL IN PRODUCTION EDI‐
TOR
Copyeditor: FILL IN COPYEDITOR
Proofreader: FILL IN PROOFREADER
Indexer: FILL IN INDEXER
Interior Designer: David Futato
Cover Designer: Karen Montgomery
Illustrator: Rebecca Demarest
January -4712: First Edition
Revision History for the First Edition
2016-12-05: First Early Release
See http://oreilly.com/catalog/errata.csp?isbn=9781491966990 for release details.
The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. Learning Swift 3, the cover image, and
related trade dress are trademarks of O’Reilly Media, Inc.
While the publisher and the author(s) have used good faith efforts to ensure that the information and
instructions contained in this work are accurate, the publisher and the author(s) disclaim all responsibil‐
ity for errors or omissions, including without limitation responsibility for damages resulting from the use
of or reliance on this work. Use of the information and instructions contained in this work is at your own
risk. If any code samples or other technology this work contains or describes is subject to open source
licenses or the intellectual property rights of others, it is your responsibility to ensure that your use
thereof complies with such licenses and/or rights.](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-8-320.jpg)
![11. Images and Deletion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Adding Attachments 327
Adding Image Attachments 329
Viewing Attachments 335
Deleting Attachments 346
Conclusion 353
12. Supporting the iOS Ecosystem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
Sharing with UIActivityController 355
Handoffs 358
Searchability 363
Conclusion 365
13. Extending iOS Apps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Searching with a Spotlight Indexing Extension 368
Conclusion 378
14. Multimedia and Location attachments]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
Audio Attachments 379
Video Attachments 392
Location Attachment 400
Conclusion 404
15. Polishing the iOS App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Opening Links in SFSafariViewController 405
3D Touch 409
Home Screen Quick Actions 410
Peek and Pop 413
Settings 414
Undo Support 416
Images with Filters 419
Worldwide Apps 423
Internationalization 424
Localization 427
Accessibility 432
Splitscreen Multitasking 437
Conclusion 438
Table of Contents | vii](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-13-320.jpg)
![Gärtner’s work on hybridisation had been preceded by other
enquiries into the same subject, those namely of Knight mentioned
above at the beginning of the century, and Herbert’s more ample
investigations published in his work on Amaryllideae in 1837. Gärtner
did not neglect to compare his observations at all points with the
results of his predecessors, especially those of Koelreuter, and he
deduced from the astonishing mass of material a number of general
propositions respecting the conditions under which the production of
hybrids is possible, the results of crossing, and the causes of failure.
A special interest attaches to his mixed and compound hybrids, to
his experiments on the various degrees of influence which foreign
pollen exercises on the behaviour of the female organ, and the
connection of this point with the formation of varieties. It is
impossible to give a more distinct account of Gärtner’s results
without entering into discussions which would exceed the limits of a
historical survey. It is the less necessary to do so, since Nägeli
undertook in 1865 to give a summary view of all the important
results to be found in the wealth of material supplied by Koelreuter,
Herbert and Gärtner[112]. Gärtner’s experiments in hybridisation
were conducted at Calw in Würtemberg, the place where Koelreuter
had made his in 1762 and 1763. And thus it was in two small cities
of Würtemberg that the foundations of the sexual theory were laid
and the theory itself perfected, as far as it could be by experiment
only, by three of the most eminent among observers. Camerarius in
Tübingen, Koelreuter and K. F. Gärtner in Calw contributed so largely
to the empirical establishment of the theory, that all that was done
by others would seem of small importance, if artificial pollination
only were in question. But Koelreuter was imperfectly acquainted
with the methods by which pollination is usually effected in nature;
Sprengel was the first who saw into all their more important
relations, and the fact must not be concealed, that Gärtner in
regarding Konrad Sprengel’s observations as unworthy of serious
consideration, neglected the most fruitful source of new and
magnificent results. His careful study of the secreting of nectar and
of the sensitiveness of the organs of fertilisation, and his many](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-51-320.jpg)
![observations on other biological relations in flowers, would have
found their natural termination, if he had connected them at all
points with Sprengel’s general conclusions respecting the relation of
the structure of the flower to the insect world. This Gärtner entirely
failed to do, and hence in this case also it was reserved for Darwin’s
wonderful talent for combination to sum up the product of the
investigations of a hundred years, and to blend Koelreuter’s,
Knight’s, Herbert’s, and Gärtner’s results with Sprengel’s theory of
flowers into a living whole in such a manner, that now all the
physiological arrangements in the flower have become intelligible
both in their relations to fertilisation, and in their dependence on the
natural conditions under which pollination takes place without the
aid of man. Here, as in morphology and systematic botany, Darwin
found the premisses given and drew the conclusion from them; here
too the certainty of his theory rests on the results of the best
observers, on investigations which find in that theory their necessary
logical and historical consummation.
7. Microscopic investigation into the processes of fertilisation in
the phanerogams; pollen-tube and egg-cells
[113]. 1830-1850.
Those who were convinced of the sexuality of plants had
endeavoured as early as the previous century to form some idea
with the help of the microscope of the way in which the pollen
effects the formation of the embryo in the ovule. We may pass over
Morland’s and Geoffroy’s very rude attempts in this direction:
Needham (1750), Jussieu, Linnaeus, Gleichen, and Hedwig imagined
that the pollen-grain bursts upon the stigma, and that the granules it
contains make their way downwards through the style to the ovules,
and are there either hatched into embryos or assist in their
production. This way of conceiving the matter was closely connected
with the theory of evolution which then prevailed, and seemed to
find some countenance in the seed-corpuscles of animals; it was also
supported by the observation that pollen-grains placed under the
microscope in water often burst and discharge their contents in the](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-52-320.jpg)
![Gleichen took the stomata, Koelreuter the indusium, Hedwig even
the glandular hairs of Ferns for anthers. It was not yet suspected
that the course of development and the whole morphology of the
Cryptogams could not be so compared with that of the
Phanerogams; correct and incorrect assumptions with regard to the
sexual organs of the Cryptogams were alike devoid of scientific
value, being mere guesses and vague conjectures. Nor was the state
of things much better even in the first years of the 19th century; and
if by that time a number of occasional observations had been made
which could afterwards be turned to scientific account, these were
as yet only isolated facts without scientific connection, and every
one was at liberty to concede or to refuse sexual organs to the
Cryptogams generally at his own discretion. Meanwhile observations
gradually accumulated, and towards 1845 it began to be possible by
critical examination of them to arrive at something like a clearer
understanding of this part of botany. The majority of botanists
readily accepted Schmidel’s and Hedwig’s opinion with respect to the
Mosses; Vaucher had as early as 1803 maintained that the long-
known conjugation of Spirogyra was a sexual act; Ehrenberg
observed in 1820 the conjugation of a Mould, Syzygites; Bischoff and
Mirbel explained the organisation of the antheridia of the Liverworts
in 1845, while Nees von Esenbeck saw the spermatozoids of
Sphagnum in 1822 and Bischoff those of Chara in 1828, though they
were at first taken for Infusoria, an opinion maintained by Unger as
late as 1834. But it was Unger[114], who in 1837, after careful study
of the spermatozoids of the Mosses in 1837, declared them to be the
male organs of fertilisation; in 1844 Nägeli discovered corresponding
forms on the prothallium of Ferns, which had till then been called a
cotyledon, and in 1846 the spermatozoids of Pilularia, the products
of the small spores which Schleiden had explained to be the pollen-
grains of that plant.
These facts were of the highest importance, but little was to be
made of them as long as the female organ in the plants in question,
the Mosses excepted, was unknown, and meanwhile it was only the
resemblance between vegetable and animal spermatozoids which led](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-58-320.jpg)
![The processes of development before and after fertilisation were
now cleared up by all these discoveries, but the direct observation of
the act of fertilisation was still wanting. Hofmeister (‘Flora,’ 1857, p.
122) describes the state of affairs in the following terms: ‘While
numerous investigations had thrown a clear light on the character of
the male and female organs, and on the way in which the embryo is
formed by repeated division of the egg-cell present before
fertilisation, we continued quite in the dark respecting the particular
nature of the fertilisation. Observation and experiment had
established the fact, that the influence of the spermatozoids on the
archegonia was required to produce an embryo in the latter. Female
moss-plants[115] separated from the male, macrospores in the
Vascular Cryptogams separated from the microspores, had in all
cases proved unproductive; but it was not even certainly known to
what point in the female organ the spermatozoids force their way. It
is true that Lesczyc and after him Mercklin had seen the entry of
moving spermatozoids into the mouth of archegonia in Ferns; but
Lesczyc’s account of the part which he supposed them to play there
afterwards, was proved to be an illusion. I had myself observed
motionless spermatozoids halfway down the neck of archegonia of
an Equisetum; but nothing was to be learnt of the manner in which
the spermatozoid affects the egg-cell. Then it happened that in the
spring of 1851, being engaged in observing the development of the
organs of vegetation of Ferns, I repeatedly saw spermatozoids
moving about in the basilar cells which enclose the egg-cell in the
archegonia of Ferns, and the majority of them even playing about
the egg-cell. Their movements were put an end to during the
observation by the commencement of changes, which the contents
of young vegetable cells which have been cut open usually
experience under the prolonged influence of water.’ Later
observations leave no doubt now that in the Muscineae and Ferns
single spermatozoids force their way into the naked egg-cell of the
archegonium.
The question was first set at rest in the Algae, where the process
of fertilisation could be seen directly and without exposing the](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-61-320.jpg)
![2. First inductive experiments and opening of new points of view in
the History of the Theory of the Nutrition of Plants.
All that Aristotle and his school, Cesalpino not excepted, are able
to tell us about the phenomena of vegetable life, was the result of
the most every-day observations, none of which were critically and
exactly tested to ascertain their actual correctness, while the larger
part of their physiological axioms were not derived from observations
on plants at all, but from philosophical principles, and especially from
analogies taken from the animal world.
The first step towards a scientific treatment of the doctrine of
nutrition was an enlargement and critical examination of the
materials to be gained from experience; nor were any difficult
observations or experiments needed to discover contradictions
between the truths of nature and the old philosophy; all that was
necessary was to look into things more closely and to judge of them
with less prejudice.
In this way Jung was led to oppose one important point of the
Aristotelian account of nutrition. In the second fragment of his work
‘De plantis doxoscopiae physicae minores’ is to be found a remark,
which is evidently directed against the notion that plants receive
their food already elaborated from the earth, and therefore give off
no excrements[116]. Plants, says Jung in accord with Aristotle,
appear not to need a thinking soul (anima intelligente), which would
be able to distinguish wholesome from unwholesome food, and
Aristotle therefore provided them with food which had already been
perfectly prepared in the earth. But Jung takes another view
founded on actual observation. It is very possible, he says, that the
openings in the roots which take in liquid matter are so organised,
that they do not allow every kind of juice to enter, and who can say
that plants have the peculiarity of only absorbing what is useful to
them, for like all other living creatures they have their excreta, which
are exhaled through the leaves, flowers, and fruits. But among these
he reckons the resins and other exuding liquids, and says that it is](https://image.slidesharecdn.com/91354-250319114103-3b23a6cd/85/Learning-Swift-3-Early-release-3rd-Edition-Jonathan-Manning-73-320.jpg)
Learning Swift 3 Early release 3rd Edition Jonathan Manning
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- 7. Jon Manning, Paris Buttfield-Addison, and Tim Nugent Learning Swift 3 Boston Farnham Sebastopol Tokyo Beijing Boston Farnham Sebastopol Tokyo Beijing
- 8. 978-1-491-96699-0 [FILL IN] Learning Swift 3 by Paris Buttfield-Addison , Jon Manning , and Tim Nugent Copyright © 2016 Secret Lab. All rights reserved. Printed in the United States of America. Published by O’Reilly Media, Inc. , 1005 Gravenstein Highway North, Sebastopol, CA 95472. O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles ( http://safaribooksonline.com ). For more information, contact our corporate/ institutional sales department: 800-998-9938 or [email protected] . Editor: Rachel Roumeliotis Production Editor: FILL IN PRODUCTION EDI‐ TOR Copyeditor: FILL IN COPYEDITOR Proofreader: FILL IN PROOFREADER Indexer: FILL IN INDEXER Interior Designer: David Futato Cover Designer: Karen Montgomery Illustrator: Rebecca Demarest January -4712: First Edition Revision History for the First Edition 2016-12-05: First Early Release See http://oreilly.com/catalog/errata.csp?isbn=9781491966990 for release details. The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. Learning Swift 3, the cover image, and related trade dress are trademarks of O’Reilly Media, Inc. While the publisher and the author(s) have used good faith efforts to ensure that the information and instructions contained in this work are accurate, the publisher and the author(s) disclaim all responsibil‐ ity for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any code samples or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights.
