0IOLOGY LIBRARY G TWENTIETH CENTURY TEXT-BOOKS TEXT-BOOKS IN BOTANY By John M. Coulter, Ph.D. HEAD OF DEPARTMENT OF BOTANY IN THE UNIVERSITY OF CHICAGO Elementary Studies in Botany. Part I, Plants in General; Part II, Plants in Culti- vation. 12mo, Illustrated, Cloth . . $1.30 A Text-Book of Botany. 12mo, Illus- trated, Cloth $1.25 Plant Studies. An Elementary Botany. 12mo, Cloth $1.25 Plant Relations. A First Book of Botany. 12mo, Cloth $1.10 Plant Structures. A Second Book of Bot- any. 12mo, Cloth $1.20 Plants. The two foregoing in one volume. 'For Normal Schools and Colleges. 12mo, Cloth $1.80 In the Twentieth Century Series of Text-Books D. Appleton and Company, New York *87 TWENTIETH CENTURY TEXT-BOOKS ELEMENTARY STUDIES IN BOTANY BY JOHN M. COULTER, A.M., PH.D, HEAD OF THE DEPARTMENT OF BOTANY UNIVERSITY OF CHICAGO D. APPLETON AND COMPANY NEW YORK CHICAGO BIOLOGY R G COPYRIGHT, 1913, BY D. APPLETON AND COMPANY PREFACE IT is seven years since A Text-book of Botany was published, and during this period there has been not only great progress in the knowledge of plants, but also much discussion con- cerning the effective use of plants in a high school education. It is natural that a discussion of this kind should lead to considerable diversity of opinion, and it is evident that no one is in a position as yet to decide the points at issue. Amid all the flux of opinion, however, there is evident a desire to relate plants more closely to the interest and to the need of high school students. This desire expresses itself in an extreme form when courses in " agriculture " are asked to be substituted for courses in " botany." This has brought a distinct temptation to publishers and to authors to " meet the demand " without much consideration as to its signifi- cance. It cannot mean that all that has proved good in the older method is to be abandoned, and an unorganized mass of new material substituted for it. It cannot mean that high school pupils are to become apprentices rather than students. It must mean that the structure and work of plants are to be so studied that this knowledge will enable the student to work with plants intelligently. In other words, it is intended to be the practical application of knowl- edge, rather than practical work without knowledge. The present book, Elementary Studies in Botany, comprises two parts, intended to meet the two needs indicated above. Part I, Plants in general, gives an account of the structure and work of plants simple enough to be understood by high school students of any grade, and brief enough to be com- vi PREFACE pleted in a half year. At the same time, illustrations are taken from economic plants, and practical applications in the handling of plants are suggested. In other words, this part is intended to develop some real knowledge of plants in con- nection with a practical outlook. In telling the story of plants, advantage is taken of the evolutionary point of view merely as a teaching device. This method of presentation has been very efficient in securing a grasp of the most impor- tant facts and in developing a perspective that lays emphasis where emphasis belongs. Part II, Plants in cultivation, gives an account of the prac- tical handling of plants in the field and in the garden, so far as this can be accomplished in a half year of work. It is the application to practice of the knowledge developed in connection with the work outlined in Part I. The great variety of crops and of cultural conditions forbids a series of specific directions in reference to even the principal crops. Even if this were possible, it would result in a series of direc- tions resembling the recipes of a cookbook, some of them applicable in one locality and some in another, which is very far removed from the idea of a text-book. The plan is to develop some experience in handling the conditions that affect plants, so that any plant may be cultivated, in its appropriate conditions, with some knowledge of the things that must be done. In case only a half year is given to Botany, Part I is rec- ommended for use. It is complete in itself and represents the real basis for further progress. It will be possible to use Part II alone for a half year course, but the reasons for the practice involved will not be so evident as when it follows Part I. The two parts taken together represent a full year of work, which should combine the demand for training in science with that of training in the culture of plants. Neither of the parts will serve its purpose unless it is used as a supplement to the teacher, to the laboratory, to the PREFACE vil experimental garden, and to field-work. Furthermore, it it must be insisted that the sequence of each of the parts need not be the sequence used by the teacher. For example, in Part I, work on leaves, stems, roots, and seeds may come first, to be followed by the general story of the plant kingdom. The sequence may well differ according to the availability of material or the conviction of the teacher. In the laboratory work, it is recommended that the indi- vidual work of the pupils be concerned with the gross struct- ures and behavior of plants chiefly, reserving for occasional demonstration such structures as must be seen under the compound microscope. It is not necessary that the actual forms referred to in the book be obtained in every case. The plant kingdom is represented in every neighborhood, and it is far better to become acquainted with some of the local algae, fungi, liverworts, mosses, etc., than to send for material that does not belong to the possible experience of the student. In the study of Seed-plants, and of course in Part II, it is necessary to arrange for the growing of plants under observation, and the plants selected should be those ordinarily used in gardens or fields, especially those that germinate quickly. The illustrations have been cared for by my colleague, Dr. W. J. G. Land, and unless otherwise credited, all illustrations have been prepared for this volume or its predecessors. JOHN M. COULTER. CHAPTER I. CONTENTS PART I PAGE 1 II. g III. FOOD MANUFACTURE . 31 IV. 40 V. BRYOPHYTES . 66 VI. PTERIDOPHYTES . 88 VII. SPERMATOPHYTES. 1. GYMNOSPERMS . 114 VIII. SPERMATOPHYTES. 2. ANGIOSPERMS . 129 IX. THE FLOWER AND INSECT-POLLINATION . 151 X. DISPERSAL AND GERMINATION OF SEEDS . 167 LEAVES ......... . 18? XII. STEMS . 224 XIII. ROOTS . 253 XIV. PLANT ASSOCIATIONS . 272 PART II I. INTRODUCTION . 295 II. WHAT PLANTS NEED . . . . . . . 300 III. WHAT THE SOIL SUPPLIES . 308 IV. SEEDS . 317 V. OTHER METHODS OF PROPAGATION . 326 VI. PLANT-BREEDING . 333 VII. CEREALS AND FORAGE PLANTS .... . 342 VIII. VEGETABLES . 367 IX. FRUITS . 387 X. FLOWERS . 401 XL FIBER PLANTS . 411 XII. FORESTRY ......... . 419 XIII. 432 INDEX . 455 PART I PLANTS IN GENERAL CHAPTER I INTRODUCTION 1. Occurrence in plants. — Plants form the natural cover- ing of the earth's surface. So generally is this true that a land surface without plants seems remarkable. Not only do plants cover the land, but they abound in waters as well, both fresh and salt. One of the most noticeable facts in regard to the occurrence of plants is that they do not form a monotonous covering for the earth's surface, but there are forests in one place, meadows in another, swamp vegetation in another, etc. In this way the general appearance of vegetation is exceedingly varied, and each appearance tells of certain conditions of living. Such plants as appear to the casual observer in a landscape or in a cul- tivated field are by no means the only plants. They are simply the most obvious or the most useful plants, but associated with them are hosts of plants simpler in struc- ture and smaller in size, grading down to forms so small that they are visible only through a microscope. Any general view of the plant kingdom must include all plants. 2. Plants as living things. — It is very important to begin the study of plants with the knowledge that they are alive and at work. It must not be thought that animals are alive and plants are not. There is a common impres- sion that to be alive means to have the power of locomotion, but this is far from true ; and in fact some plants have the power of locomotion while some animals do not. Both plants and animals are living forms, and the laws of living that animals obey must be obeyed also by plants. It is for this reason that the term biology (the science that deals with 1 STUDIES IN BOTANY living things) applies to both plants and animals. There is so much confusion in the use of this word that it should be understood at the outset that biology deals with all living things, and that plants and animals are two groups of living things. To begin with the thought that plants are alive and at work is important, because this fact gives meaning to their forms and structures and positions. For example, the form and structure and position of a leaf have no -meaning until it is discovered how these things enable the leaf to do its work. 3. Plants and human needs. — It is evident that the material welfare of the human race is largely based upon the work of plants. Not only do they furnish the fundamental food supply for all living things, but in innumerable minor ways they contribute to the necessities of human life. This important relation to human needs has resulted in grouping plants into those that are useful and those that are not, the inference often being that the latter are not so im- portant for study as the former. If useful plants are to be made to yield the largest returns under cultivation, it is absolutely necessary to understand their structure and work. It is also true that plants can explain one another, and many " useless" plants can interpret useful ones. As a rule, the simpler plants are not used by man, but they are necessary to explain the more complex ones that he does use. It is further true that the scientific study of plants, whether useful plants or not, suggests methods of making useful plants more useful. For example, the practical work of agriculture can be improved only as the scientific work with plants points out the way. The most effective way to study useful plants, therefore, is to study the structure and work of plants in general. 4. Plant work. — Although many different kinds of work are being carried on by plants, all the work may be put under two heads : nutrition and reproduction. This means INTRODUCTION 3 that every plant cares for two things : (1) the support of its own body (nutrition), and (2) the production of other plants like itself (reproduction). In the cultivation of plants nothing is so important as to know about their nu- trition and reproduction. Knowledge of the nutrition of plants enables one to secure vigorous plant bodies, and knowledge of the reproduction of plants enables one to secure desirable races of plants. Most cultivators of plants follow rules that they do not understand, but to learn such rules without learning plants makes one an apprentice rather than a student. 