Part 1
7 vw — y , BOTANY FOR AGRICULTURAL STUDENTS - BY JOHN N. MARTIN Professor of Botany at the Iowa State College of Agriculture and Mechanic Aris ~ FIRST EDITION NEW YORK JOHN WILEY & SONS, Inc. Lonpon: CHAPMAN & HALL, Lmirep 1919 Copyricut, 1919, BY JOHN N. MARTIN e . e ¢ .: ‘ 2°. 8 . . e Ld ° ry e ied Ld . ae . e on ee *,° a". * ° e e ,: @ . eo (U8 eo. ® e “. ; ee e e s¢ ry Stanbope [press F H.GILSON COMPANY BOSTON, U.S.A. al oe \ L> Ne 1, \ ? hea + -OGY PREFACE Although students vary widely in their reasons for studying Botany, the fundamental facts or principles of the subject are not thereby altered. One has considerable freedom, however, in the presentation of the subject to adapt the subject matter to special aims of different classes of students, and especially is this true in courses for agricultural students, since much of the work in Agricilture is based upon the principles of Botany. In the choice of material to illustrate principles and in the presen- tation of the applications_of principles, there is special oppor- tunity to relate courses in Botany to courses in Agriculture. In any elementary course in Botany, regardless of the kind of education the student desires to obtain, the primary aim should be to give the student a notion of the fundamental principles of Botany. This aim should be the guiding one in both recitation and laboratory, determining the trend of discussions in recita- tion, and the nature of the material and procedure in the lab- oratory. The primary aim should be accompanied by a secondary aim to relate the subject to the student’s major line of work. When the relation of the subject to major lines of work is obvious, the student is more likely to appreciate the subject and is thereby put in a favorable mood to study the subject. Even for students who take Botany merely as a part of a general education, it in no way detracts from the course or makes botanical training less efficient to present the practical aspects of the subject. This book is intended for elementary courses in Botany in colleges and universities. In its preparation the aim has been to present the fundamental principles of Botany with emphasis upon the practical application of these principles. The subject matter is presented in two parts, part I being devoted to the study of the structures and functions chiefly of Flowering Plants, and Part IT, to the study of the kinds of plants, relationships, Evolution, Heredity, and Plant Breeding. In the preparation of the book, I had the following objects in view: (1) to present the structures and functions of Flowering or ge eam Ee Iv PREFACE Plants and relate them to such agricultural subjects as Farm Crops, Forestry, and Horticulture, and to the more advanced courses in Botany; (2) to present the kinds of plants with emphasis upon their evolutionary relationships and their economic im- portance; and (3) to present Evolution, Heredity, and Plant Breeding as related to the improvement of plants. The topics are arranged in the book in the order in which I usually present them. The presentation of the reproductive structures and processes of Flowering Plants, followed by that of the vegetative organs, has fitted in at Iowa State College with the time of year at which the agricultural students begin the study of Botany and also with the courses in Agriculture. In other schools where conditions are different, other arrangements of the topics are more suitable. In recogni- tion of this fact, most of the chapters have been written so as to be separately understandable, the aim being to make the book adaptable to any arrangement of topics that the teacher may prefer. In the discussion of a subject the presentation of the general features precedes that of the particular features, and the latter are presented in most cases by the study of type plants chosen on account of their familiarity and economic importance. The book is intended for an entire year’s work in Botany and ' to be accompanied by laboratory work. Where less time is de- voted to the subject, the organization of the chapters so as to be separately understandable