- 9. Table of Contents Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Part I. Swift Basics 1. Getting Started. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The Apple Developer Program 5 Registering for the Apple Developer Program 6 Downloading Xcode 7 Creating Your First Project with Xcode 8 The Xcode Interface 12 Developing a Simple Swift Application 20 Designing the Interface 21 Connecting the Code 22 Using the iOS Simulator 24 Conclusion 26 2. The Basics of Swift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 The Swift Programming Language 28 Swift 2 Versus Swift 3 30 Playgrounds 31 Comments 32 Variables and Constants 33 Operators 34 Control Flow 35 Loops 36 Switches 37 Types 40 iii
- 10. Working with Strings 40 Comparing Strings 41 Searching Strings 42 Optional Types 42 Type Casting 44 Tuples 45 Arrays 46 Dictionaries 48 Enumerations 48 Sets 50 Functions and Closures 51 Using Functions as Variables 54 Closures 56 The defer Keyword 58 The guard Keyword 58 Making your code Swifty 59 Conclusion 59 3. Swift for Object-Oriented App Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Classes and Objects 61 Initialization and Deinitialization 63 Properties 64 Inheritance 64 Protocols 68 Extensions 69 Access Control 70 Operator Overloading 72 Generics 73 Subscripts 74 Structures 75 Modules 76 The Swift Standard Library, Foundation, Cocoa, and Cocoa Touch 76 Swift Package Manager 77 Data 79 Loading Data from Files and URLs 79 Serialization and Deserialization 80 Error Handling 81 Memory Management 84 Design Patterns in Cocoa and Cocoa Touch 85 Model-View-Controller 85 Delegation 87 Structuring an App 89 iv | Table of Contents
- 11. The Application Delegate 89 Window Controllers and View Controllers 89 Nibs and Storyboards 90 Conclusion 90 Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Part II. An OS X App 4. Setting Up the OS X Notes App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Designing the OS X Notes App 124 Creating the OS X Project 127 Defining a Document Type 132 Adding the Icon 136 Conclusion 138 5. Working with Documents on OS X. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 The NSDocument Class 139 Storing Data in the Document 140 Storing Text 141 Package File Formats 142 The guard Keyword, and Why It’s Great 147 Saving Files 148 Loading Files 151 A Basic UI 154 Conclusion 162 6. User Interfaces and iCloud. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Updating the UI 163 Document-Filetype-Extension UI 167 Getting an Icon for the Collection View Cells 172 Adding Attachments 174 Storing and Managing Attachments 182 Displaying Data in the Collection View 190 Enhancing Attachments 193 Opening Attachments 193 JSON Attachments 197 Adding Attachments via Drag-and-Drop 202 Adding QuickLook 207 iCloud 213 The Basics of iCloud 214 Table of Contents | v
- 12. Conclusion 217 Part III. An iOS App 7. Setting Up the iOS Notes App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Designing the iOS Notes App 222 Creating the iOS Project 228 Enabling the iOS App for iCloud 232 Defining a Document Type 236 Conclusion 238 8. Working with Files in iCloud. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 The App Sandbox 239 iCloud Availability 241 Creating the Document List View Controller 242 View Controllers and Storyboards 244 The Navigation Controller 244 Collection Views 248 Using Constraints to Control Size and Position 250 Creating the Document Class 254 Listing Documents 260 Creating Documents 270 Downloading from iCloud 272 Deleting Documents 276 Renaming Documents 283 Conclusion 286 9. Working with Documents on iOS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Adding a View to Display Notes 289 Editing and Saving Documents 297 Conclusion 299 10. Working with Files and File Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Setting Up the Interface for Attachments 301 Listing Attachments 305 Determining Types of Attachments 307 Displaying Attachment Cells 310 Dealing with Conflicts 316 Creating the Quick Look Thumbnail 322 Conclusion 325 vi | Table of Contents
- 13. 11. Images and Deletion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 Adding Attachments 327 Adding Image Attachments 329 Viewing Attachments 335 Deleting Attachments 346 Conclusion 353 12. Supporting the iOS Ecosystem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 Sharing with UIActivityController 355 Handoffs 358 Searchability 363 Conclusion 365 13. Extending iOS Apps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 Searching with a Spotlight Indexing Extension 368 Conclusion 378 14. Multimedia and Location attachments]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 Audio Attachments 379 Video Attachments 392 Location Attachment 400 Conclusion 404 15. Polishing the iOS App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 Opening Links in SFSafariViewController 405 3D Touch 409 Home Screen Quick Actions 410 Peek and Pop 413 Settings 414 Undo Support 416 Images with Filters 419 Worldwide Apps 423 Internationalization 424 Localization 427 Accessibility 432 Splitscreen Multitasking 437 Conclusion 438 Table of Contents | vii
- 14. Part IV. Extending Your Apps 16. Building a watchOS App. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 Designing for the Watch 442 Designing Our watchOS App 444 Creating the watchOS Extension 446 Communicating with the iPhone 450 User Interfaces for the Apple Watch 469 Showing Note Contents 475 Creating New Notes 482 Adding Handoff Between the Watch and the iPhone 485 Glances 490 Conclusion 494 17. Code Quality and Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495 Debugging 495 Instruments 498 Testing 503 Unit Testing 504 UI Testing 506 Using Objective-C and Swift in the Same Project 508 Using Swift Objects in Objective-C 508 Using Objective-C Objects in Swift 509 The App Store 510 App Thinning 511 Testing iOS Apps with TestFlight 512 Conclusion 513 viii | Table of Contents
- 15. Preface Welcome to Learning Swift 3! This book will help you put the Swift programming language into practice by walking you through the development of a note-taking application for the Apple iOS, OS X, and watchOS platforms. Swift is a pretty amazing modern language, taking the best from other newer lan‐ guages without reinventing the wheel. Swift is easy to write, easy to read, and really hard to make mistakes in. Our philosophy is that the best way to learn Swift is to build apps using it! To build apps, though, you need a great framework, and Apple has several: Cocoa, Cocoa Touch, and WatchKit, to name only a few. This book could quite easily be titled Learning Cocoa and Cocoa Touch with Swift, or something similar, because the frame‐ works are just as important as the language itself. At the time of writing, Swift is cur‐ rently at version 3, and has a bright future ahead of it. Resources Used in This Book We recommend following the book by writing code yourself as you progress through each chapter. If you get stuck, or just want to archive a copy of the code, you can find what you need via our website. As this book teaches you how to build a real-world app, we primarily focus on show‐ ing you the coding side of things. We’re not going to ask you to paint your own icons, so we’ve provided them for you. You can also download them from our website. Audience and Approach This book is solely focused on Swift 3 and does not cover the use of Objective-C. We might mention it occasionally, but we don’t expect you to know how to use it. We first cover the basics of the Swift 3 language, and then move on to teach as much of the language as we can, as well as the use of the Cocoa, Cocoa Touch, and watchOS ix
- 16. frameworks, through the construction of a complete app for both OS X and iOS. As a reminder, Swift is the programming language, Cocoa is the framework for OS X apps, Cocoa Touch is the framework for iOS apps, and somewhat predictably, watchOS is the framework for the Apple Watch. This book’s approach differs from that of other programming books that you may have encountered. As we’ve mentioned, we believe that the best way to learn Swift is to build apps using it. We assume that you’re a reasonably capable programmer, but we don’t assume you’ve ever developed for iOS or OS X, or used Swift or Objective-C before. We also assume that you’re fairly comfortable navigating OS X and iOS as a user. Organization of This Book In this book, we’ll be talking about Cocoa and Cocoa Touch, the frameworks used on OS X and iOS, respectively. Along the way, we’ll also be covering Swift, including its syntax and features. In Part I, Swift Basics, we begin with a look at the tools used for programming with Swift, as well as the Apple Developer Program. Then we move on to the basics of the Swift programming language and structuring a program for Apple’s platforms, as well as common design patterns. Chapter 1 covers the basics of Apple’s developer program, and guides you through a simple Swift app. Chapter 2 explores all the basics of Swift, and prepares you for using it to build more complex applications. Chapter 3 discusses Swift’s object-oriented features, as well as the structure of a good app. In Part II, An OS X App, we build a simple note-taking application for Macs, target‐ ing OS X. Along the way, we discuss the design of the app, how it’s structured, how it uses documents, and how to build all the features. Chapter 4 starts off our OS X notes app, and sets up the document model, and icon. Chapter 5 goes into detail on working with documents in OS X apps. Chapter 6 connects the app to iCloud, and finishes up the OS X app. In Part III, An iOS App, we build a fully featured iOS note-taking application as a companion for the OS X app from Part II. Chapter 7 starts off our iOS app, and sets up the same document model for iOS. Chapter 8 connects the iOS app to iCloud. x | Preface
- 17. Chapter 9 creates an interface on iOS for displaying our notes. Chapter 10 sets up the iOS app to handle attachments. Chapter 11 adds image support to the iOS app. Chapter 12 adds sharing and searching support to the iOS app. Chapter 13 adds a today widget to the iOS app. Chapter 14 adds location, audio, video, and contact attachments to the iOS app, as well as notifications. Chapter 15 finishes the iOS app with a whole lot of polish! In Part IV, Extending Your Apps, we add a watchOS app, and explore bug hunting and performance tuning. Chapter 16 adds a watchOS app to the iOS app, allowing for Apple Watch support. Chapter 17 explores debugging and performance tuning. Conventions Used in This Book The following typographical conventions are used in this book: Italic Indicates new terms, URLs, email addresses, filenames, and file extensions. Constant width Used for program listings, as well as within paragraphs to refer to program ele‐ ments such as variable or function names, databases, data types, environment variables, statements, and keywords. Constant width bold Shows commands or other text that should be typed literally by the user. Constant width italic Shows text that should be replaced with user-supplied values or by values deter‐ mined by context. This element signifies a tip or suggestion. Preface | xi
- 18. This element signifies a general note. This element indicates a warning or caution. Using Code Examples Supplemental material (code examples, exercises, errata, etc.) is available for down‐ load at our website. This book is here to help you get your job done. In general, if example code is offered with this book, you may use it in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a signifi‐ cant amount of example code from this book into your product’s documentation does require permission. We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “Learning Swift by Jonathon Man‐ ning, Paris Buttfield-Addison, and Tim Nugent (O’Reilly). Copyright 2016 Secret Lab, 978-1-491-94074-7.” If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [email protected]. Safari® Books Online Safari Books Online is an on-demand digital library that deliv‐ ers expert content in both book and video form from the world’s leading authors in technology and business. Technology professionals, software developers, web designers, and business and crea‐ tive professionals use Safari Books Online as their primary resource for research, problem solving, learning, and certification training. xii | Preface
- 19. Safari Books Online offers a range of plans and pricing for enterprise, government, education, and individuals. Members have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kauf‐ mann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and hundreds more. For more information about Safari Books Online, please visit us online. How to Contact Us Please address comments and questions concerning this book to the publisher: O’Reilly Media, Inc. 1005 Gravenstein Highway North Sebastopol, CA 95472 800-998-9938 (in the United States or Canada) 707-829-0515 (international or local) 707-829-0104 (fax) We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at http://bit.ly/learning-swift. To comment or ask technical questions about this book, send email to bookques‐ [email protected]. For more information about our books, courses, conferences, and news, see our web‐ site at http://www.oreilly.com. Find us on Facebook: http://facebook.com/oreilly Follow us on Twitter: http://twitter.com/oreillymedia Watch us on YouTube: http://www.youtube.com/oreillymedia Acknowledgments Jon thanks his mother, father, and the rest of his crazily extended family for their tre‐ mendous support. Paris thanks his mother, without whom he wouldn’t be doing anything nearly as interesting, let alone writing books. Tim thanks his parents and family for putting up with his rather lackluster approach to life. Preface | xiii