5. Various aspects of plants. — Plants are studied from numerous points of view, so that botanists are divided into many groups. The oldest subject of study was the classi- fication of plants, which means discovering their relation- ships, assigning them to natural groups, and giving them names by which they may be recognized. In human society, such a study would be the recognition of family relation- ships, the grouping of people by families, and the use of names to distinguish individuals. Just as individuals are distinguished by two names, so two names are given to ^ach kind of plant, and Quercus alba (white oak) is the name of a plant, just as John Smith is the name of an individual. Plants differ from human individuals, however, in that they have no family records, so that botanists are compelled to trust to certain resemblances to indicate the family connec- tions. This means that plant classification must change as the knowledge of resemblances and differences increases, so that the work of classification demands continuous attention. A second subject of study is the structure of plants. At first only such structures were included as could be seen with the naked eye ; but with the invention and improve- ment of the microscope, the minute structures came to be studied also, so that it was possible to know how the body of a plant is made. This led later to a study of how the 4 ELEMENTARY STUDIES IN BOTANY body of a plant develops, from the egg to the adult; and still later to conclusions as to how plants develop from one another, a subject which is called evolution. If the classifi- cation of plants is likened to the recognition of the family connections and the names of people, the study of the structure of plants may be likened to the study of the struc- ture of the human body and the details of its development from the egg to the adult. A third subject of study is the work of plants. It must be remembered that plants are living things that use food, grow, and reproduce, and all this means the work of a liv- ing body. The study of the structure of plants is like the study of the parts of an engine and how they are put together, but the study of the work of plants is like the study of the engine in action. It is evident that a study of the structures of plants finds its meaning in helping one to understand the activities of plants, just as a study of the structure of the human body finds its motive in helping one to understand the human body alive and doing its work. A fourth subject of study is the diseases of plants, which often ravage our crops. The chief causes of these diseases are other plants, so that this study involves a knowledge of the structure of two sets of plants, those that attack and those that are attacked. In addition to this, it involves a knowledge of two kinds of work, the work of the plant when in health and its work when diseased. The study of plant diseases is regarded as a very practical one, but it is evident that it cannot be carried on effectively without a previous knowledge of the structure and work of plants. Among the plants that induce disease in other plants are the bacteria, which are also conspicuous in causing certain diseases among human beings. These minute and peculiar plants require such special treatment for their study that they form a subject by themselves and demand a specially trained group of botanists. INTRODUCTION 5 A fifth subject of study is the life-relations of plants. Plants become related effectively to such things outside of themselves as light, water, soil, and other plants, and how this is accomplished is the subject referred to. Plants may be studied as individuals relating themselves to their surroundings, just as a human individual may be studied as he adjusts himself to the conditions of life in a city; or they may be studied in " vegetation masses," such as forests or prairies, just as groups of people in a city may be studied as they adjust themselves to other groups. One great natural vegetation mass is of such practical importance that it has developed the special subject of forestry. A sixth subject is known as plant-breeding, and it has become of great scientific and practical importance. It means the growing of plants, generation after generation, under observation and control, and trying to discover the laws of inheritance, which we usually call heredity. This is the great scientific importance of plant-breeding. Its practical importance comes from the fact that the scien- tific work has suggested methods of improving our old plants, producing new ones, and guarding our crops against disease and drought. From the standpoint of our material in- terests nothing can be more important, for it lies at the basis of the world's food supply. The six aspects of plants described above do not exhaust the list, but they are conspicuous illustrations of the fact that botany is not a single study, but includes many kinds of study. 6. Simple and complex plants. — Plants differ greatly not only in size, from microscopic forms to huge trees, but also in complexity of structure. Some plants are so simple that all regions of the body are alike, while others are so complex that the body consists of many kinds of structures. Although the structure of simple and complex plants is 2 6 ELEMENTARY STUDIES IN BOTANY very different, they do the same kinds of work. The work does not become more complex, but the structures developed to do it become more complex. It is believed that the simple plants were the first mem- bers of the plant kingdom, and that plants gradually be- came more and more complex until the structure of our highest plants was reached. To understand the structure of the higher plants, it is necessary, therefore, to approach it as plants approached it, by beginning with simple forms and noting the appearance of one change after another until the greatest complexity is reached. It happens that the plants we use most are most complex, and therefore the tendency has been to study them first and often to study them only; but we are assuming in this book that a study of plants is intended to develop some real knowl- edge of plants. Therefore, in the following pages we will begin with the simplest plants, and discover how the plant kingdom gradu- ally became what it is. In this way we shall really know something of the structure and work of the plants we use most. 7. The four great groups. — It is customary to divide the plant kingdom into four great groups. These groups proceed from the simplest to the most complex plants, so that it will be helpful to obtain a glimpse of them in advance, as this will explain the order in which the plants are presented. (1) Thallophytes. — These are the simplest plants, and therefore the lowest group. The name means "thallus- plants," and a thallus is a simple kind of plant body which will be understood when it is met. The conspicuous mem- bers of this group are called Algae and Fungi, the former being the " seaweeds/' although many of them live in fresh water, and the latter including such forms as mush- rooms among their higher members. INTRODUCTION 7 (2) Bryophytes. — These are the first plants that in- habited the land surface. The name means " moss-plants," for the mosses are the most numerous representatives of the group. (3) Pteridophytes. — These are the first plants that de- veloped a woody system. The name means " fern-plants," for the ferns are the most numerous representatives of the group. (4) Spermatophytes. — This highest group developed seeds, and the name means " seed-plants." Most of them also developed flowers, and they are sometimes called " flowering plants." It is the seed-plants that man uses most, but to understand and explain them, one must know the other groups. ' CHAPTER II THALLOPHYTES. — 1. THE PRIMITIVE PLANTS 8. Definition. — Algae are called the primitive plants because they are thought to have preceded the other groups historically. This does not mean that they were neces- sarily the first plants, for plants that have disappeared, or that we have failed to recognize, may have preceded the Algae. But in our present flora, as an assemblage of plants is called, the Algae appear to be the forms that have given rise to the other groups. They are comparatively very simple, but not necessarily very small, for certain seaweeds become as bulky as do the higher plants. The Algse are of very little practical importance, hence their study is not due to the fact that men use them. But they are of very great scientific importance, because they illustrate the beginnings of the plant kingdom, and show how the important kinds of plant work are provided for in the simplest way. They are, in fact, a simple introduction to the study of plants. 9. Water as a medium. — If Alga? are the primitive plants, it follows that the plant kingdom began in the water, for Algae grow in water or in very ^ moi_st_places. It seems to be true, also, that the most primitive Algae, as well as those that gave rise to the higher plants, lived in fresh water ; so that the numerous Algae that live along the sea- coasts are not the most primitive, nor have they given rise to higher plants. From this point of view, it follows that the fresh water Algae are the most important to study. 8 THALLOPHYTES 9 To live in water as a medium means that all the structures and habits of such plants must be adjusted to water. Such plants can be explained only by remembering this fact. That plants living in the water may be relatively simple is illustrated by the fact that when plants live in the air they must be protected against drying, and this in- volves protective structures that water plants do not need. 10. The cell (Fig. 1). — The living substance of plants and animals is called protoplasm. It is the only sub- stance that lives and works, and all the structures and work of plants are results of the activity of pro- toplasm. This protoplasm is organ- ized into definite units, which may be thought of as protoplasm indi- viduals, and these units or individuals are the cells. The simplest plants are single cells, while large and com- plex plants consist of millions of cells. It is in this sense that a cell may FlG- 1. — Ceiis.of a moss leaf: in each of the two be called the unit of structure, and that a plant consisting of one such unit may be regarded as the simplest kind of plant. Since a cell always includes sub- *. stances that are not protoplasm, the term protoplast is used to indicate the living substance of the cell. The protoplast, therefore, is the living, individual unit, and protoplasm is the material of which it is composed. We shall use the term protoplast, therefore, for the living, protoplasmic individual. Among plants, the semifluid protoplast usually sur- C rounds itself with a wall (Fig. 1). This cell-wall is com- posed of material called cellulose, which is manufactured complete cells the single large nucleus is seen, the numerous chloroplasts, and the granular-looking cytoplasm ; the cell-wall surrounding each cell is very distinct. 10 ELEMENTARY STUDIES IN BOTANY by the protoplast, and which forms a delicate but tough and elastic layer. The protoplast within its cell-wall is a very complex structure, which does a great variety of work. There are always at least two distinct regions or organs of the pro- toplast, which differ in appearance and in work. The ^\ nucleus is usually a globular mass of protoplasm (Fig. 1), lying in the midst of the protoplast, and marked off sharply by a delicate investing membrane. It is impossible to tell all that the nucleus does, but it is conspicuous in the work of cell-division, that is, the process by which a cell divides and forms two new cells. The remainder of the body of the protoplast, in which ^ the nucleus lies imbedded, is called the cytoplasm. -It" must not be thought that the cytoplasm is just a mass of pro- toplasm around the nucleus, for it has a structure of its own, and is especially conspicuous in the general processes of nutrition, which means the chemical and physical processes that take place in connection with the use of food. In green plants, such as the Algae, there is a third organ C of the protoplast, called the chloroplast (Fig. 1). Chloro- plasts are protoplasmic bodies of various forms among the Algae, but among the higher plants they are usually more or less globular. There may be a single chloroplast in a cell or there may be several chloroplasts, and they are dis- tinguished from the nucleus or from any other body in the cell by their green color, a color due to the presence of a green stain called chlorophyll. The peculiar work of the chloroplasts is to manufacture food from raw material, the details of which are outlined in the next chapter. A very important fact to know in reference to the cell is that the pj*otoplast is saturated with water when active. The water accumulates in the protoplasm, until the cell swells and the wall becomes stretched and tense. This swollen condition of the cell is called turgor, and it is one THALLOPHYTES 11 of the conditions necessary for its activity. Anything that withdraws water from the cell diminishes its activity, and if the loss of water continues, the protoplast becomes in- active and may pass into the condition called dormancy. In seeds, for example, the protoplasts may remain in this dormant condition for a long time, and then become active again when water is restored. 11. Work of the cell. — The work of the cell has been referred to in describing its parts, but it is important to emphasize it. The work of a plant of many cells is simply the sum of the work of all its cells. The work done by a living cell is so complex that it may be analyzed under several heads, but all of it may be grouped under two heads. One is the work of nutrition, which includes everything that has to do with the securing and using of food. It is by this work that a plant maintains itself in vigor and in growth. The principal part of the body of a complex plant is concerned with the work of nutrition, and this part is called the nutritive or vegetative body of the plant. The other kind of work is reproduction, which includes everything that has to do with producing new plants. In most plants the reproductive structures form a relatively small part of the body, but in one-celled plants or in simple many-celled plants nutrition and reproduction are carried on by all the cells. 