permits a selection of topics according to the requirements of the course. The reproductive structures and processes in Flowering Plants (Chapters III and IV) are dwelt upon more than is necessary for students who have had a good course in Botany in a high school. A large percentage of the students in my elementary classes have had no Botany and have difficulty in understanding sexual reproduction in Flowering Plants. In an effort to thor- oughly acquaint the student with this subject, I have dwelt at considerable length upon those phases of the subject that are in my experience difficult for the student to understand. In case students are familiar with this subject, parts of Chapters III and IV can be omitted or read hastily in review. Usually there are some students in the class that are especially interested in certain topics and desire a more complete discussion PREFACE V of the topics than the text affords. In recognition of this fact, I have added, chiefly as footnotes, many references. Most of the references are bulletins on the special topics, and in addition to giving further information on the special topics, these references introduce the student to that vast source of information contained in the bulletins published by the U. 8. Department and the ex- periment stations of the different states. Many of the illustrations have been taken from the publica- “ions of various authors whose names or the names of their pub- lications appear in connection with the illustrations. To these authors I am much indebted. Most of the original illustrations have been made by Mrs. Edith Martin, who has also given me valuable assistance in other ways in the preparation of the book. Also much credit is due Mr. H. 8. Doty and Mr. L. E. Yocum, my assistants, who have given me valuable suggestions. To Dr. L. H. Pammel, who read some of the topics on Fungi and offered valuable suggestions, I am also much indebted. The book no doubt has many faults, but I hope it has some particular value and that the criticisms which teachers offer will make me a more efficient teacher. J. N. MARTIN. Ames, Iowa . Oct. 7, 1918 CONTENTS INTRODUCTION CHAPTER PAGE I. Toe NaTuRE AND SUBDIVISIONS OF BOTANY ....ee-s 1 II. A GENERAL Vrew or PLANTS ....... oe ee wee 5 PART I Piants (CHIEFLY SEED PLANTS), AS TO STRUCTURES AND FUNCTIONS 2TTI. Frowers ..... 2... 2... ee eee ee ew ews 9 General characteristics and structure of flowers. ..... 9 Some particular forms of flowers .........28.6-. 16 Arrangement of flowers or inflorescence ......... 26 IV. Pistms anD STAMENS. .... 1... 2 ee ee we eee 33 Structure and function of pistils and stamens ...... 33 Pollination. . 2... 2 1 ew ee ee ew te tw te wwe 46 V. Seeps AND FRUITS ..... 1... 0 ee ee eae os. 55 Nature and structure of seeds ......... 20 ee. 55 Resting period, vitality, and longevity of seeds . . .... 67 Purity and analysis of seeds ..........6e6e8-8 74 Nature and types of fruits of Flowering Plants ...... 77 Dissemination of seeds and fruits ..........62.-. 82 VI. GERMINATION oF SEEDS; SEEDLINGS ........4... 89 Nature of germination and factors upon which it depends . 89 Germinative processes... 2. 1 1 1 1 ee ee et ew 93 Testing the germinative capacity of seeds ...... - - 98 Seedlings ...........880c888-8 ce ee 102 VII. CeLts anp Tissvurs ........ eee wee eo oe ee 112 Structure and function of cells . ..... eee eo we © » 112 Respiration ........08 2.20 c ee ce ee eee 121 Cell multiplication . ....... rrr ~ .. 123 General view of tissues . .....2.2.. ee - - 126 vill CONTENTS CHAPTER . PAGE VIII. Roors. .......-+ 24-2 ee eae ee ew ew ee es 188 General features of roots .......2 +566 oe © «© © 185 Root structure... ......446+4-+4088+8 ce eee 143 Factors influencing the direction of growth in roots . ... 150 The soil as the home of roots. . . ......2e see. 152 Water, air, and parasitic roots . . . 1... 1 6 ee ew 162 Propagation by roots .......4.-.46ee-. ooo « « 163 IX. Srems. .. 2... 1. we et ee te wt tt tee 166 Characteristic features and types of stems ........ 166 General structure of stems... ..... 2... ee ee 166 Structure of monocotyledonous stems .......... 