- 20. We’d all like to thank our editors, Rachel Roumeliotis and Brian MacDonald—their skill and advice were invaluable to completing the book. Likewise, all the O’Reilly Media staff we’ve interacted with over the course of writing the book have been the absolute gurus of their fields. A huge thank you to Tony Gray and the Apple University Consortium (AUC) for the monumental boost they gave us and others listed on this page. We wouldn’t be writ‐ ing this book if it weren’t for them. And now you’re writing books, too, Tony—sorry about that! Thanks also to Neal Goldstein, who deserves full credit and/or blame for getting us into the whole book-writing racket. We’re thankful for the support of the goons at MacLab (who know who they are and continue to stand watch for Admiral Dolphin’s inevitable apotheosis), as well as pro‐ fessor Christopher Lueg, Dr. Leonie Ellis, and the rest of the staff at the University of Tasmania for putting up with us. “Apologies” to Mark Pesce. He knows why. Additional thanks to Rex S., Nic W., Andrew B., Jess L., and Ash J., for a wide variety of reasons. And very special thanks to Steve Jobs, without whom this book (and many others like it) would not have reason to exist. Thanks also to our tech reviewers, with special thanks to Chris Devers and Tony Gray for their thoroughness and professionalism. Finally, thank you very much for buying our book—we appreciate it! And if you have any feedback, please let us know. You can email us at [email protected] and find us on Twitter @thesecretlab. xiv | Preface
- 23. CHAPTER 1 Getting Started This book is a work-in-progress. We will be releasing regular Early Release editions, with a final version late in 2016. The book may be inconsistent, out of date, or incomplete until then. Please let us know if you have any feedback by emailing learningswift@secret‐ lab.com.au This book teaches the Swift 3 programming language by exploring the development of three applications for Apple platforms: OS X, iOS, and watchOS. This book’s approach might differ from what you’re used to, because our philosophy is that the best way to learn Swift is to build apps using it! The vast majority of the code in this book will be part of the apps we’re building—a full note-taking app for OS X, iOS, and watchOS—rather than individual pieces of sample code. You can see the final product in Figure 1-1. 3
- 24. Figure 1-1. Our finished app, for OS X, iOS, and watchOS Our app is fully functional, but we do make some deliberate design and feature deci‐ sions along the way to constrain the scope a little (the book is more than 500 pages!). As we mentioned in the preface, we assume that you’re a reasonably capable pro‐ grammer, but we don’t assume you’ve ever developed for iOS or OS X, or used Swift or Objective-C before. We also assume that you’re fairly comfortable navigating OS X and iOS as a user. We recommend that you work through this book front to back, building the OS X app, then the iOS app, then the watchOS app, even if you’re only interested in one of the platforms. By approach‐ ing the book this way, you’ll get the best understanding of what building a real app with Swift requires. Programming with Swift, and using the Cocoa and Cocoa Touch frameworks to develop OS X and iOS apps, respectively, involves using a set of tools developed by Apple. In this chapter, you’ll learn about these tools, where to get them, how to use them, how they work together, and what they can do. At the end of this chapter, you’ll make a very simple Swift application for iOS, before we dive into the details of the Swift language and Apple’s frameworks in the following two chapters. 4 | Chapter 1: Getting Started
- 25. The Apple development tools have a long and storied history. Orig‐ inally a set of standalone application tools for the NeXTSTEP OS, they were eventually adopted by Apple for use as the official OS X tools. Later, Apple largely consolidated them into one application, known as Xcode, though some of the applications (such as Instru‐ ments and the iOS simulator) remain somewhat separate, owing to their relatively peripheral role in the development process. You’ll notice the prefix NS on many of the classes you use for Cocoa and Cocoa Touch development with Swift. This prefix comes from the NeXTSTEP heritage of many of Apple’s frameworks. In addition to the development tools, Apple offers developers a paid membership in its Developer Program, which provides resources and support. The program allows access to online developer forums and specialized technical support for those interes‐ ted in talking to the framework engineers. If you are just interested in learning Swift and exploring the development tools, you can do so for free. You will need a paid membership, however, if you wish to use developer services like iCloud in your apps, or to distribute anything you build through either the iOS or OS X App Store. Swift is open source, but this doesn’t really mean much when it comes to using it to develop apps for OS X, iOS, and watchOS. There’s an excellent community of people working on the language that you can find at the Swift website. With the introduction of Apple’s curated App Stores for OS X, iOS, and watchOS, as well as emerging Apple platforms like tvOS, the Developer Program has become the official way for developers to provide their credentials when submitting applications to Apple—in essence, it is your ticket to selling apps through Apple. In this chapter, you’ll learn how to sign up for the Apple Developer Program, as well as how to use Xcode, the development tool used to build apps in Swift. The Apple Developer Program The paid Apple Developer Program provides access to beta development tools, beta operating system releases, and distribution ability through Apple’s App Stores. It also allows you to use some of the cloud-dependent features of the platforms, such as iCloud, CloudKit, In-App Purchase, Maps, and App Groups. We will be using a lot of cloud-dependent features, including Maps and iCloud, in the apps we build throughout this book. You will not be able to run these apps if you do not have a paid member‐ ship. The Apple Developer Program | 5
- 26. It isn’t necessary to be a member of the Apple Developer Program if you don’t intend to submit apps to the App Stores, or don’t need the cloud-dependent features. We strongly recommend joining, though, if you intend to build apps for any of Apple’s platforms, as the other benefits are substantial: • Access to the Apple Developer Forums, which are frequented by Apple engineers and designed to allow you to ask questions of your fellow developers and the people who wrote the OS. • Access to beta versions of the OS before they are released to the public, which enables you to test your applications on the next version of the OS X, iOS, watchOS, and tvOS platforms, and make necessary changes ahead of time. You also receive beta versions of the development tools. • A digital signing certificate (one for each platform) used to identify you to the App Stores. Without this, you cannot submit apps to the App Store, making a membership mandatory for anyone who wants to release software either for free or for sale via an App Store. That said, registering for the Developer Program isn’t necessary to view the docu‐ mentation or to download the current version of the developer tools, so you can play around with writing apps without opening your wallet. Registering for the Apple Developer Program To register for the Developer Program, you’ll first need an Apple ID. It’s quite likely that you already have one, as the majority of Apple’s online services require one to identify you. If you’ve ever used iCloud, the iTunes store (for music or apps), or Apple’s support and repair service, you already have an ID. You might even have more than one (one of this book’s authors has four). If you don’t yet have an ID, you’ll create one as part of the registration process. When you register for the Developer Program, the membership gets added to your Apple ID. If you don’t want to register for the paid developer program, you can skip to “Downloading Xcode” on page 7 for instructions on installing Xcode, the developer tools. Once again, keep in mind that you won’t be able to build the apps that we teach in this book if you don’t have a paid membership, as we use cloud-dependent features such as iCloud and Maps. There are alternatives to many of Apple’s tools—such as the Google Maps SDK for iOS, or cloud-storage services from Amazon and Microsoft. However, you’ll still need a paid membership through Apple to put apps in the iTunes App Store. 6 | Chapter 1: Getting Started
- 27. Once you’re on the Apple Developer Program website, simply click Enroll, and follow the steps to enroll. You can choose to register as an individual or as a company. If you register as an indi‐ vidual, your apps will be sold under your name. If you register as a company, your apps will be sold under your company’s legal name. Choose carefully, as it’s very diffi‐ cult to convince Apple to change your program’s type. If you’re registering as an individual, you’ll just need your credit card. If you’re regis‐ tering as a company, you’ll need your credit card as well as documentation that proves you have authority to bind your company to Apple’s terms and conditions. For information on code signing and using Xcode to test and run your apps on your own physical devices, see Apple’s App Distribu‐ tion Guide. We don’t cover this in the book, as it’s a process that changes often. Apple usually takes about 24 hours to activate an account for individuals, and longer for companies. Once you’ve received confirmation from Apple, you’ll be emailed a link to activate your account; when that’s done, you’re a full-fledged developer! Downloading Xcode To develop apps for either platform, you’ll use Xcode, Apple’s integrated development environment. Xcode combines a source code editor, debugger, compiler, profiler, iOS simulator, Apple Watch simulator, and more into one package. It’s where you’ll spend the majority of your time when developing applications. At the time of writing, Xcode is only available for Mac, but who knows what the future holds for the iPad Pro? You can get Xcode from the Mac App Store. Simply open the App Store application and search for “Xcode,” and it’ll pop up. It’s a free download, though it’s rather large (several gigabytes at the time of writing). Once you’ve downloaded Xcode, it’s straightforward enough to install it. The Mac App Store gives you an application that on first launch sets up everything you need to use Xcode. Just launch the downloaded app, and follow the prompts, and you’ll be up and running in no time. The Apple Developer Program | 7
- 28. This book covers Swift 3, which is available only if you’re using Xcode 7 or later. Make sure you’re using the latest version of Xcode from the Mac App Store. It’s good practice to use the latest Xcode at all times. Creating Your First Project with Xcode Xcode is designed around a single window. Each of your projects will have one win‐ dow, which adapts to show what you’re working on. To start exploring Xcode, you’ll first need to create a project by following these steps: 1. Launch Xcode. You can find it by opening Spotlight (by pressing ⌘-space bar) and typing Xcode. You can also find it by opening the Finder, going to your hard drive, and opening the Applications directory. If you had any projects open previ‐ ously, Xcode will open them for you. Otherwise, the Welcome to Xcode screen appears (see Figure 1-2). Figure 1-2. The Welcome to Xcode screen 2. Create a new project by clicking “Create a new Xcode project” or go to File→New→Project. You’ll be asked what kind of application to create. The template selector is divi‐ ded into two areas. On the lefthand side, you’ll find a collection of application categories. You can choose to create an iOS, watchOS, or OS X application from the project templates, which will set up a project directory to get you started. 8 | Chapter 1: Getting Started
- 29. Because we’re just poking around Xcode at the moment, it doesn’t really matter what we select, so choose Application under the iOS header and select Single View Application. This creates an empty iOS application and displays the project settings window shown in Figure 1-3. Figure 1-3. The project settings window 3. Name the application. Enter HelloSwift in the Product Name section. 4. Enter information about the project. Depending on the kind of project template you select, you’ll be asked to provide different information about how the new project should be configured. At a minimum, you’ll be asked for the following information, no matter which platform and template you choose: The product’s name This is the name of the project and is visible to the user. You can change this later. Your organization’s name This is the name of your company or group. It’s not directly used by Xcode, but new source code files that you create will mention it. Creating Your First Project with Xcode | 9
- 30. Your organization identifier This is used to generate a bundle ID, a string that looks like a reverse domain name (e.g., if O’Reilly made an application named MyUsefulApplication, the bundle ID would be com.oreilly.MyUsefulApplication). Bundle IDs are the unique identifier for an application, and are used to identify that app to the system and to the App Store. Because each bundle ID must be unique, the same ID can’t be used for more than one application in either of the iOS or Mac App Stores. That’s why the for‐ mat is based on domain names—if you own the site use‐ fulsoftware.com, all of your bundle IDs would begin with com.usefulsoftware, and you won’t accidentally use a bun‐ dle ID that someone else is using or wants to use because nobody else owns the same domain name. If you don’t have a domain name, enter anything you like, as long as it looks like a backward domain name (e.g., com.mycompany will work). If you plan on releasing your app, either to the App Store or elsewhere, it’s very important to use a company identi‐ fier that matches a domain name you own. The App Store requires it, and the fact that the operating system uses the bundle ID that it generates from the company identifier means that using a domain name that you own eliminates the possibility of accidentally creating a bundle ID that conflicts with someone else’s. If you’re writing an application for the Mac App Store, you’ll also be prompted for the App Store category (whether it’s a game, an educational app, a social net‐ working app, or something else). Depending on the template, you may also be asked for other information (e.g., the file extension for your documents if you are creating a document-aware application, such as a Mac app). You’ll also be asked which language you want to use; because this book is about Swift, you should probably choose Swift! The additional information needed for this project is covered in the following steps. 5. Make the application run on the iPhone by choosing iPhone from the Devices drop-down list. 10 | Chapter 1: Getting Started