12. The vegetative body of Algae. — Algae may be ar- ranged in a series, beginning with those having the most simple bodies, and advancing to those having the most complex bodies. In this way one can appreciate the prog- ress made by the plant body, and also the amount of such progress made by the Algae. For the sake of clearness, we may think of the bodies of Algae as representing different stages of general progress. The first stage is represented by those Algae whose bodies are single cells. Such plants are represented in the illustra- 12 ELEMENTARY STUDIES IN BOTANY tions by Pleurococcus (Fig. 2), very common as green patches on damp tree trunks, old board fences, damp walls and rocks, etc. When material from these patches, which often look like green stains, is observed under the mi- croscope, it is discovered to be made up of innumerable green, spherical cells. The figure referred to (Fig. 2) shows a sin- gle individual and also the suc- cessive divisions that result in groups of individuals. In every case, each cell is a separate plant, quite independent of all the rest. In each plant (cell) shown in the figure the nucleus may be seen, surrounded by the granular-look- ing cytoplasm, and this in turn invested by a wall. It is evident that these minute individuals are equipped to do the work of nu- trition and of reproduction just as truly as are the larger plants. A second stage is represented by those Algae whose bodies are also single cells, but the cells cling FIG. 2. — Pleurococcus; in the up- per left-hand corner is a single plant (one cell), with its nu- cleus and cytoplasm surrounded by a cell-wall ; in other figures the cell has divided, and has given rise to loose, irregular groups, in which each cell is an . independent individual, and together in such definite groups Jhe^eslr0"168 separated from that the groups are called colo- nies. Examples of such plants are shown in Figs. 3 and 4, In Fig. 3 (Gkeotfyece) , the cells, as they are formed, are held together in a more or less irregular colony by a mucilage that is developed from the cell- wall material (cellulose). In Fig. 4, two- colonies are shown: Nostoc (A), with the cells (individ- uals) held together in a definite row, so that the colony resembles a string of beads, and the mucilage is so abundant that many such colonies may be imbedded together in a single THALLOPHYTES 13 jelly-like mass; and Gloeotrichia (B), with its cells arranged as in Nostoc, but showing that the cells are becoming dif- ferent, so that the base and apex of the colony are not alike. Gloeothece (like Pleurococcus) is found in bluish green patches on tree trunks, fences, walls, etc. ; and Nostoc occurs as small lumps of jelly in damp places. In these colonies the cells (individuals) are held together mechanically by the mucilage, but they seem to be as independent as if they were separate. In the case of other colonies, such as the one shown in Fig. 5, the cells are much more closely related, being pressed against one another so as to flatten the walls that are in contact. Although the cells of this colony (Oscil- latoria) are for the most part in- dependent of one another, as shown by the fact that they may break apart and live inde- pendently, they work together in , certain ways, notably in the char- acteristic swaying and revolving movements of the colony as a whole, movements that have given name to the plant. This interesting plant forms bluish green slippery masses on wet rocks, or it occurs on damp soil or freely floating on the water. When the individual cells of a colony work together in a still more intimate way, the colony of many individuals be- comes the individual of many cells. This many-celled in- dividual is the third stage in the progress of the plant body, and it is evident that there is no way of telling just when a colony becomes such an individual. The three general stages, therefore, are (1) the single cell, (2) the colony, (3) the many-celled individual. All of the remaining FIG. 3. — Glceothece: in the upper left-hand corner is a single plant (one cell), with its nu- cleus, cytoplasm, and wall, and also a covering of mucilage de- veloped from the wall-material (cellulose) ; in the other figures, successive divisions are shown, resulting in an irregular colony of individuals held together by the investing mucilage. 14 ELEMENTARY STUDIES IN BOTANY illustrations of the Algse show examples of many-celled individuals. The bodies of many-celled Algse have different forms, which may be referred to three general heads. It has been stated that cells divide. This is too complicated a process to describe here, but in general it means that the nucleus FIG. 4.— Nostoc (A) and Gloeotrichia (B) : the colony has the form of a beaded filament, imbedded in a mucilage sheath ; in B the cells at the base of the colony are much larger than those above, showing that the individual cells are be- ginning to differ. FIG. 5. — Oscillatoria : a> very compact fila- mentous colony, in which the cells work together to produce the oscillating move- ment of the colony. divides first and that a new wall is laid down between the two nuclei and extends through the cytoplasm to the old wall, making two cells half the size of the original one, just as a partition run through a room divides it into two smaller rooms. The new cells differ from the new rooms, however, in growing until each one is as large as the old cell. THALLOPHYTES 15 FIG. 6. — Coleochcete: a flat, plate-like body; from such an alga body the land plants were probably de- rived. In the first place, the cells composing the individual may divide freely in every plane, and this results in a massive body. This form is not very common among Algae, because it is not the most favor- able arrangement of cells for free ex- posure to water. In the second place, the cells com- posing the individual may divide chiefly in two planes, at right angles to one another, and this results in a flat, plate- like body, which may be a single layer of cells in thickness, or several layers (Fig. 6). This form of body is more favorable for water exposure than the massive form, but it is not the most favorable. In the third place, the cells composing the individual may divide only or chiefly in one plane, or rather in a series of parallel planes, and this results in a fil- amentous body (Figs. 7, A, and 8). This is by far the most common form of body among the Algae, especially the fresh-water forms, and it permits not only every cell to come into contact with water freely, but also the free swaying movements that are of advantage in water. Another tendency in many-celled plants, which results in FIG. 7. — Ulothrix: A, base of filament, showing the holdfast cell and five of the ordinary cells above ; B, four cells of a filament containing spores ; C. showing one cell (a) containing four swimming spores, a free swimming spore (6), four escaped gametes (c), pairing gametes (d), and two oospores (e) each of which has been produced by the fusion of two gametes ; Z>, a young filament started by a swimming spore. 16 ELEMENTARY STUDIES IN BOTANY the development of increasingly complex bodies, is for the cells to become unlike. This tendency to become different FIG. 8. — Cladophora: a branching fila- ment, each of whose cells contains several nuclei ; in two of the cells swimming spores have devel- oped, and from one of the cells some of the spores have es- caped, showing the pair of cilia. FIG. 9. — Laminar ia : a common kelp, show- ing a complex body differentiated into holdfast, stalk, and blade (leaf-like por- tion). is called differentiation. For example, in the filamentous body of Ulothrix (Fig. 7, A) the lowest cell differs from all FIG. 10. — Macrocystis: a kelp with very long and rope-like stem bearing nu- merous blades. — After BENNETT and MURRAY. THALLOPHYTES 17 the rest in size and form and contents, and serves as a hold- fast for anchoring the plant. This anchoring cell is found in a great many filamentous forms, and shows that differentiation of form, etc., has to do with difference of work. Among the marine Alga3 this differentiation be- comes very great. For example, in such seaweeds as are illustrated in Figs. 9 to 14, there are complex holdfasts (often looking like roots), stalks (resembling stems), and leaf-like portions (which may just as well be called leaves). In these cases, not only is the body differ- entiated into dif- ferent regions, but the cells composing each region are dif- ferentiated. To summarize these statements in reference to the vegetative bodies of AlgaB, it may be said that the Algae begin as one-celled plants and become many-celled plants ; that the cells of the many-celled forms become differ- entiated ; and that finally the many- celled body becomes differentiated into different regions. 13. Reproduction. — The preceding sections give an account of the vege- tative body of Algae. It now remains to consider the methods of reproduc- tion developed by the Alga?. It must be understood that reproduction began as a relatively simple process, and that it became gradually more and more com- FIG. 11. — Nereocystis : a bladder kelp, show- ing the blades arising from the bladder-like expansion of the end of the stalk. FIG. 12. — Fucus: fragment of rockweed, showing the forked branching, the swollen tips in which the sex-organs are produced, and the air bladders (three of them near the base). 18 ELEMENTARY STUDIES IN BOTANY plex, and therefore that there has been an evolution of re- production. It must not be supposed that reproduction always became more complex as a vegetative body became more complex, for comparatively simple bodies may show an advanced method of reproduction, and many complex bodies have retained a relatively simple method of reproduc- tion. In general, however, as plants advanced in the struct- ure of their bodies, they advanced also in the methods of reproduc- tion. 14. Vegetative multiplication. - In the simplest plants, notably the one-celled forms, new individ- uals arise by dividing the old ones. For example, a one-celled indi- vidual works for a time as a vege- tative body (engaged in the work of nutrition), and then the cell divides, producing two new indi- viduals (Figs. 2 and 3). Since this kind of reproduction involves only vegetative cells, it is called vegetative multiplication, which means that it is simply a method of multiplying vegetative cells. When these multiplied vegetative cells are new individuals, the process becomes a kind of reproduction. This seems to have been the first kind of reproduction among plants, and in many groups it is still the only kind of reproduction. Any group that has no other method of re- production is regarded as one of very low rank, for the method of reproduction among plants is regarded as more important in ranking them than is the structure of their vegetative bodies. It must not be supposed that vegetative multiplication occurs only among the lowest plants, for it is found in all groups of plants, even the highest. For example, when FIG. 13. — Sargassum: fragment of gulfweed, showing differen- tiation of the body into stem, leaves, and bladder-like floats (resembling berries). THALLOPHYTES 19 potatoes are planted, the tuber, composed of vegetative cells, is cut into pieces, and each piece can develop a com- plete new plant. The leaves of some plants can be used in the same way ; grapevines are usually started by planting " cuttings " or " slips " (bits of stem) ; and the process of "grafting" fruit trees really means starting new individuals FIG. 14. — One of the Red Algae, showing a very much differentiated and complex body. from vegetative structures. When a new method of repro- duction appears among plants, therefore, it does not mean that the old method is dropped, but that the new one is added. A very important fact in reference to vegetable multi- plication remains to be stated. When the cell of a one-celled plant divides, the result is two new individuals; but when 20 ELEMENTARY STUDIES IN BOTANY a vegetative cell of a many-celled plant divide's, the result is usually the addition of new cells to the body, so that there are no new individuals, but the old individual grows. In other words, the cell- division which results in reproduction among one- celled plants usually re- sults only in growth among many-celled plants. In a certain sense, any such growth is reproduction, for new cells are produced, but we are using the word re- production in the sense of producing new individuals. FIG. 15. — (Edogonium: A, part of a filament, one of whose cells has formed a single large swimming spore with a crown of cilia ; B, part of a filament showing antheridia (a) from which two sperms (b) have escaped, a vegetative cell with its nucleus, and an oogonium (the large round cell) filled by a large egg packed with food and whose nucleus is seen (d) , and which a sperm has entered (c) ; C, a swimming spore with its crown of cilia ; D, a young plant developing from the swimming spore. It is quite evident, therefore, that this process of cell- division goes on in all plants, and that in the lowest it is the only method of reproduction. THALLOPHYTES 21 15. Spore-reproduction. — The second method of re- production that appears among the Algae is reproduction by spores. A spore is a special reproductive cell, as distinct from a vegetative cell. For example, in such a form as Ulothrix (Fig. 7), the vegetative body is a filament of cells (A). These cells perform the ordinary vegetative work of green cells when the con- ditions favor such work ; but if the conditions change, they may begin to form spores (B and C) . The protoplast that has been doing vegeta- tive work divides, and this division may be fol- lowed by others, until the wall of the old vege- tative cell incloses a number of new cells, which are the spores. The spores escape from the old inclosure into the water, and in Ulothrix they swim freely about by means of a tuft of four cilia (hairs) at the tip of each spore (C, 6). These " swimming spores " are very characteristic of the Algse, but the number and arrangement of the cilia vary. For example, in (Edogonium (Fig. 15, A and C) the cilia occur as a crown at one end ; in the brown seaweeds there is a pair of cilia on one side of the spore (Fig. 16) ; in certain forms there is a single cilium ; while the most common con- dition is a pair of cilia at the apex of the spore (Fig. 8). It must not be supposed that spores are necessarily ciliated, 3 FIG. 16. — Ectocarpus : A, part of a filament showing a sporangium distinct from the vege- tative body, and also an escaped swimming spore (enlarged) with its two lateral cilia ; B, part of a filament showing a gametangium distinct from the vegetative body, and also an escaped gamete with its two lateral cilia. 22 ELEMENTARY STUDIES IN BOTANY for spores of the Red Algge, for example, have no cilia (Fig. 17) and are carried about passively by the water, while the .spores of higher plants are carried through the air. Nor must it be supposed that spores are necessarily produced by the division of a protoplast; they generally are, but sometimes the whole protoplast escapes from its investing wall and is a spore (Fig. 15, A). Nor is a spore always naked (without a wall). Although swimming spores are usually naked, spores exposed to the air have walls, and sometimes very heavy walls. A spore is recognized, there- fore, not by its cilia, its form, its covering, or its origin, but simply from the fact that it is able to produce a new plant. The process by which a spore starts a new plant is called germination, so that the business of a spore is to germinate. In most of the Alga3, spores are produced by the ordinary vegetative cells, that is, by cells that are a part of the vegetative body and form spores only when the conditions for vegetative work become unfavorable. Gradually, among the Alga3, however, the cell that produces spores becomes more and more distinct from the other cells, until finally it is entirely distinct, doing no vegetative work, and only producing spores, as in the brown alga shown in Fig. 16 and in the red alga shown in Fig. 17. Such a cell is called a sporangium, which means " spore-case." Although Alga3 are characterized by an abundant formation of spores, it is only among the higher groups of Algae that sporangia become differentiated from the rest of the body. FIG. 17. — Portion of a red seaweed, show- ing a sporangium with its four spores (A), and another one (B) from which the spores (with no cilia) have escaped. THALLOPHYTES 23 16. Sex-reproduction. — A third method of reproduction appears among the Algae, and it represents the final stage in the progress of reproduction. This method was derived from spore-reproduction, and some of the Algae illustrate this fact completely. In Ulothrix (Fig. 7, B and C), for example, a number of spores are produced by a single protoplast, the number of spores depending on the number of successive divisions. Naturally, the more numerous the divisions are, the smaller are the spores, so that in Ulothrix the number and size of the spores vary with the number of divisions. It is found that the smaller spores produce feebler plants, and that the divisions may become numerous enough to result in spores too small to produce plants at all. Under these circumstances it is observed that these small and incapable spores may pair with one another and fuse to form a single cell (Fig. 7, C, d and e), and that this cell can produce a new plant. This act of fusing, by which a reproductive cell is formed, is the sexual act, often called fertilization; the two fusing cells, which are no longer spores because they cannot pro- duce new plants alone, are sexual cells, usually called gametes; and the resulting cell with reproductive powers is an oospore, sometimes called the fertilized egg. It is evident that gametes, among Algae, are derived from swimming spores, and that the changes by which a swimming spore becomes a gamete are the changes that explain the origin of sex. It is also evident that the oospore is a spore, because it produces a new plant, but it differs from the ordinary spore in the method of its origin. It is for this reason that it is distinguished by a pre- fix that means " egg," implying that it has been produced by the sexual act. When the word "spore" is used, the ordinary reproductive cell, not produced by the fusion of two cells, is meant. Very often the phrases " asexual spores " and " sexual spores " are used to distinguish these two kinds of spores, but the latter phrase is misleading, for 24 ELEMENTARY STUDIES IN BOTANY no spores are "sexual," the only sexual cells being the gametes. Spores and oospores are not produced by Algae continu- ously, for under certain conditions Algse may vegetate, with- out producing any spores ; under other conditions they may produce spores freely; and under still other conditions gametes appear and oospores are formed. In the ordinary course of the seasons, the spores are produced during the growing season and multiply individuals, in fact they do most of the reproduction. The gametes, on the other hand, usually appear towards the end of the growing season for the plant, and so the formation of the oospores is about the last activity of the plant. The spores germinate at once, but the oospores, appearing late in the season, develop heavy walls, remain dormant through the winter, and ger- minate at the beginning of the next growing season. In such plants, therefore, the oospores are the only structures that remain alive through the winter. It may be said, therefore, that spores multiply the plant, while oospores protect it through the winter and start it again. In those Algse in which there is no sex, and therefore no oospores, ordinary vegetative cells become heavy-walled and protect the plant through the winter. 17. Life-history formulae. — The life-history of a plant means the complete history of its life, beginning at any point, for example, the spore, and continuing until spores appear again. It is helpful to express the outlines of a life-history by a formula, and the following formulae illustrate the life- histories of the Algse we have been considering. Vegetative multiplication may be indicated by P — P — P, etc., in which " P " stands for " plant," and which indicates that one plant produces another directly, without any special cells. Spore- reproduction may be indicated by P— a — P — o — P — o, etc., which indicates that the plant produces a spore which pro- duces another plant, and so on. Sex-reproduction may be THALLOPHYTES 25 indicated by P=J>o — F~°>o — P, etc., which indicates that the plant produces two gametes which fuse to form an oospore which produces another plant, and so on. It must be remembered that in plants that produce sexual cells, all three ways of producing new plants are found, so that a real life-history formula for such a plant would be something as follows : -P This simply indicates the three methods of producing new plants. 18. Differentiation of sex. — At the first appearance of sex, the gametes are alike in form and behavior, as in Ulothrix (Fig. 7, C, d}. They are approximately the same in size, and are both swimming cells with the same arrangement of cilia, so that there is no visible sex-distinction. Plants with such gametes are sometimes called " unisexual plants," which means plants having only one sex. The phrase is misleading, for to have sex at all, there must be two sexes. What the phrase really means is that the sexes cannot be distinguished. In other plants, however, the pairing gametes begin to show differences, one being larger than the other and cor- respondingly less active, until finally one is relatively very large and entirely passive, while the other retains its small size and activity. The increased size of one of the gametes means an increased nutritive power, but this gain has been accompanied by a loss of swimming power. This develop- ment of obvious differences between the pairing gametes is the differentiation of sex, whereby the two sexes become apparent. The large and passive gamete is female, and is called the egg; while the small and active gamete is male, and is called the sperm. For example, the illustration of (Edogonium (Fig. 15, B) shows a large egg (packed full of 26 ELEMENTARY STUDIES IN BOTANY food) within a swollen cell, and small ciliated sperms having escaped from small cells (6) ; while the illustration of Fucus (Fig. 20) shows a very large egg surrounded by numerous, small, and very active sperms. 19. Differentiation of sex-organs. - - In such Algae as Ulothrix (Fig. 7, C), an ordinary vegeta- tive cell, without any change of form, produces gametes. In other Algae, as Ectocarpus (Fig. 16, E), the cells that produce gametes differ in form from the vegetative cells, just as the cells that produce spores (A) differ from them. Just as the spore-producing cells that become different from the vegetative cells are called sporangia (§ 15, p. 22), so these gamete-producing cells that become differ- ent are called gametangia (" gamete -cases")- A gametangium, therefore, Vocc J.' ig» JL&J uvjuuaaj-ung u 10,11. unco jjn_m.u.Sf FIG. 20. — Fucus: A, the eight eggs discharged from the oogonium; B and C, egg surrounded by swarms of swimming sperms. — After STRASBURGER. connected by tubes, and all of the cells of one filament empty, which means that all of the gametes of one filament have passed over into the cells of the other filament. If the FIG. 21. — Vaucheria: A, part of a filament, showing the special branches producing an antheridium (a, emptied in this specimen) and an oogonium (fc) ; B, another species, in which a single branch bears several oogonia and a terminal coiled antheridium. THALLOPHYTES 29 active gametes are male, then the emptied filament is a male individual, and the receiving filament is a female individual. In such a case, there- fore, there is a sexual differentiation of indi- viduals, and in Spiro- gyra this occurs with- out any differentiation of gametes in appear- ance, and without any differentiation of sex- organs. After the origin of sex, therefore, when the formation of gam- etes is an established habit, there are three kinds of differentia- tion : differentiation of gametes, of sex- organs, and of sex- individuals. These different kinds of dif- ferentiation may occur singly, or any two to- gether, or all three to- gether. When the last takes place, and we find plants with eggs and sperms, produced by distinctly set apart oogonia and anther- idia, and these two kinds of sex-organs borne on different individuals, we have reached an extreme case of sexual differentiation. FIG. 22. — Spirogyra: A, part of a filament, show- ing one complete cell, with its central nucleus and its characteristic chloroplast (the spiral band) ; B, cells of two filaments developing the connecting tubes ; C, the passage of one pro- toplast through the tube ; D, the oospore formed by the fusing of the two protoplasts; the emptied cell is therefore male and the cell containing the oospore is female, and if all the cells of each filament are like the one shown, the filaments (individuals) are male and female. 