187 Structure of herbaceous dicotyledonous stems ...... 192 Structure of woody stems ............... 197 X. Bups: GrowTs OF STEMS; PRUNING; PROPAGATION BY SteEMs 204 Buds ...... Le te eee eee 204 Growth of stems ............ 60800808 213 Pruning ...... 1... ee ee ee ew eee ee 221 Propagation by means of stems... ......-.2.6.. 225 XI. LEAVES .... 2... ee ee ee ee ee et tee 233 Characteristic features of leaves... .... 2.2... 233 Primary and secondary leaves .........2.2..6. 234 General structure of leaves. . . . 2... ee ee ee 242 Cellular structure of leaves. . 2... 1. 1 we ee ee 246 The manufacture of food by leaves ........2... 252 Factors influencing photosynthesis ........... 257 Transpiration from plants ........4++.seee0e8-. 260 Respiration . . 2... 1 ee ee ee te tt te tw 269 Special forms of leaves . . . 1... 1 ee se we eee 270 Uses of the photosynthetic food ..... cee ee 273 PART II : PLants as TO KINps, RELATIONSHIPS, EVOLUTION, AND HEREDITY XII. INTRODUCTION .. 2.1. 1 ee eee we et we ee ee 289 XIII. THALLOPHYTES ...... 2... 2 eee ewe we wen 296 Algae (Thallophytes with a food-making pigment) ... . 296 General characteristics . .. 1... 1 eee ee ee 296 Blue-green Algae (Cyanophyceae). . . .. 1... eee 297 Green Algae (Chlorophyceae) ........424ee-2 301 Brown Algae (Phaeophycese) ........2.- , 318 Red Algae (Rhodophyceae) ..........4+-- 324 Some Alga-like Thallophytes not definitely classified . . 329 CONTENTS 1X CHAPTER PAGE XIV. THALLOPHYTES (continued)... 1... 6 eo es ee eevee 336 Myxomycetes and Bacteria (Thallophytes lacking food- making pigments). . .. 1... 1 eee ee eee 336 Myxomycetes (Slime Molds). ............ 336 Bacteria... . 1. 1 1 ew ee te we we te wt we wes 341 XV. THALLopHYTES (concluded). . 2... 1.0 1 1 ww ee ew 351 Fungi (Thallophytes lacking food-making pigments). . . . 351 Phycomycetes (Alga-like Fungi) ........... 353 Ascomycetes (Sac Fungi) and Lichens ......... 363 Basidiomycetes... .... 2... 1 ee ee ee es 382 Fungi Imperfecti (Imperfect Fungi) ......... 404 XVI. Bryropuytes (Moss PLANTS) ..........2e04.8-. 405 Liverworts and Mosses ........4+-++2 sees 405 Liverworts... 1... 1 we ee ew te ht we 406 Mosses. . . 2. 2 ee ee ee ee te ee tee 417 XVII. PreripopHyTes (FERN PLANTS) .........2ee8-s 425 Filicales 2. 2 2 1 Ww we ee te te et tt ee 426 Equisetales (Horsetails) . . .. 2... ee we ee ee 435 Lycopodiales (Club Mosses) . ........+-+4-+e06-8 438 XVIII. Spermatophytes (Seed Plants) ...... 1. 6 we ee eee 445 Gymnosperms (Seeds not enclosed) .........+.-. 445 Cycads (Cycadales) . . 2... 1 2 we we ee te ws 446 Pines (Pinaceae) . . . 2. 1. 6 2 ee ee ew wt we 451 XIX. Spermatophytes (continued) ...... 2-2 2 ee eee 459 Angiosperms (seeds enclosed)... ......+.4+-+8-. 459 . CLASSIFICATION OF ANGIOSPERMS AND SOME OF THEIR FamtI- LIES OF Most Economic IMpoRTANCE. ....... 471 Dicotyledons (Apetalae) .. ...... 5. + we ew ee ee 473 Dicotyledons (Polypetalae) .........22880e0- 481 Dicotyledons (Sympetalae). . ...... 2.5.20 ee ee 489 Monocotyledons .........0+40+5+e0e 2 eee 495 XXI. Ecological classification of plants .........6.++.-. 500 Nature of Ecology ........ 5602 0 ee eee 500 Ecological factors... 2... eee ee we we tee 501 Ecological societies . . 2... 1 ee ee te tw te we ees 504 Plant succession. . . . 1... 6 ee ee ee te ee ees 510 XXII. Evoturion ..........0.2020e8088 Cw ee 513 Meaning and Theories of Evolution. .......++.-. 513 Experimental Evolution... ..... 2 ee ee eee 524 XXIII. Heredity... .........2. 20. ce ee ew wees 535 General features of Heredity .. . 2... 1 0 eee eee 535 Experimental study of Heredity ...... 2.2 eee 537 x CONTENTS CHAPTER PAGE XXIV. Puanr BREEDING. ......---+-- ce eee eee 557 Selection. . . 2. 2 e wee a er ee er ee 557 Mass culture. .... a 558 Pedigree culture .. 1... 2-2 eee eee eres 560 Selection of Mutants ........-58 0+ eee eee 561 Hybridization . 2... 1. 1 1 ee ee ee ee es 561 Crossing and vigor of offspring . . .. 