- 31. iOS applications can run on the iPad, iPhone, or both. Appli‐ cations that run on both are called “universal” applications and run the same binary but have different user interfaces. For this exercise, just choose iPhone. You should be building universal iOS apps, in general, and we’ll be doing that when we properly start on iOS, in Part III. 6. Leave the rest of the settings as shown in Figure 1-4. Click Next to create the project. Figure 1-4. The project settings 7. Choose where to save the project. Select a location that suits you. We recommend putting all your work related to this book (and other Swift programming learning you might do) in one folder. You might notice a little checkbox for Source Con‐ trol; this creates a source code control repository for your code, giving you a place where you can save and manage different versions of your code as you cre‐ ate them. While in general this is a good idea to use, for this example project, make sure this is unchecked. Once you’ve done this, Xcode will open the project, and you can now start using the entire Xcode interface, as shown in Figure 1-5. Creating Your First Project with Xcode | 11
- 32. Figure 1-5. The entire Xcode interface The Xcode Interface As mentioned, Xcode shows your entire project in a single window, which is divided into a number of sections. You can open and close each section at will, depending on what you want to see. Let’s take a look at each of these sections and examine what they do. The editor The Xcode editor (Figure 1-6) is where you’ll be spending most of your time. All source code editing, interface design, and project configuration take place in this sec‐ tion of the application, which changes depending on which file you have open. If you’re editing source code, the editor is a text editor, with code completion, syntax highlighting, and all the usual features that developers have come to expect from an integrated development environment. If you’re modifying a user interface, the editor becomes a visual editor, allowing you to drag around the components of your inter‐ face. Other kinds of files have their own specialized editors as well. When you first create a project, the editor will start by showing the project settings, as seen in Figure 1-6. 12 | Chapter 1: Getting Started
- 33. Figure 1-6. Xcode’s editor, showing the project settings The editor can also be split into a main editor and an assistant editor through the edi‐ tor selector. The assistant shows files that are related to the file open in the main edi‐ tor. It will continue to show files that have a relationship to whatever is open, even if you open different files. For example, if you open an interface file and then open the assistant, the assistant will, by default, show related code for the interface you’re editing. If you open another interface file, the assistant will show the code for the newly opened files. At the top of the editor, you’ll find the jump bar. The jump bar lets you quickly jump from the content that you’re editing to another piece of related content, such as a file in the same folder. The jump bar is a fast way to navigate your project. The toolbar The Xcode toolbar (Figure 1-7) acts as mission control for the entire interface. It’s the only part of Xcode that doesn’t significantly change as you develop your applications, and it serves as the place where you can control what your code is doing. Figure 1-7. Xcode’s toolbar From left to right, after the OS X window controls, the toolbar features the following items: Run button (Figure 1-8) Clicking this button instructs Xcode to compile and run the application. Creating Your First Project with Xcode | 13
- 34. Figure 1-8. The Run button Depending on the kind of application you’re running and your currently selected settings, this button will have different effects: • If you’re creating a Mac application, the new app will appear in the Dock and will run on your machine. • If you’re creating an iOS application, the new app will launch in either the iOS simulator or on a connected iOS device, such as an iPhone or iPad. Additionally, if you click and hold this button, you can change it from Run to another action, such as Test, Profile, or Analyze. The Test action runs any unit tests that you have set up; the Profile action runs the application Instru‐ ments (we cover this much later, in Chapter 17); and the Analyze action checks your code and points out potential problems and bugs. Stop button (Figure 1-9) Clicking this button stops any task that Xcode is currently doing—if it’s building your application, it stops; and if your application is running in the debugger, it quits it. 14 | Chapter 1: Getting Started
- 35. Figure 1-9. The stop button Scheme selector (Figure 1-10) Schemes are what Xcode calls build configurations—that is, what’s being built, how, and where it will run (i.e., on your computer or on a connected device). Figure 1-10. The scheme selector Projects can have multiple apps inside them. When you use the scheme selector, you choose which app, or target, to build. To select a target, click on the left hand side of the scheme selector. You can also choose where the application will run. If you are building a Mac application, you will almost always want to run the application on your Mac. If you’re building an iOS application, however, you have the option of running the application on an iPhone simulator or an iPad simulator. (These are in fact the same application; it simply changes shape depending on the scheme that you’ve selected.) You can also choose to run the application on a connected iOS device if it has been set up for development. Creating Your First Project with Xcode | 15
- 36. Status display (Figure 1-11) The status display shows what Xcode is doing—building your application, down‐ loading documentation, installing an application on an iOS device, and so on. Figure 1-11. The status display If there is more than one task in progress, a small button will appear on the left hand side, which cycles through the current tasks when clicked. Editor selector (Figure 1-12) The editor selector determines how the editor is laid out. You can choose to dis‐ play either a single editor, the editor with the assistant, or the versions editor, which allows you to compare different versions of a file if you’re using a revision control system like Git or Subversion. Figure 1-12. The editor selector We don’t have anywhere near the space needed to talk about using version control in your projects in this book, but it’s an important topic. We recommend Jon Loeliger and Matthew McCullough’s Version Control with Git, 2nd Edition (O’Reilly). View selector (Figure 1-13) The view selector controls whether the navigator, debug, and utility panes appear on screen. If you’re pressed for screen space or simply want less clutter, you can quickly summon and dismiss these parts of the screen by clicking each of the elements. 16 | Chapter 1: Getting Started
- 37. Figure 1-13. The view selector The navigator The lefthand side of the Xcode window is the navigator, which presents information about your project (Figure 1-14). Figure 1-14. The navigator pane has eight tabs at the top The navigator is divided into eight tabs, from left to right: Creating Your First Project with Xcode | 17
- 38. Project navigator Lists all the files that make up your project. This is the most commonly used nav‐ igator, as it determines what is shown in the editor. Whatever is selected in the project navigator is opened in the editor. Symbol navigator Lists all the classes and functions that exist in your project. If you’re looking for a quick summary of a class or want to jump directly to a method in that class, the symbol navigator is a handy tool. Search navigator Allows you to perform searches across your project if you’re looking for specific text. (The shortcut is ⌘-Shift-F. Press ⌘-F to search the current open document.) Issue navigator Lists all the problems that Xcode has noticed in your code. This includes warn‐ ings, compilation errors, and issues that the built-in code analyzer has spotted. Test navigator Shows all the unit tests associated with your project. Unit tests used to be an optional component of Xcode but are now built into Xcode directly. Unit tests are discussed much later, in “Unit Testing” on page 504. Debug navigator Activated when you’re debugging a program, and it allows you to examine the state of the various threads that make up your program. Breakpoint navigator Lists all of the breakpoints that you’ve set for use while debugging. Report navigator Lists all the activity that Xcode has done with your project (such as building, debugging, and analyzing). You can go back and view previous build reports from earlier in your Xcode session, too. Utilities The utilities pane (Figure 1-15) shows additional information related to what you’re doing in the editor. If you’re editing a Swift source file, for example, the utilities pane allows you to view and modify settings for that file. 18 | Chapter 1: Getting Started
- 39. Figure 1-15. The utilities pane, showing information for a source file Creating Your First Project with Xcode | 19
- 40. The utilities pane is split into two sections: the inspector, which shows extra details and settings for the selected item; and the library, which is a collection of items that you can add to your project. The inspector and the library are most heavily used when you’re building user interfaces; however, the library also contains a number of useful items, such as file templates and code snippets, which you can drag and drop into place. The debug area The debug area (Figure 1-16) shows information reported by the debugger when the program is running. Whenever you want to see what the application is reporting while running, you can view it in the debug area. By default the debug area is not shown unless there is a program running. You can bring up the debug area by using the Xcode Toolbar View selector middle button. Figure 1-16. The debug area The area is split into two sections: the left hand side shows the values of local vari‐ ables when the application is paused; the right hand side shows the ongoing log from the debugger, which includes any logging that comes from the debugged application. You can show or hide the debug area by clicking on the view selector, at the top right of the window (see Figure 1-17). Figure 1-17. The central button in the view selector, which hides and shows the debug area Developing a Simple Swift Application Through the bulk of this book, we’ll be developing a complex, full-fledged Swift application, spanning three of Apple’s platforms: OS X, iOS, and watchOS. But for now, before we even explore how and why Swift itself works, we’re going to get a brief taste by building a very, very simple application for iOS. 20 | Chapter 1: Getting Started
- 41. If you’re more interested in Mac development, don’t worry! Exactly the same techniques apply, and we’ll be exploring Mac apps in detail later on, in Part II. This simple application is extremely cutting-edge: it will display a single button that, when tapped, will pop up an alert and change the button’s label to “Test!” We’re going to build on the project we created earlier in “Creating Your First Project with Xcode” on page 8, so make sure you have that project open. It’s generally good practice to create the interface first and then add code. This means that your code is written with an understanding of how it maps to what the user sees. To that end, we’ll start by designing the interface for the application. Designing the Interface When building an application’s interface using Cocoa and Cocoa Touch, you have two options. You can either design your application’s screens in a storyboard, which shows how all the screens link together, or you can design each screen in isolation. As a general rule, storyboards are a better way to create your interfaces even if you only have a single view, as in the case of this first application we are building. The reason is that if you later want to give your application more than one view, it will be easier to do that in a storyboard. Start by opening the interface file and adding a button. These are the steps you’ll need to follow: 1. First, we’ll need to open the main storyboard. Because newly created projects use storyboards by default, your app’s interface is stored in the Main.storyboard file. Open it by selecting Main.storyboard in the project navigator. The editor will change to show the application’s single, blank frame. You may need to pan or zoom the view around in order to fit it on your monitor. 2. Next, we need to drag in a button. We’re going to add a single button to the frame. All user interface controls are kept in the Object library, which is at the bottom of the utilities pane on the right hand side of the screen. To find the button, you can either scroll through the list until you find Button, or type button in the search field at the bottom of the library. Once you’ve located it, drag it into the frame. 3. At this point, we need to configure the button. Every item that you add to an interface can be configured. For now, we’ll change only the text on the button. Developing a Simple Swift Application | 21