30 ELEMENTARY STUDIES IN BOTANY 21. Summary. — Algae represent the beginnings of the plant kingdom, and all their structures are related to water as a medium. The simplest body is a single cell, but among Algae the body advances from the single cell, through cell-colonies, to the many-celled individual, whose form is prevailingly filamentous, although other forms occur. Among the higher Algae, the many-celled body often becomes differentiated into different regions, notably among the marine Algae. The simplest form of reproduction is vegetative multipli- cation. In addition to this, Algae developed reproduction by means of spores, which in most cases are swimming cells. Among the Algae there appears also sexual reproduction, at first the gametes seeming to be alike, then differentiating into sperms and eggs. The two kinds of gametes at first are produced by ordinary vegetative cells, but later special cells produce them, which are therefore sex-organs. CHAPTER III FOOD MANUFACTURE 22. Peculiar work of green plants. — The Algae differ from other Thallophytes in containing chlorophyll (§ 10, p. 10). The presence of this pigment is so common among plants that vegetation is thought of as being green, but very many plants are not green. Even those that contain chlorophyll are not always green in appearance, for this pigment may be obscured by others. For example, there are four groups of Algae that are distinguished by their color, although all of them contain chlorophyll. The two conspicuous groups of fresh-water Algae are called " Blue-green Algae " (Cyano- phycece) and "Green Algae" (Chlorophycece) because in the former a blue pigment is associated with the green, giving the plant a bluish green tint, and, in the latter, chlorophyll is the only pigment. The two conspicuous groups of marine Algae are called " Brown Algae " (Phceophycece) and " Red Algae " (Rhodophycece) because in the former certain brown and yellow pigments are associated with the green and often mask it completely, and in the latter a red pigment obscures the green. The presence of chlorophyll in the Algae gives them a peculiar power among Thallophytes, a power that all green plants possess. It is the power of manufacturing food. It is perhaps impossible to define exactly what is meant by food, but in general it means material that protoplasm can use in building up its body. All living things must use food, but only green plants can make it. This process, therefore, is one of the very greatest importance, for the existence of all plants and animals depends upon it. 31 32 ELEMENTARY STUDIES IN BOTANY Substances are said to be either organic or inorganic. An organic substance is one that is made by a living body ; an inorganic substance is one that is usually made quite inde- pendently of a living body, as air, water, compounds in the soil, rock material, etc. The manufacture of food consists in taking these inorganic substances and making from them organic substances. It is this that green plants are able to do, and they manufacture food not only for their own use, but also for the use of plants that are not green as well as for the use of all animals. The food used by plants does not differ from that used by animals ; the difference is that green plants have the added power of manufacturing food. A miller uses flour for his bread, just as every one else does, but he differs from others in also being equipped to manu- facture his flour. There are several general kinds of food, but the peculiar work of green plants has to do with only one of them, the kind called carbohydrates. If this name does not happen to suggest any kind of food, such common carbohydrates as sugar and starch will make the kind clear to every one. The importance of the manufacture of carbohydrates, which is the peculiar work of green plants, is recognized when it is known that in the manufacture of the other foods carbohy- drates must be used. This means that although carbohydrates are not the only kind of food, they are the necessary start for all other kinds. 23. The raw material. — It is important to know the inorganic substances a green plant uses in the manufacture of carbohydrates. They cannot be rare substances, or vegetation would not be so common. They are water and carbon dioxide. The former needs no explanation; the latter is often called " carbonic acid gas," and is the so- called " impure " gas that accumulates in badly ventilated rooms. Carbon dioxide is everywhere in the air, in very small proportion (about three parts in 10,000), and is more FOOD MANUFACTURE 33 abundant in quiet waters, in which it is dissolved not only from the air, but also from the breathing and decay of the innumerable plants and animals that live in water. The Algae naturally obtain it from the water in which they are living; while plants living on land obtain it from the air, chiefly through their leaves. The Algae need no special equipment for obtaining water, for their bodies are exposed to it and it enters all the cells freely ; but in the case of land plants, the special equipment is usually a root system into which water enters from the soil. An important feature of these two substances that the green plant uses in carbohydrate manufacture, is that they are what are called " ultimate wastes " when food is being used. This phrase means that in our bodies, for example, carbon dioxide and water are disposed of because the body does not use them, and it does not use them because they are so difficult to break up as preliminary to forming new combinations. The ultimate wastes of living bodies, there- fore, can be used by green plants as the raw materials for the manufacture of food. From food to waste is the work going on in all living bodies ; from waste to food is the added work going on in all green plants. 24. The agent. — The active agent in the manufacture of carbohydrates is the (ihloroplast (§ 10, p. 10, and Fig. 1). As the name implies, a chloroplast consists of two conspicu- ous substances: (1) the living protoplasm (plastid), and (2) the green pigment (chlorophyll). They can be separated from one another by soaking green parts (as leaves) in alcohol, which extracts the chlorophyll and leaves the plastids color- less. Just what each of these substances does in the manu- facture of carbohydrates is not known with certainty, but it is certain that both are necessary. The plastid is alive and the chlorophyll is not, but since the manufacture of carbohydrates is a chemical process, the chlorophyll may be the cause of some of the changes. In fact, a chloroplast 34 ELEMENTARY STUDIES IN BOTANY may be thought of as a chemical laboratory, which uses cer- tain substances in the manufacture of others. 25. The energy. — Those who have studied physics are aware that energy, the power for work, is as real a thing as the material to work with. It is important, therefore, to discover the source of the energy used in the manufacture of carbohydrates. The chloroplast obtains this energy from sunlight, and it is known that chlorophyll is able to absorb energy from light. It is evident that this absorbed energy, in some form, is used in the chloroplast. It follows that carbohydrates can be produced by green plants only when exposed to the light, and that at night the process is suspended. In fact, many green plants may live through the winter, in the form of bulbs, tubers, etc., without any opportunity to manufacture food. It must be evident, therefore, that a process which is suspended for a consider- able period during every twenty-four hours, and that may be suspended for months, is not a process of living, which involves the use of food, for living must go on continuously. It is simply a manufacture, which has nothing to do with the process of living except that it provides the material that is used in the process of living. It holds the same relation to the process of living that the baker holds to us in manufacturing bread. It is important to observe that light is essential not only to the manufacture of carbohydrates, but also to the manu- facture of chlorophyll itself. If light is withdrawn from a green plant for a considerable period, the plant loses its green color, as when a board lies for some time upon the grass, or when earth is heaped about celery to blanch it. When potatoes " sprout " in a dark cellar, the young shoots are pallid, but if exposed to light they become green. 26. The process. — The manufacture of carbohydrates by green plants has received a name suggestive of the process. It is called photosynthesis, which means putting together in the FOOD MANUFACTURE 35 presence of light. The word " photograph" shows the same use of the word light, and the process of " photography " shows the same activity of light in causing chemical changes. The first step in the process seems to be the " breaking up " of the water and carbon dioxide into their constituent ele- ments. Those who have studied chemistry know that water is a combination of the two elements hydrogen and oxygen, both of them gases, in the proportion of two parts of hydrogen to one part of oxygen, so that the formula for water is H2O. Carbon dioxide is also a combination of two elements, carbon and oxygen, and its formula is C02. To break up these two substances, so that the water splits into the two gases that compose it and the carbon dioxide splits into the gas and the solid that compose it, is a process that requires a great dis- play of energy, in the form of heat, electricity, etc., when done in the laboratory ; but it is accomplished by the green plant without any unusual display of energy. Following the breaking up (analysis) of the raw materials, the elements are put together in new combinations, the " putting together " being the " synthesis " referred to in the -name photosynthesis. It must not be supposed that a carbohydrate is the result of the first synthesis, for it is reached only after a series of chemical changes. 27. The product. — The final product of photosynthesis is reached when a carbohydrate is formed. If the raw ma- terials and the final product are compared, certain important facts become evident. The simplest method of comparison is to use the following equation : C02 + H20 = QHaO + O2. The first side of the equation represents the raw materials, and the other side represents the carbohydrate product and the oxygen left over. CH20 is not the formula for a car- bohydrate, but it may be called the carbohydrate unit, which by using various multiples becomes the formula of various carbohydrates. For example, a simple carbohydrate is C6Hi2O6, in which 6 is the multiple, and most other carbo- 36 ELEMENTARY STUDIES IN BOTANY hydrates are multiples of 6. In examining the second hall of the equation, it becomes evident (1) that the carbohydrate contains hydrogen and oxygen in the same proportion as in water, a fact which gives name to the compound (" carbohy- drate " means carbon and water) ; and (2) that oxygen is freed as a waste product (or by-product) in the same propor- tion as it exists in carbon dioxide. The total result is to get the carbon out of the carbon dioxide and combine it with water, and therefore the process is often called the " fixation " of carbon. Hydrogen and oxygen are gases, so that carbon is the only solid that enters into the fabric of the plant, and this solid is obtained from a gas that exists in the air. The carbohydrates thus formed in the plant are usually starches or sugars, and they are freely transformed into one another. It is often stated that green plants form starch, but the fact is that starch is only the visible form of the carbo- hydrate. It is visible because it does not dissolve in the cell sap, while sugar is invisible because it does dissolve. When more carbohydrate is manufactured than is being used, it becomes stored up in the form of starch, and therefore starch is spoken of as the storage form of a carbohydrate. On the other hand, when the carbohydrate is being used and is being carried around through the plant, it is in the form of sugar, for a substance must be in solution to be carried about, and therefore sugar is spoken of as the transfer form of a carbohydrate. 