6.6 +s se ee 564 BOTANY FOR AGRICULTURAL STUDENTS INTRODUCTION Botany for Agricultural Students CHAPTER I THE NATURE OF BOTANY Botany is a branch of Biology which includes all of the sciences that deal with living things. Zoology, Bacteriology, Human Anatomy and Physiology are some other biological sciences that are familiar and closely related to Botany. The word botany comes from a Greek word, bosko, meaning, “T eat.’ Botany was originally the science of things good to eat, and in its naming the fact was recognized that plants are the source of our food. Of course at the present time Botany studies all kinds of plants which include besides the many useful for food, many useful as medicine, and many that are poisonous. Botany is commonly defined as that science which treats of plants. This definition is not entirely satisfactory because it does not separate Botany from such agricultural subjects as Horticulture, Forestry, and Farm Crops which also treat of plants. Between Botany and those agricultural subjects which study plants, there is no sharp division line. Much of the work in these agricultural subjects is based upon the principles of Botany. Such features as plant structures, plant functions, and relation of functions to sunlight, air, soil, etc., which are studied in Botany, are features of consideration in Horticulture, Forestry, and Farm Crops. Although Botany and these agricultural subjects study many plant features in common, the latter subjects differ from Botany in studying only special groups of plants, and in limiting the study to the practical and economic phases of plants. A plant may be studied in a number of different ways. It may be considered in reference to structure, functions, and in relation to other plants. Botany is divided into a number of subjects which consider different phases of plant life. 1 2 ' ‘THE NATURE 'Q¥ BOTANY Morpuo.oey considers the form and structure of plants. It considers the forms of plant bodies and the organs and tissues which compose them. Morphology studies the structure of roots, stem, leaves, buds, and flowers, and establishes the rela- tionships of organs. Morphology not only considers the more complex plants but also the simpler ones, and traces the develop- ment of plant structures through the different plant groups. The phase of Morphology in which the development of the more complex plants from the simpler ones is studied, is called Plant Evolution. When Morphology is concerned with the micro- scopical study of the finer structures of plants, then it is called Anatomy, and if the study is mainly concerned with the structure of the cell, then it is called Cytology. Anatomy and Cytology are often spoken of as Histology. Another phase of Morphology is Embryology which, as the term suggests, is the study of the embryo, or the study of the plant during its formation in the seed. Puant Puysio.oay studies the functions of plant structures and the relation of these functions to light, temperature, air, soil, etc. It treats of how the plant lives, respires, feeds, grows, and re- produces. In the study of Plant Physiology we learn how plant food is made and transported, and how plants grow. As a basis for the study of Plant Physiology, one must have a knowledge of the Morphology of plants and also a knowledge of Chemistry and Physics. - Priant PatHo.oey treats of plant diseases. In this subject one learns the disease producing plants and how they affect the plant diseased. In the study of Plant Pathology, in order to know how the diseased plant is injured, one must know the nature and function of the tissues attacked. This means that one should know Morphology and Plant Physiology. Furthermore, in order to know how the disease producing form attacks other plants and propagates itself, one needs to know its Morphology and Physi- ology. Piant Ecox.oey considers plants in relation to the conditions under which they live. Some plants can live on a dry hill top, while others can live only in moist, shady places. Some can live in colder regions than others. Some plants, like many of the weeds, can thrive when crowded among other plants, while some like the Corn plant can not. Marshes, bogs, forests, sandbars, etc., all have their characteristic plants. One set of plants often