- 42. Select the new button by clicking it, and select the Attributes Inspector, which is the third tab from the right at the top of the utilities pane. You can also reach it by pressing ⌘-Option-4. There are many attributes on the button; look for the one labeled Title. The Title attribute has two different components inside of it, a drop-down box and a text field containing the text “Button.” In the text field, change the button’s Title to “Hello!” You can also change the button’s title by double-clicking it in the interface. Our simple interface is now complete (Figure 1-18). The only thing left to do is to connect it to code. Figure 1-18. Our completed simple interface Connecting the Code Applications aren’t just interfaces—as a developer, you also need to write code. To work with the interface you’ve designed, you need to create connections between your code and your interface. There are two kinds of connections that you can make: 22 | Chapter 1: Getting Started
- 43. • Outlets are variables that refer to objects in the interface. Using outlets, you can instruct a button to change color or size, or to hide itself. There are also outlet collections, which allow you to create an array of outlets and choose which objects it contains in the interface builder. • Actions are methods in your code that are run in response to the user interacting with an object. These interactions include the user touching a finger to an object, dragging a finger, and so on. To make the application behave as we’ve just described—tapping the button displays a label and changes the button’s text—we’ll need to use both an outlet and an action. The action will run when the button is tapped, and will use the outlet connection to the button to modify its label. To create actions and outlets, you need to have both the interface builder and its cor‐ responding code open. Then hold down the Control key and drag from an object in the interface builder to your code (or to another object in the interface builder, if you want to make a connection between two objects in your interface). We’ll now create the necessary connections: 1. First, open the assistant by selecting the second button in the editor selector in the toolbar. The symbol is two interlocking circles. The assistant should open and show the corresponding code for the interface ViewController.swift. If it doesn’t, click the intertwining circles icon (which repre‐ sents the assistant) inside the jump bar and navigate to Automatic→View‐ Controller.swift. Make sure you don’t select the assistant symbol in the toolbar, as that will close the assistant editor. 2. Create the button’s outlet. Hold down the Control key and drag from the button into the space below the first { in the code. A pop-up window will appear. Leave everything as the default, but change the Name to helloButton. Click Connect. A new line of code will appear: Xcode has created the connection for you, which appears in your code as a property in your class: @IBOutlet weak var helloButton : UIButton 3. Create the button’s action. Hold down the Control key, and again drag from the button into the space below the line of code we just created. A pop-up window will again appear. This time, change the Connection from Outlet to Action, set the Name to showA lert, and click Connect. Developing a Simple Swift Application | 23
- 44. More code will appear. Xcode has created the connection, which is a method inside the ViewController class: @IBAction func showAlert(sender: AnyObject) { } 4. In the showAlert method you just created, add in the new code: var alert = UIAlertController(title: "Hello!", message: "Hello, world!", preferredStyle: UIAlertControllerStyle.Alert) alert.addAction(UIAlertAction(title: "Close", style: UIAlertActionStyle.Default, handler: nil)) self.presentViewController(alert, animated: true, completion: nil) self.helloButton.setTitle("Test!", forState: UIControlState.Normal) This code does the following things: It creates a UIAlertController, which displays a message to the user in a pop-up window. It prepares it by setting its title to “Hello!” and the text inside the window to “Hello, world!” Finally, an action that dismisses the alert is added, with the text “Close”. The alert is then shown to the user. Finally, it sets the title of the button to “Test!” The application is now ready to run. Click the Run button in the upper-left cor‐ ner. The application will launch in the iPhone simulator. Don’t worry if the app takes a while to launch the first time; the simulator can take a fair amount of time on first launch. If you happen to have an iPhone or iPad connected to your com‐ puter, Xcode will try to launch the application on the device rather than in the simulator. To make Xcode use the simulator, go to the Scheme menu in the upper-left corner of the window and change the selected scheme to the simulator. When the app finishes launching in the simulator, tap the button. An alert will appear; when you close it, you’ll notice that the button’s text has changed. Using the iOS Simulator The iOS simulator (Figure 1-19) allows you to test out iOS applications without hav‐ ing to use actual devices. It’s a useful tool, but keep in mind that the simulator behaves very differently compared to a real device. 24 | Chapter 1: Getting Started
- 45. Figure 1-19. The iOS simulator For one thing, the simulator is a lot faster than a real device and has a lot more mem‐ ory. That’s because the simulator makes use of your computer’s resources—if your Mac has 8 GB of RAM, so will the simulator and if you’re building a processor- intensive application, it will run much more smoothly on the simulator than on a real device. The iOS simulator can simulate many different kinds of devices: everything from the iPad 2 to the latest iPad Pro, and from the Retina display 3.5- and 4-inch iPhone- Using the iOS Simulator | 25
- 46. sized devices to the latest 4.7-inch and 5.5-inch iPhones. It can also test on variable size devices. To change the device, open the Hardware menu, choose Device, and select the device you want to simulate. You can also change which simulator to use via the scheme selector in Xcode. Each simulator device is unique, and they do not share informa‐ tion. So if you want to test your application on different simulators, you will need to build it again through Xcode. If you change hardware in the simulator while running an app, it will crash and Xcode will alert you. Be wary of changing the hard‐ ware in the simulator while testing applications unless you really like crashes. You can also simulate hardware events, such as the home button being pressed or the iPhone being locked. To simulate pressing the home button, you can either choose Hardware→Home, or press ⌘-Shift-H. To lock the device, press ⌘-L or choose Hard‐ ware→Lock. There are a number of additional features in the simulator, which we’ll examine more closely as they become relevant to the various parts of iOS we’ll be discussing. Conclusion In this chapter, we’ve looked at the basics of the Apple Developer Program, as well as the tools used for building apps. We’ve also made a really quick and simple iOS app, just to give you a taste of the process. In the next two chapters, we’ll look at the Swift programming language, using a feature of Xcode and Swift called Playgrounds to work with Swift code outside of the application context. 26 | Chapter 1: Getting Started
- 47. CHAPTER 2 The Basics of Swift This book is a work-in-progress. We will be releasing regular Early Release editions, with a final version late in 2016. The book may be inconsistent, out of date, or incomplete until then. Please let us know if you have any feedback by emailing learningswift@secret‐ lab.com.au The Swift programming language was first introduced in June 2014 at Apple’s World‐ wide Developers Conference (WWDC). Swift was a surprise to everyone: Apple had managed to develop an entire language (as well as all of the supporting libraries, developer tools, and documentation) and make it work seamlessly with the existing Objective-C language. And on top of that, it was a really good “1.0” language. In June 2015, Apple announced Swift 2.0, improving the performance of the lan‐ guage, adding a collection of new features, and making the Cocoa and Cocoa Touch platform APIs more Swift-like in style. Swift was open sourced on December 3, 2015 and is now as much a community run project as it is run by Apple. We can expect Swift to evolve over time, in line with the developments in the Swift Open Source project. Xcode supports having multiple versions of the Swift language installed. You might have a different version of the language if, for example, you’ve downloaded a copy of Swift from the open source project. For information on how to get a copy and use it in Xcode, go to the Swift project’s Download page. This book covers Swift 3, which was released in September 13 2016. The 3.0 release was a very big deal in the Swift community and included numerous changes to the language as well as to the standard library. With the release of Swift 3 future changes 27
- 48. to the language aim to be smaller in scope and with greater support of backwards compatibility in mind. If you have older Swift code that you need to update to the latest stable Swift syntax, Xcode provides a converter. Open the Edit menu and choose Convert→To Latest Swift Syntax… to get started. Swift draws upon an extensive history of language design and has a number of very cool design features that make developing software easier, simpler, and safer. We’ll begin this chapter with a high-level overview of what Swift aims to do, and how it sets about doing it, before we dive into the details of the language. As Swift develops, it’s likely that some of the syntax that we use in this book will become out of date, or change (as is true for any pro‐ gramming book). We’ll keep the book’s page on our site up to date with a changelog for the latest Swift for as long as we’re able. In this chapter, you’ll learn the basics of coding in Swift 3.0, which was released in September 2016. The Swift Programming Language The Swift programming language has the following goals: Safety Swift is designed to be a safe language. Many of the pitfalls of C, such as acciden‐ tally working with null pointers, are much harder to encounter. Swift is very strongly typed, and objects aren’t allowed to be null except under very specific circumstances. Modernity Swift contains a large number of modern language features designed to make it easy to express the logic of your code. These include pattern-matching switch statements (see “Switches” on page 37), closures (“Closures” on page 56), and the concept of all values being objects that you can attach properties and functions to (“Extensions” on page 69). Power Swift has access to the entire Objective-C runtime, and is seamlessly bridged to Objective-C’s classes as well as its own standard library. This means that you can use Swift right away to write full iOS and OS X apps—you don’t need to wait for anyone to port any features from Objective-C to Swift. And if you’ve never used 28 | Chapter 2: The Basics of Swift
- 49. Objective-C, then you don’t need to worry about Objective-C! You can do every‐ thing you need to develop for Apple platforms using Swift. So, what does Swift look like? Here’s an example: func sumNumbers(numbers: Int...) -> Int { var total = 0 for number in numbers { total += number } return total } let sum = sumNumbers(2,3,4,5) print(sum) This code snippet does the following things: First, a function called sumNumbers is defined. This function takes one or more Int values, which are integers (whole numbers), and returns a single Int. The Int... denotes that the function takes a variable number of Int values; you can access these values through the numbers variable, which is an array. Inside the function, the variable total is declared. Note that the type isn’t given—the compiler knows that it stores an Int, because it’s being set to the inte‐ ger value of 0. Next, a for-in loop starts up, which loops over every number that was sent to the method. Notice again that the type of the number variable isn’t defined—the com‐ piler infers that, given that numbers is an array of Int values, number should itself be an Int. The value of number is added to total. When the loop is complete, total is returned. The function sumNumbers is called with a collection of integers, and the result is stored in the new variable sum. This variable is constant: by defining it with the let keyword, we tell the compiler that its value never changes. Attempting to change the value of a constant is an error. Finally, we display the value using the print function, which prints values out to the console. There are a few interesting things to note here: The Swift Programming Language | 29
- 50. Another Random Document on Scribd Without Any Related Topics
- 51. Gärtner’s work on hybridisation had been preceded by other enquiries into the same subject, those namely of Knight mentioned above at the beginning of the century, and Herbert’s more ample investigations published in his work on Amaryllideae in 1837. Gärtner did not neglect to compare his observations at all points with the results of his predecessors, especially those of Koelreuter, and he deduced from the astonishing mass of material a number of general propositions respecting the conditions under which the production of hybrids is possible, the results of crossing, and the causes of failure. A special interest attaches to his mixed and compound hybrids, to his experiments on the various degrees of influence which foreign pollen exercises on the behaviour of the female organ, and the connection of this point with the formation of varieties. It is impossible to give a more distinct account of Gärtner’s results without entering into discussions which would exceed the limits of a historical survey. It is the less necessary to do so, since Nägeli undertook in 1865 to give a summary view of all the important results to be found in the wealth of material supplied by Koelreuter, Herbert and Gärtner[112]. Gärtner’s experiments in hybridisation were conducted at Calw in Würtemberg, the place where Koelreuter had made his in 1762 and 1763. And thus it was in two small cities of Würtemberg that the foundations of the sexual theory were laid and the theory itself perfected, as far as it could be by experiment only, by three of the most eminent among observers. Camerarius in Tübingen, Koelreuter and K. F. Gärtner in Calw contributed so largely to the empirical establishment of the theory, that all that was done by others would seem of small importance, if artificial pollination only were in question. But Koelreuter was imperfectly acquainted with the methods by which pollination is usually effected in nature; Sprengel was the first who saw into all their more important relations, and the fact must not be concealed, that Gärtner in regarding Konrad Sprengel’s observations as unworthy of serious consideration, neglected the most fruitful source of new and magnificent results. His careful study of the secreting of nectar and of the sensitiveness of the organs of fertilisation, and his many