28. The by-product. — It has been noted that during photosynthesis oxygen is given off as a by-product. Nothing more than a statement of this fact would be needed if it were not connected with a persistent misconception in reference to photosynthesis. When it was first observed that green plants take in carbon dioxide and give out oxygen, it was natural to suppose that this gas exchange represented the respiration of plants. Since the gas exchange in the respira- tion of animals is just the reverse (taking in oxygen and giving FOOD MANUFACTURE 37 out carbon dioxide), the opinion became current that plants and animals differ in their " breathing." As a corollary to this opinion, it was pointed out that animals and plants supplement each other in this process, each taking in what the other gives off, and each living on what the other rejects. Since this impression is still current, its correction must be emphasized. It is clear that photosynthesis has nothing to do with respiration, for respiration is associated with what may be called the act of living, and therefore is carried on by every living thing. If respiration stops, the plant or animal body is dead; in fact, we use respiration as an evidence of life. Therefore plants and animals " breathe " alike, both taking in oxygen and giving out carbon dioxide ; but green plants can carry on the process of photosynthesis also, in connection with which it takes in carbon dioxide and gives out oxygen. The confusion arose from the fact that during the day, when photosynthesis is going on, the amount of the gas exchange involved in the manufacture of carbohydrates is so much greater than the amount involved in respiration that the latter was not noticed ; but if the observation had extended into the night, it would have been discovered that only the gas exchange of respiration was being carried on. It may be useful to contrast photosynthesis and respira- tion sharply as follows : photosynthesis occurs only in green cells, requires light, uses carbon dioxide, liberates oxygen, makes organic material, and accumulates energy; while respiration occurs in every living cell, does not require light, uses oxygen, liberates carbon dioxide, uses organic material, and uses energy. 29. Manufacture of proteins. — Carbohydrates are by no means the only foods, and 'therefore photosynthesis is not the only process of food manufacture. Another conspicu- ous group of foods is the proteins, which may be regarded as foods in the most advanced stage, since the living proto- plasm is largely composed of proteins. Carbohydrates, 4 38 ELEMENTARY STUDIES IN BOTANY therefore, may be thought of as the first stage of food, and proteins as the last stage. The constitution of proteins is not known, so that their manufacture is not understood. It is known that neither light nor chlorophyll is required, for the process goes on in living cells removed from light, and in plants containing no chlorophyll. It is known, however, that carbohydrates are used, and that to the carbon, hydrogen, and oxygen supplied by them, the elements nitrogen, sulphur, and often phos- phorus are added. It is important to know the sources of these new elements that enter into food manufacture. They are not used by the plant as free elements, but are obtained from their combinations in what are called salts. For ex- ample, salts containing these elements occur in all soils upon which plants can grow, and these same salts are dissolved in the water in which AlgaB grow. In land plants, they enter through the roots, while in Algae they enter wherever the plant is exposed to water. 30. Assimilation. — While the processes of food-manu- facture are being considered, it will be helpful to define the use of food. There is an intermediate process called digestion, which simply means the conversion of foods into transfer forms, usually soluble forms. For example, digestion trans- forms insoluble starch into soluble sugar. It is evident, furthermore, that only those foods need to be digested which are not in transfer form. The process by which foods are used in the manufacture of protoplasm is called assimilation. Protoplasm is the living body and it uses food to construct more protoplasm. 31. Respiration. — Everything about the plant is a pro- duct of protoplasm, and in doing the great variety of work that goes on in a living body the protoplasm " breaks down," using itself up continually in the manufacture of products. Of course this explains why it must be assimilating all the time, so that its body may be continually built up. This FOOD MANUFACTURE 39 process of breaking down the protoplasmic body is respira- tion, and one of the superficial indications that respiration is going on is that oxygen is taken in and carbon dioxide is given off. This gas exchange, therefore, is not respiration, but is merely the external evidence that the process is going on. 32. Summary. — The peculiar work of green plants is to manufacture carbohydrates. The raw materials used are carbon dioxide and water, which the chloroplasts, with energy obtained from sunlight, use in the manufacture, a certain amount of oxygen being given off as a by-product. The car- bohydrates thus manufactured are the basis of other foods (as proteins). Water and carbon dioxide, therefore, are not foods, but materials from which foods are manufactured. The food of all plants and animals is the same, and when used it is digested (if necessary) and assimilated (built up into proto- plasm) ; and the evidence that the living protoplasm is working is that respiration is going on, an external indication of which is the entrance of oxygen and the escape of carbon dioxide. All plants and animals, therefore, use the same food and " breathe " in the same way, but only green plants can manufacture food from material that is not food. CHAPTER IV THALLOPHYTES — 2. FUNGI DEPENDENT PLANTS 33. The dependent habit. — The Algae are said to be independent plants because they can manufacture carbo- hydrates from inorganic material. This means that they do not depend upon any other plants or animals for their food supply, and therefore could live and work if they were the only organisms in existence. The Fungi, on the other hand, are those Thallophytes that have no chlorophyll, and there- fore cannot manufacture carbohydrates. This means that they must depend upon other plants and upon animals for their food supply, and that they could not exist in the ab- sence of green plants. It must not be supposed that Fungi are the only dependent plants, for even among seed-plants there are those without chlorophyll, as Indian pipe and a number of orchids, that are compelled to obtain their food from other organisms. But the Fungi represent by far the greatest assemblage of de- pendent plants. 34. Parasites and saprophytes. — If Fungi must obtain their food from other organisms, it should be recognized that there are two general conditions in which this food occurs. It is either a part of the living body of a plant or animal, or material that has been produced by a living body and is no longer connected with it. For example, when the rust fungus attacks wheat, it is obtaining food from living plants ; 40 THALLOPHYTES 41 but when a mold fungus attacks bread, it is obtaining food from material produced by living plants, but no longer con- nected with them. Fungi (like the rust) that attack living bodies are called parasites; while those (like the mold) that attack organic material no longer connected with a living body are called saprophytes. It must not be thought that parasite and saprophyte are terms of classification. They refer only to two sources of food supply, and there are many Fungi able to obtain food from both sources. Naturally, some Fungi are usually para- sites, and some are usually saprophytes, but they all obtain food from any available source. In fact, many so-called parasites do not attack the living cells of plants, but live in the vessels carrying water (" sap ") and thus choke them. It is convenient, however, in a general way, to distinguish between the parasitic habit and the saprophytic habit, for while the former often brings trouble to living plants and animals, the latter does not. The plant or animal attacked by a parasite is called its host, and when the attack interferes with the vigor of the host, the latter is said to be diseased. It is important to understand what is meant by disease, for there is often con- fusion in using the word. For example, rust is often spoken of as a disease of wheat and other cereals, when, in fact, rust is the parasitic fungus that induces the disease. The range of attack by parasites is extremely variable. For example, some parasites attack many kinds of plants; others attack only a certain family of plants ; others attack still smaller groups; and still others attack only one kind (species) of plant, and often can select that species with more certainty than does the botanist. Parasites differ also in the amount of the host attacked. For example, some attack the whole plant ; others attack only certain general regions (as shoots or flowers) ; while still others may be restricted to a single kind of organ. 42 ELEMENTARY STUDIES IN BOTANY 35. Economic importance. — It was said of Algae that they are of little or no economic importance, but of very great scientific importance in the history of the plant kingdom. This statement may be reversed for Fungi. They are of little scientific importance in the history of the plant king- dom, but of very great economic importance. In denning parasites, it was stated that they induce disease, and when it is realized that these plant parasites are responsible for many diseases that ravage crops, domesticated animals, and the human population, it would be hard to exaggerate their economic importance. It is on account of this importance that the parasitic fungi have received so much attention, for they represent an enemy against which men must always be on guard. On the other hand, the work of the saprophytes is often beneficial. They may be regarded as natural scavengers, decomposing dead bodies and organic waste into their con- stituent elements or inorganic compounds. Advantage is taken of this process in various manufactures, such as the manufacture of alcohol from sugars, the fermentation of fruit juices in the manufacture of wines, the " raising " of bread dough by yeasts, etc. 36. Origin of Fungi. — It is a common belief that Fungi are Alga3 that have lost the power of food-manufacture. Some Algae and Fungi resemble one another so closely in structure that this belief seems reasonable ; but most Fungi differ so much from all known Algae that such a connection does not seem convincing. It is easy to understand how Algae might lose the power of food-manufacture if exposed to an available food supply. For example, certain Algae inhabit cavities in the bodies of green plants, and the food manufactured by these plants might be available for the Algae, which might thus gradually become dependent. Perhaps the best reason for believing that Fungi are degenerate Algae is that probably the two groups existed THALLOPHYTES 43 together before any other plants appeared, and that under such conditions Fungi could not appear until after Algae FIG. 23. — Bacteria of various kinds, mostly ciliated ; F is the bacterium of typhoid fever, and H that of cholera. — After ENOLER and PRANTL. had started the business of food-manufacture. However, we know nothing of the history of plants before the Algae and 44 ELEMENTARY STUDIES IN BOTANY Fungi that we see, so that any statement as to the relation- ship of these two groups is at best a hypothesis that may or may not be true. 37. Bacteria. — One of the prominent groups of Fungi is called bacteria, a name that has become very familiar in connection with the study of human diseases, sanitation, etc. Once bacteria were spoken of as " germs of disease," and were often thought of as minute animals. It is impos- sible to overestimate their importance to man from the stand- Hit FIG. 24. — Some bacteria of fermentation and disease: bacteria of souring milk (A), of vinegar (£), of diphtheria (C), of tetanus or lockjaw (£>). — After FISCHER. point of his personal interest. It is this fact that has stimu- lated the study of bacteria to such an extent that it has become a special subject known as bacteriology. Bacteria include the smallest known plants, some of them being visible only under the highest powers of the micro- scope, and doubtless there are some that are even smaller, and have remained invisible. They are single cells (spheri- cal, oblong, rod-like, or curved), and occur either singly or held together usually in filaments (Figs. 23 and 24). Often they have cilia and swim freely, and this fact probably first suggested that they are minute animals. They occur every- where, in all waters, in air, in soil, in all plants and animals (living or dead). A striking feature is their power of en- during some conditions that would destroy other plants, as extremes of temperature, great dryness, etc. Their only THALLOPHYTES 45 method of reproduction is by means of vegetative multi- plication, but this multiplication proceeds with such remark- able rapidity that a single cell may give rise to millions of cells in twenty-four hours. Some of the important work done by bacteria may be outlined as follows. Some bacteria attack dead bodies of plants and animals, or organic material produced by plants and animals result- FIG. 25. — Diagram of Mucor, showing the profusely branching mycelium and three sporophores, one of which bears a sporangium. — After ZOPF. ing in what is called putrefaction or fermentation (Fig. 24, A and B). All of this work is of large service, but special use is made of certain of the fermentations, as already mentioned. Other bacteria attack living plants and animals, producing various diseases, which are regarded as important so far as they affect our cultivated plants, our domesticated animals, and ourselves. Many of the common and most dangerous diseases of the human race, such as typhoid fever (Fig. 23, F), 46 ELEMENTARY STUDIES IN BOTANY diphtheria '(Fig. 24, C), tuberculosis, and pneumonia, as well as some very destructive plant diseases, are caused by these bacteria. Other bacteria live in the soil, and are of enormous im- portance in changing the materials of the soil and in adding new material to the soil, making it possible for other plants to use the soil. The great importance of these bacteria to agriculture is coming to be recognized. 