- 52. observations on other biological relations in flowers, would have found their natural termination, if he had connected them at all points with Sprengel’s general conclusions respecting the relation of the structure of the flower to the insect world. This Gärtner entirely failed to do, and hence in this case also it was reserved for Darwin’s wonderful talent for combination to sum up the product of the investigations of a hundred years, and to blend Koelreuter’s, Knight’s, Herbert’s, and Gärtner’s results with Sprengel’s theory of flowers into a living whole in such a manner, that now all the physiological arrangements in the flower have become intelligible both in their relations to fertilisation, and in their dependence on the natural conditions under which pollination takes place without the aid of man. Here, as in morphology and systematic botany, Darwin found the premisses given and drew the conclusion from them; here too the certainty of his theory rests on the results of the best observers, on investigations which find in that theory their necessary logical and historical consummation. 7. Microscopic investigation into the processes of fertilisation in the phanerogams; pollen-tube and egg-cells [113]. 1830-1850. Those who were convinced of the sexuality of plants had endeavoured as early as the previous century to form some idea with the help of the microscope of the way in which the pollen effects the formation of the embryo in the ovule. We may pass over Morland’s and Geoffroy’s very rude attempts in this direction: Needham (1750), Jussieu, Linnaeus, Gleichen, and Hedwig imagined that the pollen-grain bursts upon the stigma, and that the granules it contains make their way downwards through the style to the ovules, and are there either hatched into embryos or assist in their production. This way of conceiving the matter was closely connected with the theory of evolution which then prevailed, and seemed to find some countenance in the seed-corpuscles of animals; it was also supported by the observation that pollen-grains placed under the microscope in water often burst and discharge their contents in the
- 53. form of a granular mucilage. It has been already mentioned that Koelreuter rejected this view; he declared the bursting of the pollen- grains to be contrary to nature, and considered the oil which exudes from the grains to be the fertilising substance. This view was adopted by Joseph Gärtner and Sprengel, but it fell into disesteem, while that of Needham and Gleichen commanded some assent some years longer. The next question was, how the granular contents of the pollen-grain reach the ovules. Accident supplied a starting-point for further consideration. Amici, who was examining the hairs on the stigma of Portulaca for another purpose, saw on that occasion (1823) the pollen-tube emerge from the pollen-grain, and the granular contents of the latter, commonly known as the fovilla, execute streaming movements like the well-known movement in Chara. The desire to verify this remarkable fact, and to discover how the fertilising substance is absorbed by the stigma, led Brongniart in 1826 to examine a great number of pollinated stigmas. He succeeded in establishing the fact that the formation of pollen-tubes is a very frequent occurrence. The want of perseverance in following out his observation and a prepossession in favour of Needham’s old theory prevented him from discovering the course of the pollen- tubes all the way to the ovules; he supposed, indeed, that after penetrating into the stigma they open and discharge their granular contents, and he maintained distinctly that these are analogous to the spermatozoids in animals, and are the active part of the pollen. But now Amici addressed himself more earnestly to the question, and in 1830 he not only followed the pollen-tubes into the ovary, but also observed that one finds its way into the micropyle of each ovule. Thus the question was suddenly brought near to its solution, when observers began to wander from the right path in different directions. Robert Brown showed in 1831 and 1833 that the grains in the pollen-masses of Orchids and Asclepiads put forth pollen-tubes as in other plants, and that fine tubes are found in the ovary of Orchids in which pollination has taken place; but he was in doubt about the connection of these tubes with the pollen-grains, and
- 54. rather inclined to think that they were formed in the ovary, though possibly in consequence of the pollination of the stigma. Schleiden went wrong in a very different way, and by so doing made the question as prominent in botanical research, as was that of the origin of cells at this time. He published in 1837 some excellent investigations into the origin and development of the ovule before fertilisation, certainly the best and most thorough of the day. He at the same time showed that Brongniart’s and Brown’s doubts were unfounded, and confirmed the statement of Amici, that the pollen- tubes make their way from the stigma to the ovule, which they enter through the micropyle. But he made them push forward a little too far, for he asserted positively that ‘the pollen-tube pushes the membrane of the embryo-sac before it, making an indentation, and its extremity then appears to lie in the embryo-sac. The extremity of the tube now swells out into a round or oval shape, and cell-tissue forms from its contents; the lateral organs, one or two cotyledons, are then produced, the original apical point remaining more or less free and forming the plumule. The portion of the tube underneath the embryo and the fold of the embryo-sac which envelopes it are divided off sooner or later and disappear, so that the embryo now really lies in the embryo-sac.’ This view, which appears to rest on direct observation and is illustrated by figures which answer to the description, corresponds with the old theory of evolution and has a striking approximation to the ideas of Morland and Geoffroy; and if it were correct, it would like these imply the necessity of pollination to the formation of seeds that should contain embryos, but at the same time it would do away with that which is the essential point in the sexuality of plants, for the ovule would merely be the spot adapted to the hatching of the embryo formed from the pollen. Schleiden’s idea was at once adopted by Wydler, Gelesnow and various other botanists, and especially by Schacht, but the most eminent microscopists withheld their assent. Amici was the first who openly opposed the new doctrine; before the Italian congress of savants at Padua in 1842 he endeavoured to prove that the embryo is not formed at the end of the pollen-tube, but from a portion of the ovule which was already in existence before fertilisation, and that this part
- 55. is fertilised by the fluid contained in the pollen-tube. But the choice of a gourd, a plant eminently unsuitable for his purpose, prevented his discovering the exact details of the process, and Schleiden did not hesitate to denounce his assertions in 1845 in the plainest terms. But in the next year (1846) Amici produced decisive proof for the views which he had maintained; he showed from the Orchidaceae, which were peculiarly well adapted for such investigations, not only that Robert Brown’s doubts above mentioned were without foundation, but, which is the main point, that a body, the egg-cell, is present in the embryo-sac of the ovule before the arrival of the pollen-tube, and that this body is excited by the presence of the pollen-tube to further development, the formation of the embryo. He gave a connected account on this occasion for the first time of the whole course of these processes from the pollination of the stigma to the perfecting of the embryo. The correctness of the account given by Amici was confirmed in the following year by von Mohl and Hofmeister, the latter of whom described in detail the points which were decisive of the question from a variety of plants, and illustrated them by very beautiful figures in a more copious work, ‘Die Enstehung des Embryo der Phanerogamen,’ Leipzig, 1849. Tulasne also came forward in opposition to Schleiden’s theory, being thoroughly convinced that there was no actual contact of the pollen-tube with the egg-cell, denying indeed the existence of the egg-cell before fertilisation. Thus a vehement controversy arose on the subject; a prize offered by the Institute of the Netherlands at Amsterdam was awarded to an essay of Schacht’s in 1850, which defended Schleiden’s theory, and illustrated it by a great number of drawings giving incorrect and indeed inconceivable representations of the decisive points. Von Mohl says very admirably on this occasion (‘Botanische Zeitung,’ 1863, Beilage, p. 7): ‘Now that we know that Schleiden’s doctrine was an illusion, it is instructive, but at the same time sad, to see how ready men were to accept the false for the true; some renouncing all observation of their own dressed up the phantom in theoretical principles; others with the microscope in hand, but led
- 56. astray by their preconceptions, believed that they saw what they could not have seen, and endeavoured to exhibit the correctness of Schleiden’s notions as raised above all doubt by the aid of hundreds of figures, which had every thing but truth to recommend them; and how an academy by rewarding such a work gave fresh confirmation to an experience which has been repeatedly made good especially in our own subject during many years past, namely that prize-essays are little adapted to contribute to the solution of a doubtful question in science.’ In this case the prize-essay had been refuted before it appeared by von Mohl, Hofmeister and Tulasne. Schacht adhered all the more firmly to Schleiden’s theory; after further controversy, in which other writers of less authority took part, Radlkofer published in 1856 a complete review of the question, which fully confirmed Hofmeister’s observations, and gave incidentally an account of Schleiden’s views in the altered form which they had by that time assumed; this account showed in fact that Schleiden had completely retracted his former opinions, and in this retractation Schacht was soon after compelled to follow him, having become acquainted with facts observed in the ovule of Gladiolus, which were obviously irreconcilable with Schleiden’s theory. Hofmeister had from the first directed special attention to the questions, whether any bodies are found in the pollen-tube which answer in any way to spermatozoids, and whether any opening can be perceived at the end of the tube. He found indeed forms in Coniferae in 1851, which reminded him of the male organs of fertilisation in the higher Cryptogams; but the pollen-tube was closed both in them and in the rest of the Phanerogams, in which moreover its outer coat attains to a considerable thickness. There remained therefore only the hypothesis, that a fluid substance passes through the walls of the pollen-tube and of the embryo-sac and effects the fertilisation of the egg-cell; thus it was not the theory of preformation of the last century, to which Brongniart still adhered, but the view represented by Koelreuter, which ultimately proved to be nearer the truth, though it may be said that all that remained of that view was, that the fertilising substance in the Phanerogams is a
- 57. fluid. The granular contents of the pollen-grains, which were supposed to be spermatozoids, have since been partly found to be only innocent starch-grains and drops of oil. 8. Discovery of Sexuality in the Cryptogams. 1837-1860. By the year 1845 no one capable of forming a judgment on the question any longer doubted the existence of different sexes in Phanerogams. But it was not so with the Cryptogams, though a number of facts were acknowledged at this time which seemed to point to the conclusion, that a moment arrives sooner or later in the course of their development also, when a sexual act is accomplished. But the question had not as yet been systematically studied; no experimental investigations had been made, or observations of such a kind as to demonstrate the necessity of sexual union. The great majority of botanists in the second half of the 18th century had no longer any doubt that the stamens were organs of reproduction, and they were anxious to prove the existence of similar organs in the Cryptogams; they rested in this matter on external resemblances and analogies, which they interpreted in a more or less arbitrary manner. The obvious external resemblance between the antheridia and archegonia in Mosses and the sexual organs in the Phanerogams led Schmidel and Hedwig to consider them to be stamens and ovaries, and the conjecture was correct, though the true nature of the moss-fruit had to be learnt in another way. Micheli, Linnaeus and Dillen, trusting still more to external appearance and with slight knowledge of these plants, had before this taken the fruit for a male flower, and in the case of the rest of the Cryptogams the best botanists were only feeling their way in the dark with no certain experience to guide them. It is not necessary to give a particular account of the views which originated in this way; one or two may be mentioned by way of example. Koelreuter regarded the volva of Mushrooms, Gleditsch and Hedwig certain tube-like cells in their lamellae, as the male organs of fertilisation.
- 58. Gleichen took the stomata, Koelreuter the indusium, Hedwig even the glandular hairs of Ferns for anthers. It was not yet suspected that the course of development and the whole morphology of the Cryptogams could not be so compared with that of the Phanerogams; correct and incorrect assumptions with regard to the sexual organs of the Cryptogams were alike devoid of scientific value, being mere guesses and vague conjectures. Nor was the state of things much better even in the first years of the 19th century; and if by that time a number of occasional observations had been made which could afterwards be turned to scientific account, these were as yet only isolated facts without scientific connection, and every one was at liberty to concede or to refuse sexual organs to the Cryptogams generally at his own discretion. Meanwhile observations gradually accumulated, and towards 1845 it began to be possible by critical examination of them to arrive at something like a clearer understanding of this part of botany. The majority of botanists readily accepted Schmidel’s and Hedwig’s opinion with respect to the Mosses; Vaucher had as early as 1803 maintained that the long- known conjugation of Spirogyra was a sexual act; Ehrenberg observed in 1820 the conjugation of a Mould, Syzygites; Bischoff and Mirbel explained the organisation of the antheridia of the Liverworts in 1845, while Nees von Esenbeck saw the spermatozoids of Sphagnum in 1822 and Bischoff those of Chara in 1828, though they were at first taken for Infusoria, an opinion maintained by Unger as late as 1834. But it was Unger[114], who in 1837, after careful study of the spermatozoids of the Mosses in 1837, declared them to be the male organs of fertilisation; in 1844 Nägeli discovered corresponding forms on the prothallium of Ferns, which had till then been called a cotyledon, and in 1846 the spermatozoids of Pilularia, the products of the small spores which Schleiden had explained to be the pollen- grains of that plant. These facts were of the highest importance, but little was to be made of them as long as the female organ in the plants in question, the Mosses excepted, was unknown, and meanwhile it was only the resemblance between vegetable and animal spermatozoids which led
- 59. to the conjecture, that the one had the same sexual significance as the other. Light was suddenly thrown upon the subject, when Count Lesczyc- Suminsky discovered in 1848 on the supposed cotyledon (prothallium) of Ferns both the antheridia and the peculiar organs, inside which the embryo or young fern is formed. Though the statements respecting the structure and development of these female organs and of the embryo were inaccurate in some important points, yet the place was now indicated where it might be presumed that the fertilisation by the spermatozoids takes place; and as the history of the germination of the rest of the vascular Cryptogams was to some extent known through the earlier labours of Vaucher and Bischoff, the organs of fructification of these plants might now be sought, where they are really to be found. But an erroneous idea respecting the meaning of the small spores of the Rhizocarps propounded by Schleiden had first to be put out of the way, and this was done by an appeal to the discovery of Nägeli mentioned above and by the investigations of Mettenius. Then in 1849 Hofmeister supplied a connected description of the germination of Pilularia and Salvinia, in which the decisive points as regards the sexual act were clearly set forth, and the connection of the spermatozoids with the fertilisation of the egg-cells in the archegonium was established. He did the same for Selaginella, which is very unlike the Rhizocarps and Ferns, and in which the spermatozoids are developed from smaller spores, and fertilise the egg-cells in archegonia formed in the prothallium of the large spores. By comparing the processes of germination in these plants with those of Ferns and Mosses, he succeeded in throwing entirely new light on the whole of the morphology of these classes of plants, and thus made it possible for the first time to compare them with one another and with the Phanerogams, and to form a right estimate of the sexual act in the Muscineae and Vascular Cryptogams in its relation to the history of the development of these plants. Hofmeister arrived at the following conclusion from his observations in 1849: ‘The prothallium in the vascular Cryptogams is the morphological equivalent of the leaf-
- 60. bearing Moss-plant, while the leafy plant of a Fern, of a Lycopodium and a Rhizocarp answers to the capsule of the Moss. In Mosses as in Ferns there is an interruption of the vegetative development by sexual procreation, an alternation of generations; this takes place in the Vascular Cryptogams very soon after germination, in the Mosses much later.’ The vast importance of this discovery to systematic botany has been already noticed. The conception of these relations developed by Hofmeister was not less important to the doctrine of the sexuality of plants; it swept away at one stroke all the old false analogies between Phanerogams and Cryptogams and brought to light the real agreement; Hofmeister had detected in the archegonium of the Cryptogams the body which is developed there, as in the ovule of the Phanerogams, into an embryo after fertilisation, namely the germinal vesicle or egg-cell. Here was the point of departure for all further systematic comparison in the sexual propagation of Cryptogams and Phanerogams. All beside was of secondary importance, even the fact, that the fertilisation of the egg-cell in the Cryptogams is not effected by a pollen-tube, but by spermatozoids. It was now easy to show the corresponding relations of generation in the other cases which Hofmeister had not yet observed. Hofmeister’s statements and conclusions respecting Selaginella and Isoetes were confirmed and some additions made to them by Mettenius in 1850, and in 1851 appeared Hofmeister’s exhaustive work ‘Vergleichende Untersuchungen,’ in which the mode of production of the embryo in Coniferae was represented as an intermediate form between those of Phanerogams and Cryptogams. Further contributions were made to the knowledge of the subject; Henfrey confirmed Hofmeister’s results in the case of Ferns; Hofmeister himself and Milde observed in 1852 the history of fertilisation in Equisetaceae, and the former supplied at the same time a more complete account of the development of Isoetes; in 1855 he described the decisive points in Botrychium and Mettenius in 1856 those in Ophioglossum.
- 61. The processes of development before and after fertilisation were now cleared up by all these discoveries, but the direct observation of the act of fertilisation was still wanting. Hofmeister (‘Flora,’ 1857, p. 122) describes the state of affairs in the following terms: ‘While numerous investigations had thrown a clear light on the character of the male and female organs, and on the way in which the embryo is formed by repeated division of the egg-cell present before fertilisation, we continued quite in the dark respecting the particular nature of the fertilisation. Observation and experiment had established the fact, that the influence of the spermatozoids on the archegonia was required to produce an embryo in the latter. Female moss-plants[115] separated from the male, macrospores in the Vascular Cryptogams separated from the microspores, had in all cases proved unproductive; but it was not even certainly known to what point in the female organ the spermatozoids force their way. It is true that Lesczyc and after him Mercklin had seen the entry of moving spermatozoids into the mouth of archegonia in Ferns; but Lesczyc’s account of the part which he supposed them to play there afterwards, was proved to be an illusion. I had myself observed motionless spermatozoids halfway down the neck of archegonia of an Equisetum; but nothing was to be learnt of the manner in which the spermatozoid affects the egg-cell. Then it happened that in the spring of 1851, being engaged in observing the development of the organs of vegetation of Ferns, I repeatedly saw spermatozoids moving about in the basilar cells which enclose the egg-cell in the archegonia of Ferns, and the majority of them even playing about the egg-cell. Their movements were put an end to during the observation by the commencement of changes, which the contents of young vegetable cells which have been cut open usually experience under the prolonged influence of water.’ Later observations leave no doubt now that in the Muscineae and Ferns single spermatozoids force their way into the naked egg-cell of the archegonium. The question was first set at rest in the Algae, where the process of fertilisation could be seen directly and without exposing the
- 62. objects to destructive influences. That sexual propagation occurs in the Algae also had seemed probable, since Decaisne and Thuret in 1845 discovered organs in species of Fucus, and Nägeli in 1846 in Florideae, which scarcely admitted of any other explanation. Alexander Braun also had called attention to the formation of two kinds of spores in a large number of fresh-water Algae. But as yet there was only conjecture. Then Thuret proved by experiment in 1854, that in the genus Fucus the large egg-cells must be fertilised by very small swarming spermatozoids, in order to set up germination; both organs can be collected separately and in numbers in this genus, and be brought together at pleasure; Thuret even succeeded in obtaining hybrids. Pringsheim first observed in 1855 the formation of spermatozoids in the little horns of Vaucheria and established the fact that spores capable of germination are not formed unless the spermatozoids approach the egg-cell. To Thuret’s statements he added the very important one, that the remains of spermatozoids may be recognised on the surface of the contents of the fertilised egg-cell of Fucus, which is already surrounded by a membrane. About the same time Cohn published his observations on Sphaeroplea annulina, which confirmed the fact of the approach of the spermatozoids to the egg-cells, which consequently, as in Fucus and Vaucheria, form a cell-wall and are rendered capable of further development. Still the decisive observation had not yet been made; no one had yet seen how the two fertilising elements behaved at the moment of fertilisation. Pringsheim had the good fortune to make this observation in one of the commonest of fresh water Algae, Oedogonium. There he saw the moving spermatozoid first come into contact with the protoplasmatic substance of the egg-cell, and then force its way into it, blend with it and dissolve. And thus the first observation was made, which proved decisively that a real intermixture takes place of the male and female elements of fertilisation; this important fact was confirmed by De Bary in the same year.
- 63. Now that it was once established, that fertilisation in Cryptogams consists in the blending together of two naked bodies of protoplasm, the spermatozoid and the egg-cell, it was reasonable to conclude that conjugation in Spirogyra and generally in Conjugatae, was an act of fertilisation, only in this case the two fertilisation-elements are not of different size and shape, but similar in appearance. To this conclusion De Bary arrived in 1858 in his monograph of the Conjugatae. This extension of the idea of fertilisation to cases in which the uniting cells are to outward appearance alike, was of special value to the theory of sexuality, as was seen in the sequel, when other forms of fertilisation were observed which made it necessary still further to extend the idea of sexuality. In 1858 Pringsheim discovered arrangements for fertilisation in another group of Algae, the Saprolegnieae, which to outward appearance at least departed widely from those hitherto known in the lower plants. Thus between the years 1850 and 1860 a number of fundamental facts were discovered, and were afterwards confirmed and extended by fresh observations in the course of the following years. It does not fall within the limits of this work to notice the many discoveries that were made in this part of botanical science after 1860; we will only remark, that between 1860 and 1870 the processes of fructification were observed by Thuret and Bornet in Florideae, and especially by De Bary and his pupils in Fungi, in some of which very peculiar forms were brought to light. No doubt any longer exists that difference of sex prevails generally in the Thallophytes also, though it is still an open question, whether it may not be wanting in some of the very simplest and smallest kinds. One of the most important results of these investigations is obviously the striking resemblance between many of the processes of fertilisation in Cryptogams and in the lower animals; here is another confirmation of the fact, often brought out in other ways by modern zoological and botanical research, that the points of resemblance in the vegetable and animal kingdoms appear most plainly, if we compare together the simplest forms to be found in
- 64. both; we have in this fact a plain proof also, that both kingdoms have been developed from like common elements, as the theory of descent implies. With respect to the true nature of fertilisation itself, which is evidently a similar process in the main in animals and plants, we can only say at present, that it amounts in all cases to a material blending together of the contents of two cells, neither of which is capable of further development by itself, while the product of the combination is not only capable of such development, but unites in itself the characteristics of the two parent forms and transmits them to its descendants. That fertilisation is not the intimate union of two bodies possessing a definite form, but that the male fertilising substance at least may be a simple fluid, appears to be distinctly shown by the process in Phanerogams; and we may assume, that in Cryptogams also, the sexual act is not affected by the form of the fertilisation-elements, though a certain shape and power of movement is necessary for the conveyance of the fertilising substance to that which is to be fertilised.