38. True Fungi. — The bodies of true Fungi consist of filaments, which may be interwoven more or less compactly. For example, the weav- ing may be so loose that the body is as delicate as a spider web, or it may be so close that the body is almost as compact as felt. This filamen- tous body is called a mycelium (Fig. 25). Molds. — The ordi- nary mold that ap- pears as a white furry growth on stale bread (when kept moist and warm) may be taken as an illustration (Fig. 25). The mycelium must be related to its food supply, and therefore it is observed spreading over the surface of the bread, evidently being a true saprophyte. Branches from the mycelium penetrate the bread, and into them the nutrient solution from the bread passes. These branches that receive the food supply are called hausloria (" suckers "), and of course are a very essential part of the vegetative body. Under suitable conditions, the prostrate mycelium also FIG. 26. — Section of a sporangium of Mucor developing, and show- ing how the partition wall is pushed up into the cavity of the sporangium. FIG. 27. — Section of a mature sporangium of Mucor, showing the spores. THALLOPHYTES 47 u;ives rise to erect branches, whose tips become sporangia that produce vast numbers of spores that are scattered by currents of air (Figs. 26 and 27). These spore-bearing branches are well called sporophores (" spore-bearers "). Under other conditions, two neighboring -mycelia form special branches that come together in pairs, tip to tip (Fig. 28). Each tip is cut off frpm the rest of the body by a wall, and the protoplasts of the two cells thus formed fuse, and a heavy-walled oospore is the result. This means thajt each tip-cell is a gametangium, and that the fusing protoplasts are gametes. The gametes and the gametangia usually look alike (Fig. 28, B) and behave alike, but it is found that the mycelia are sexually different. In some cases the gametangia differ in size (Fig. 28, C), so that a sexual difference is evident. Although one mycelium looks very much like another, the formation of oospores will not take place unless sexually different mycelia are brought together. For this reason the mycelium of molds may be grown indefinitely with- out producing oospores. The four things to observe, therefore, in the study of a true fungus, are the mycelium, the haustoria, the sporophores, and the sexual apparatus. A comparison of the mold with some other Fungi will illustrate how these four things vary. Downy mildews. — There is a group of Fungi called the " downy mildews/' which attack a great many plants, pro- ducing such diseases as potato rot, grape mildew, and com- Fio. 28. — Sexual reproduction of Mucor: A, the sexual branches in contact ; B, the two sex-organs (gametangia) cut off by walls ; C, the two pairing sexual branches and their gametangia unequal in size ; D, the oospore formed by the fusion of the protoplasts of the two gametangia. 48 ELEMENTARY STUDIES IN BOTANY mon diseases on many vegetables. In this group the my- celium lives upon a plant host and is a true parasite. It does not spread upon the surface of the host, but penetrates within it, crowding its way between the living cells of the host (Fig. 29) . Thus it is not only a parasite, but also an internal parasite. From its position against the living cells of the host, the myce- lium sends its haustoria through the cell-walls (Fig. 29), and into these haustoria the cell-sap of the proto- plast enters, so that the protoplast is dried out and dies. When a myce- lium is living in this way in the interior of a leaf, as a grape leaf, the drying out and killing of the leaf-cells by the haustoria is shown by the discolored and finally brownish spots that ap- pear on the leaves. FIG. 29. — Downy mildew : branch of mycelium in contact with two cells of a host plant, and send- ing into them branching haustoria. — After DE BARY. FIG. 30. — Downy mil- dew: sporophores emerging through the "breathing pores" of a leaf, branching, and bearing spores ; this form causes the potato rot. — After STRASBURGER. Then the mycelium sends its sporophores to the surface of the host (Fig. 30), for the spores must be formed where they can be scattered ; and it is the sporophores coming to the surface that represent the only part of trie parasite visible outside the host. These spores are not formed within spo- rangia, but are formed by cutting off the tip of the sporophore THALLOPHYTES 49 or the tips of its branches (Fig. 30). The sporophores reach the surface of the host either by emerging singly through numerous openings (" breathing pores ") in the epidermis C FIG. 31. — Downy mildew: A, oogonium (o) with antheridium (a) in contact; B, tube from antheridium penetrating oogonium ; C, oogonium containing the oospore. — After DEBARY. (Fig. 30), or by massing together and pushing up the epider- mis until it dries out and ruptures. In this latter case, the first appearance on the surface is a whitish blister. Later, the internal mycelium de- velops the sexual branches, which in this case are so different that they can be recognized as oogonia and an- theridia (Fig. 31). The antheridium sends out a tube that pierces the wall of the oogonium and through which the contents of the antheridium are discharged into the oogonium, in which the heavy-walled oospore is formed (Fig. 31). These sex-organs and the oospores are not brought to the surface of the host, as are the sporophores, for when the oospores are ready to germinate during the following spring, the host tissues in- closing them have decayed. FIG. 32. — Lilac leaf covered with mildew: the shaded regions representing the mycelium with its numer- ous spores (giving the dusty appearance) , and the black dots the spore- cases. 50 ELEMENTARY STUDIES IN BOTANY Powdery mildews. — There is another group of mildews (sometimes called " powdery mildews " to distinguish them from the " downy mildews ") that will illustrate the third relation of the mycelium to the food- supply. One of the most commonly observed among them is the lilac mildew. It is seen on every lilac bush as whitish, dusty-looking patches on the leaves (Fig. 32) ; in fact, whole bushes sometimes appear as if completely covered by street dust. Under the microscope it is seen that this whitish material on the leaves is the mycelium of a fungus, which in this case is an external parasite. The haustoria penetrate the walls of the epidermal cells of the host, which are really not vital cells, so that such mildews may be very abundant upon a plant without destroying it or seriously interfering with its vigor ; in fact, almost all plants have mildews. The mycelium produces sporo- phores abundantly, and it is really the numerous spores that give the dusty appearance to the leaves. These spores are formed as are those of the downy mildews de- scribed above, except that they are cut off in chains by an un- branched sporophore (Fig. 33). Later the sex-organs appear, very minute and not often seen, but the result of their work is always seen. This result is a heavy- walled case (Fig. 34), which FIG. 33. — A sporophore of a mildew with its row of spores. — After TULASNE. FIG. 34. — A spore-case of a mil- dew, showing its heavy wall, its conspicuous appendages, and the sacs (containing spores) squeezed out through a break in the wall. THALLOPHYTES 51 looks like a brownish or blackish dot on the lilac leaf (Fig. 32) . When this case is broken open, it is found to contain several thin- walled sacs (sometimes only one), within which are spores (Fig. 34). These heavy- walled cases, always bearing characteristic " appendages " (Fig. 34), are the protected structures that last through the winter, and it is their spores that start new mycelia during the following spring. How fertilization results in this case containing sacs with spores, is not necessary for the beginner to know. The three illustra- tions given show how the mycelium and the structures it produces are related to food- supply as saprophytes (as the molds) , external parasites (as the pow- dery mildews), or in- ternal parasites (as the downy mildews). The true Fungi are so very numerous that they cannot be pre- sented in a brief ac- count. It is impossible to give examples even of those that are of great economic importance ; but the above illus- trations will give some idea of the structure of the body and its relations to the food-supply, and two other illustrations are added because of their general interest. Wheat rust. — The rusts are destructive parasitic Fungi that attack very many plants, but public interest is chiefly directed to those that attack the great cereal crops, chief among which is wheat. The presence of rust in a wheat field is noticed first by the appearance of reddish, rusty- FIG. 35. — Summer spores of the wheat rust, which form the rusty lines on the wheat ; notice the two nuclei in each spore. FIG. 36. — Winter spores of the wheat rust; each spore has two cells, and each cell has two nuclei. 52 ELEMENTARY STUDIES IN BOTANY looking lines on the stem and leaves of some of the plants. These lines extend and multiply, new plants become in- fected, and presently the whole field may become rusty. A microscope shows that this rusty looking material is made up of spores (Fig. 35) ; and it is evident that they have been brought to the surface by sporophores arising from an internal mycelium. Later in the season, after the wheat has been harvested, there appear black lines on the stubble, the so-called " black rust." It does not belong to the stubble any more than to the rest of the plant, but it appears so late in the season that ordi- narily there is only stubble left to appear FIG. 37. — Winter spores of the wheat rust germinating, each filament con- sisting of four cells, and each cell send- ing out a delicate branch that pro- duces at its tip a spore (early spring spore). — After TULASNE. FIG. 38. — A cluster-cup (on barberry) of the wheat rust, containing rows of spring spores ; each spore contains two nuclei. upon. The " black rust " consists of heavy- walled spores that arise from the same mycelium (Fig. 36). There are thus two kinds of spores produced by the mycelium on the wheat ; one kind during the season, by means of which the rust is spread ; the other kind towards the end of the season. THALLOPHYTES 53 by means of which the rust is carried through the winter. Very naturally, the former are often called " summer spores" (Fig. 35), and the latter " winter spores" (Fig. 36). Early in the following spring the winter spores germinate, producing very short filaments, and these filaments put out a few slender branches, at the tip of each of which a spore is formed (Fig. 37). These little filaments that produce the third kind of spore are not parasites at all, for they are not related to any host. The spores they produce may be called the " early spring spores." The early spring spores ger- minate when they fall upon the right kind of host plant. In the wheat rust first studied in England, the host plant that received the early spring spores was found to be the barberry. The spores form an extensive internal mycelium in the bar- berry leaves, and this mycelium sends to the surface (usually the under surface) groups o— P. But when