- 65. CHAPTER II. History of the Theory of the Nutrition of Plants. 1583-1860. That plants take up certain substances from their environment for the purpose of building up their own structures could not be a matter of doubt even in the earliest times; it was also obvious, that movements of the nutrient material must be connected with this proceeding. But it was not so easy to say, what was the nature of this food of plants, in what manner it finds its way into and is distributed in them, and what are the forces employed; it was even for a long time undecided, whether the food taken up from without suffers any change inside the plant, before it is applied to purposes of growth. Such were the questions which had engaged the attention of Aristotle, and which formed the chief subject of Cesalpino’s physiological meditations. But the questions respecting the nutrition of plants acquired a much more definite shape in the latter half of the 17th century, when the various phenomena of vegetation began to be more closely observed, and some attempt was made to understand their relations to the outer world. Malpighi, the founder of phytotomy, was the first who undertook to explain the share which belongs to the different organs of the plant in the whole work of nutrition; guided by analogy, he perceived that the green leaves are the organs which prepare the food, and that the material so prepared by them passes into all parts of the plant, there to be stored up or employed for purposes of growth. But this gave no insight into the nature of the substances from which plants prepare their food. On this point Mariotte endeavoured to give such information as could be obtained from the chemistry of his day; and he has the merit of having shown, in opposition to the old Aristotelian notion, that plants convert the food-material which they derive from the ground into new chemical combinations, while the earth and the water supply
- 66. the same elements of nutrition to the most different kinds of plants. It could not escape the notice of physiologists even of that time, that the water which plants take up from the ground introduces into them but very small quantities of matter in solution. Van Helmont in the first half of the 17th century had shown this by an experiment, the results of which, however, led him to think that plants were able to produce both the combustible and incombustible parts of their substance from water. Hales at the beginning of the 18th century formed a different opinion, being led by the evolution of the gases in the dry distillation of plants to conclude, that a considerable part of their substance was absorbed in a gaseous form from the atmosphere. The views propounded by Malpighi, Mariotte, and Hales contained the most important elements of a theory of the nutrition of plants; fully understood they would have taught that one part of the food of plants comes from the earth and the water, and another part from the air; that the leaves change the materials thus obtained in such a manner as to produce from them the substance of plants and to apply this to the purposes of growth; but the ideas were not combined in this way, for during some years after their time botanists were chiefly engaged in observations on the movement of the sap in plants, and they arrived even on this point at very obscure and even contradictory results, because they overlooked the function of the leaves which had already been recognised by Malpighi. All insight not only into the chemical processes in the nutrition of plants, but also into the mechanical laws of the movement of the sap, and generally into the whole internal economy of plants, depends on a knowledge of the fact, that it is only the cells which contain chlorophyll, and therefore in the higher plants the leaves chiefly as consisting largely of such cells, which have the power of converting the gaseous food supplied by the atmosphere into the substance of the plant with the aid of the materials taken up from the soil. This fact is of fundamental importance to the whole theory of the nutrition of plants; it is only by a knowledge of it that we can explain the movement of material connected with nutrition and
- 67. growth, the dependence of vegetation on light, and to a great extent also the function of the roots. But this principle could not be discovered till the new chemical system founded by Lavoisier took the place of the old phlogistic chemistry, and it is remarkable that the discoveries, which laid the foundation of modern chemistry in the period between 1760 and 1780, contributed essentially to the establishment at the same time of the modern doctrine of the nutrition of plants. Ingen-Houss, in reliance on Lavoisier’s antiphlogistic views on the composition of air, water, and the mineral acids, succeeded in proving that all parts of plants are continually absorbing oxygen and forming carbon dioxide, but that the green organs at the same time under the influence of light absorb carbon dioxide and exhale oxygen; and as early as 1796 he considered it probable that plants obtain the whole mass of their carbon from the carbon dioxide of the atmosphere. Soon after (1804) de Saussure proved, that plants, while they decompose carbon dioxide, increase in weight by a greater amount than that of the carbon which they retain, and that this is to be explained by the fact that they at the same time fix the elements of water. He likewise showed that the small quantities of saline compounds, which plants take up from the soil, are a necessary part of their food, and that it was at least probable, that the nitrogen of the atmosphere does not contribute to the formation of nitrogenous substances in plants. Senebier had before insisted on the fact, that the decomposition of carbon dioxide under the influence of light only takes place in green organs. Thus the most important points in the nutrition of plants were discovered by Ingen-Houss, Senebier and de Saussure. But, as often happens in the case of discoveries of such magnitude, their ideas were for a long time exposed to great misunderstanding. They were better appreciated in France than in any other country; Dutrochet and De Candolle were able to see the importance of the interchange of gases in the green organs to the general nutrition and respiration; but others, and especially German botanists, were not content with
- 68. these simple chemical processes as the foundation of the whole system of nutrition and consequently of the whole life of the plant; the theory of the vital force, which was elaborated in connection with the nature-philosophy during the first years of the 19th century, and was generally accepted by philosophers and physiologists, chemists and physicists, preferred to supply the plant with a mysterious substance for its food, which had its source in the life itself and which it called humus. The most obvious considerations, which must at once have shown that this humus-theory was absurd, were entirely overlooked; and thus in the face of de Saussure’s results the food of plants was once more referred entirely to the soil and the roots, as it was in the earliest times; one of the consequences of this humus-theory in combination with the vital force was that the ash-constituents of plants were supposed to be merely accidental admixtures or stimulants, or to be directly produced in the plant by the vital force. In the period between 1820 and 1840 the reaction set in from different quarters against the theory of vital force; chemists succeeded in producing by artificial means certain organic compounds, which had hitherto been regarded as products of that force; Dutrochet discovered in endosmose a process, which served to refer various vital phenomena in plants to physico-mechanical principles; de Saussure and others showed that the heat of plants is a product of respiration, and by 1840 the earlier theory of a vital force might be looked upon as antiquated and obsolete. It remained to restore to their rights the observations of Ingen-Houss and de Saussure, which under the influence of that theory and of the notions respecting the humus had been so utterly misconstrued. Liebig set aside the humus-theory in 1840, and referred the carbon of plants entirely to the carbon dioxide of the atmosphere, and their nitrogenous contents to ammonia and its derivatives; he claimed the components of the ash as essential factors in the nutrition, and taking his stand on the general laws of chemistry endeavoured to obtain chiefly by the method of deduction an insight into the chemical processes of assimilation and metabolism. The whole
- 69. theoretical value of the facts discovered by Ingen-Houss, Senebier and de Saussure was first made apparent by the connection which Liebig succeeded in establishing between the phenomena of nutrition. The doctrine of nutrition burst suddenly into new life; firm ground was gained, and the botanist, no longer distracted by the difficulties raised by the vital force but resting on physical and chemical principles, might now resume the task of investigation. Oxygen-respiration denied by Liebig was first of all re-established by von Mohl and others. Liebig’s views on the source of nitrogen in plants and on the importance of the ash-constituents rested chiefly on general considerations and observations and on calculation, and had now to be tested by systematic investigation and especially by experiments on vegetation in individual plants. And here the place of honour must be assigned to Boussingault, who pursued the path of pure induction as contrasted with Liebig’s deductive mode of proceeding, gradually improved the methods for experimenting on vegetation, and soon succeeded in so producing plants in a purely mineral soil free from all humus, that he finally settled the question of the derivation of the carbon from the atmosphere and of the source of the nitrogen also. He showed from the plants thus artificially nourished, and with due consideration of the many sources of error which beset the question, that the uncombined nitrogen of the atmosphere does not contribute to the nutrition of plants, but that a normal increase in the nitrogenous substances in a plant takes place when the roots take up nitrates as well as the necessary constituents of the ash. With the exception of some doubts which still remained respecting the necessity of certain constituents of the ash, such as sodium, chlorine and silicic acid, the source of the materials which take a part in the chemistry of the nutrition of plants was known before 1860; but the knowledge obtained with regard to processes in the interior of the plant, the origination of organic substances in the processes of assimilation, and the further changes which they undergo was still fragmentary and uncertain, and led to no general and conclusive results.
- 70. 1. Cesalpino. Aristotle had sought to determine the nature of the materials which plants take up as food, and had laid down the proposition, that the food of all organisms is not simple but composed of various substances. This view was correct, but he united with it the erroneous notion, that the food of plants is elaborated beforehand in the earth, as in a stomach, and is made applicable to purposes of growth, so as to exclude the necessity of any separation of excrements in the plant; this error was refuted by Jung, as we shall see, but nevertheless it continued to live as late as into the 18th century, and ultimately quite spoilt Du Hamel’s theory of nutrition. Cesalpino, whom we have learnt to regard as a faithful and gifted disciple of Aristotle, directed his speculations to the mechanical rather than to the chemical side of the question, and chiefly tried to explain the movement of the nutrient sap in plants. He had a larger stock of material drawn from experience at his disposition than his master, and it is instructive therefore to make a nearer acquaintance with his views, because they show how far the old philosophy was in a condition to turn better empirical knowledge than Aristotle possessed to a satisfactory use; they will also show that Cesalpino’s first essays led him to views which can no longer be said to be strictly Aristotelian. In the second chapter of the first book of the work from which we have already quoted, ‘De plantis libri XVI,’ 1583, he raises the question, in what way the food of plants is taken in and their nutrition accomplished. In animals we see the food conveyed from the veins to the heart, which is the laboratory of the warmth of the body, and after it has been finally perfected there, spread abroad through the arteries into all parts of the body; and this is effected by the operation of the force (spiritus) which is generated in the heart from the food. In plants on the contrary we see no veins, or other channels, nor do we feel any warmth in them, so that it is difficult to understand how trees grow to so great a size, since they seem to
- 71. have much less natural heat than animals. Cesalpino explains this enigma by saying, that animals require much food for maintaining the activity of the senses and the movements of their organs. The larger quantity of animal food also requires larger receptacles, namely the veins. Plants on the other hand need less food, because this is only used for purposes of nutrition, or to a very small extent for the production of internal heat as well, and therefore they grow more vigorously and bear more fruit than animals. At the same time plants are not without internal heat, though it cannot be perceived by the touch because all objects seem cold to us, which are less warm than our organ of feeling. That plants moreover have veins, though only narrow ones in accordance with the small mass of their food, is shown by those which yield a milky juice, such as Euphorbia and Ficus, which when cut bleed like the flesh of animals; Cesalpino adds ‘and this is very frequent also in the vine,’ which shows that he made no distinction between milky juice and the exuding water of the weeping vine-stock. These narrow veins cannot be seen on account of their fineness; but in every stem and in every root things may be discerned which like nerves in animals can be split longitudinally and are called the nerves of the plant, or also certain thicker things, such as those which branch in most leaves and are there called veins. These should be considered as food-passages and as answering to the veins in animals; but plants have no main vein like the vena cava in animals, but many fine veins pass from the root to the heart of the plant (cor, root-neck, see above, Book I. chap. 2), and ascend from it into the stem; for it was not necessary that the food should be collected in a common receptacle in plants, as it is in the heart in animals, where this is necessary for the production of the spiritus, but it was sufficient that the fluid in plants should be changed by contact with the medulla cordis (in the root-neck), as it is changed in animals in the marrow of the brain or in the liver; and in these organs the veins are very narrow, as they are in plants. Since plants have no sense-perception, they cannot seek their food like animals, but they draw up the moisture from the ground into themselves in a way of their own; but it is not easy to see how
- 72. this takes place. Cesalpino, in trying to explain this, gives us a glimpse into the physics of the day, and we observe also to our surprise an attempt made to explain phenomena in living creatures by physical laws, a step beyond the limits of Aristotelian modes of thought and in the right direction. It is not the ratio similitudinis, which draws iron to the magnet, that can cause the attraction of the juice by the roots, for then the smaller would be drawn to the larger; and if the attraction of the fluid of the earth by the roots were the same thing as the attraction of the iron by the magnet, the moisture of the earth would draw out the juice from the plant, which is just what does not happen. Nor can it be the ratio vacui; for since not moisture only but air also is contained in the earth, the plant would be filled not with juice but with air. But Cesalpino hits upon a third kind of cause by which juices may be drawn into the plant. Do not many dry things, he says, in accordance with their nature attract moisture, as linen, sponge and powder, while others repel it, as the feathers of many birds and the herb Adiantum, which are not wetted even when dipped in water; but the former absorb much water, because they have more in common with it than with air; of this kind Cesalpino thinks those parts of plants must be, which the nourishing soul employs to take in food. Therefore these organs are not traversed by a continuous canal such as the veins in animals, but formed like the nerves of a fibrous substance; and thus the power of suction (bibula natura) conveys the moisture continually to the place, where the principle of internal heat is placed, just as may be seen in the flame of a lantern, to which the wick continually conducts the oil. The absorption of the moisture is also increased by the outer warmth, for which reason plants grow more vigorously in spring and summer. That Cesalpino had no suspicion of the use of the leaves in the nutrition of plants appears incontestably from his repeating the Aristotelian idea, that the leaves are only for the protection of young shoots and fruits from air and sun-light; this idea is no result of speculation, but came simply from observing a vineyard in a hot country.
- 73. 2. First inductive experiments and opening of new points of view in the History of the Theory of the Nutrition of Plants. All that Aristotle and his school, Cesalpino not excepted, are able to tell us about the phenomena of vegetable life, was the result of the most every-day observations, none of which were critically and exactly tested to ascertain their actual correctness, while the larger part of their physiological axioms were not derived from observations on plants at all, but from philosophical principles, and especially from analogies taken from the animal world. The first step towards a scientific treatment of the doctrine of nutrition was an enlargement and critical examination of the materials to be gained from experience; nor were any difficult observations or experiments needed to discover contradictions between the truths of nature and the old philosophy; all that was necessary was to look into things more closely and to judge of them with less prejudice. In this way Jung was led to oppose one important point of the Aristotelian account of nutrition. In the second fragment of his work ‘De plantis doxoscopiae physicae minores’ is to be found a remark, which is evidently directed against the notion that plants receive their food already elaborated from the earth, and therefore give off no excrements[116]. Plants, says Jung in accord with Aristotle, appear not to need a thinking soul (anima intelligente), which would be able to distinguish wholesome from unwholesome food, and Aristotle therefore provided them with food which had already been perfectly prepared in the earth. But Jung takes another view founded on actual observation. It is very possible, he says, that the openings in the roots which take in liquid matter are so organised, that they do not allow every kind of juice to enter, and who can say that plants have the peculiarity of only absorbing what is useful to them, for like all other living creatures they have their excreta, which are exhaled through the leaves, flowers, and fruits. But among these he reckons the resins and other exuding liquids, and says that it is
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