the fertilized egg of a liverwort germinates, it produces a very different kind of plant. This new kind of individual is a spore-case, which in most Liverworts has a stalk, and the FIG. 58. — Marchantia: an archegonium, showing the long neck, and the venter containing the egg. 76 ELEMENTARY STUDIES IN BOTANY stalk may be very long. This spore-case individual is usually without chloroplasts, so that it cannot manufacture food. It obtains food from the plant that produced the egg, usually by the end of its stalk becoming imbedded in the tissue of that plant. This imbedded part of the stalk often be- comes enlarged and is called the foot, and it is through the foot that food enters the spore-case individual, which is therefore a parasite. When the spores formed by this individual germinate, they do not produce other spore-case individuals, but they pro- duce the green liverwort body. The life-history of a liverwort, therefore, includes two in- dividuals that alternate with one another. One individual is green and bears the sex-organs (containing gametes), and hence is called the gametophyte (" gamete-plant ") ; the other is a parasite and produces spores, and hence is called the sporophyte (" spore-plant "). The fertilized egg of the game- tophyte produces the sporophyte, and the spore of the sporo- phyte in turn produces the gametophyte. The life-history formula, using G for gametophyte and S for sporophyte, thus becomes G=2>o — S — o — G=£> o — S, etc. This is alter- nation of generations, meaning that two individuals (gen- erations) alternate in the life-history. This is a most important fact in connection with Liverworts, because all of the higher plants continue this alternation, and their advance has depended upon the modification of these two generations. It must not be supposed that Liverworts introduced alternation of generations, for it was started among Algae, but Liverworts established it, and all plants afterwards retained it. It will be noticed that alternation of generations involves a division of labor. Among Algae that do not possess it, the same individual manufactures food, produces spores, and forms gametes. In Liverworts, the gametophyte manu- factures food and forms gametes, while the sporophyte BRYOPHYTES 77 produces spores. The gametophyte is the more conspicu- ous generation on account of food manufacture, which de- mands a display of green tissue, and therefore among Liver- worts the gametophyte is thought of usually as " the plant," and the sporophyte as its " fruit." Of course the sporo- phyte is in no sense a " fruit," for it has no more connection with the gametophyte than a parasite has with its host. Since gametophytes and sporophytes will be changing in appearance and relative prominence as we proceed through the higher groups, it is well to begin with a sure rule for recognizing them. Whatever a fertilized egg produces, no matter what it looks like, is a sporophyte ; and whatever a spore produces, no matter what it looks like, is a gameto- phyte. If this rule is remembered, the two generations will be recognized in spite of all their disguises. 47. The Mosses. — The Mosses are much more abundant now than the Liverworts, and are able to live in much more exposed places. In fact, Mosses are as- sociated with Lichens in the ability to live in conditions that are impossible for other plants. That ancient Liver- worts were the ancestors of Mosses is generally believed, and the first question is as to the differences that distinguish Mosses from Liverworts. It will be remembered that in some Liverworts the disk bearing the sex- organs is lifted up from the rest of the body by a long stalk (Figs. 53 and 54). Since this stalk bears the sex-organs (which contain the gametes), it is called a gametophore (" gamete-bearer"). In the Mosses this gametophore always appears, but instead of being a naked stalk, as in Liver- worts, it is covered with numerous small leaves (Fig. 59). FIG. 59. — The leafy gam- etophore (leafy branch) of a moss rising as a branch from the pros- trate filamentous body. 78 ELEMENTARY STUDIES IN BOTANY The distinguishing mark of a moss, therefore, is the leafy gametophore. It is these leafy and usually branch- ing gametophores that people in general think of as the " moss plant," for they are the most conspicuous part of it. It is evident that green tissue in the form of leaves on a gametophore is in a much better position in reference to air and sunlight than green tissue prostrate on some sub- FIG. 60. — The filamentous body of a young moss plant : A, the filament starting from the spore (s) ; B, the older filament, showing the branching habit, rhizoids (r), and a bud (6) which is to develop a leafy gametophore. — After MUELLER-THURGAU. stratum, as in the Liverworts. Since the leafy gameto- phore is only a vertical branch from the prostrate body, it is often called the leafy shoot. In most Mosses the prostrate (dorsiventral) body does not develop like those of Liverworts, but instead of being a flat sheet of cells, it is a green, branching filament, resem- bling a green, filamentous Alga (Fig. 60). It is important to know that when the liverwort body is developing it passes through a filamentous stage before it becomes a sheet of cells. This means that the filamentous body of the moss is not a BRYOPHYTES 79 different kind of body, but resembles a liverwort body that has not fully devel- oped. This failure of most Mosses to develop bodies to the mature liverwort stage is probably associ- ated with the fact that the gametophore bears leaves and the chief work of food manufacture is done no longer by the pros- trate body. The picture of a moss, therefore, is a delicate, prostrate, branching, green filament (which most peo- ple do not see), from which arise numerous vertical leafy branches (which most people regard as the whole plant), and since these leafy branches are gametophores, they bear the sex-organs. There is some excuse for regarding the branching gameto- phore as the whole plant, for it sends out its own rhizoids into the substratum, the delicate green filament from which it arose dies, and the gametophore becomes com- pletely independent (Fig. 61). In addition to this, the gametophore can repro- duce extensively by vegetative multiplication, so that masses and " beds " of moss are formed. In fact, most FIG. 61. — A, a leafy branch (gametophore) that has become independent by putting out its own rhizoids ; B, a rosette of leaves surrounding a group of sex-organs (forming the so-called "moss flower"). FIG. 62. — Tips of leafy branches of a moss, one of them bearing a group of sex-organs surrounded by a rosette of modified 'leaves. 80 ELEMENTARY STUDIES IN BOTANY of our experience with Mosses is their occurrence in sheets and beds. 48. The sex-organs. — It is evident that the prostrate filamentous body of a moss with its leafy gametophore branch is the gametophyte generation. The antheridia and arche- C FIG. 63. — Sex-organs of a moss: A, an antheridium discharging sperms, one of which is shown (c) ; B, section of a group of archegonia invested by leaves : C, an arche- gonium, with its long neck, and its venter containing an egg. — After SACHS. gonia have the same general structure as do those of Liver- worts (Fig. 63), and are borne in clusters at the tips of branches or of the main axis (Fig. 62). The leaves about these ter- minal clusters often become close set, forming a rosette, and they may differ in appearance (size or color) from the other BRYOPHYTES 81 leaves (Figs. 61, B, and 62). These rosettes of leaves in- closing sex-organs have been called moss " flowers/' but they hold no relation to real flowers. In a single one of these moss rosettes both kinds of sex-organs (antheridia and arche- gonia) may occur, or only one kind (Fig. 63, B). In the latter case, therefore, there are male rosettes and female rosettes ; and if such rosettes occur on different plants, there are male plants and female plants. 49. The sporophyte. — The sporophyte of a moss is much more elaborate than that of a liverwort. Usually it is long- stalked, the capsule (spore-case) opens by a lid, the spore-bearing region is small compared with the rest of the sporophyte, and the whole structure is very complex (Figs. 64 and 65) ; but it still lives as a parasite on the gametophyte, and is com- monly (and wrongly) called the " fruit" of the moss. 50. Evolution of the sporophyte. - After the establishment of alternation of generations by Liverworts, the most im- portant fact in connection with Bryo- phytes (Liverworts and Mosses) is the progress made by the sporophyte, which is usually spoken of as its " evolution." It was upon the sporophyte that the whole future of the plant kingdom de- pended, for it is the structure of the sporophyte that de- termines the higher groups. First stage of the sporophyte. — The simplest sporophytes among the Liverworts are merely spore-cases, consisting of a jacket of sterile cells (cells that do not produce spores) FIG. 64. — Two moss plants (leafy gam- etophytes) bearing mature and long- stalked sporophytes ; the spore-case on the left is still covered by the cap (calyptra) formed by the arche- gonium; the spore- case on the right shows the lid which drops off and ex- poses the spores. 82 ELEMENTARY STUDIES IN BOTANY investing a mass of spore-producing cells (Fig. 66, A). There is no stalk, and there are no sterile cells except the single layer forming the jacket. When the sporophyte gets to be very complex, it is important to remember that the oldest tissue in it (historically) is that which produces spores (sporogenous tissue), for this will clear up many false im- pressions. Progressive changes. — The conspicuous change observed in certain other Liverworts is that the cells inclosed by the sterile jacket do not all produce spores. For example, in some forms one-half of the inclosed tissue pro- duces spores and the other half remains sterile (Fig. 66, B). This sterile tissue forms a short stalk, and so different regions of the body begin. In other forms, still more tissue remains ster- ile, which means that the sporogenous tissue be- comes relatively less in amount (Fig. 66, C). With the increase of sterile tissue, the stalk and the capsule become more complex (Fig. 66, D) ; until in the higher Mosses almost the whole complex sporo- phyte is sterile, and the sporogenous tissue is not only relatively small in amount, but appears late in the develop- ment of the sporophyte (Fig. 66, E). The sporogenous tissue which in the beginning was the first and only tissue (except the sterile jacket), becomes finally in the higher Bryophytes the latest and most inconspicuous part of the sporophyte. ' It is the ever increasing sterile tissue that the higher plants use in carrying the sporophyte to still more advanced stages. FIG. 65. — Spore-cases of a moss from which the lids have fallen, showing the teeth. — After KERNER. BRYOPHYTES 83 Anthoceros. — Among the Liverworts there is a group of which Anthoceros may be used as a representative. The body is a prostrate sheet of cells, some- times lobed but not leafy, and resembles the bodies of many Liverworts (Fig. 67). It is not complex either in structure or in form, but it has a remark- able sporophyte. It is believed by many that this represents the kind of liverwort spo- rophyte that gave rise B FIG. 66. — Diagrams illustrating the evolution of the sporophyte among Bryophytes: A, sporo- phyte of Riccia, being only a spore-case ; B, sporophyte of Marchantia, showing a reduced amount of sporogenous tissue, and the sterile cells forming a short stalk; C, sporophyte of a leafy Liverwort, showing further reduction of sporogenous tissue and corresponding increase of sterile (stalk-forming) tissue ; D, sporophyte of Anthoceros, showing further decrease of spo- rogenous tissue and increasing complexity of capsule and stalk (including foot) ; E, sporo- phyte of a Moss, showing extreme reduction of sporogenous tissue and great complexity of cap- sule and stalk; the numerals (1-1) indicate the first wall of the dividing egg (note that in A and B the two halves of the egg contribute almost equally to the sporophyte ; that in C one-half of the egg produces the sporophyte ; that in D the first wall is vertical ; and that in E almost all the sporophyte is produced by one-half of the egg. FIG. 67. — Anthoceros: the pros- trate body bearing long and narrow sporophytes ; the two sporophytes to the left are mature and have split to discharge the spores. to the higher groups of plants. If this is true, such a sporophyte deserves special attention. Throughout the Bryophytes (Liverworts and Mosses), 84 ELEMENTARY STUDIES IN BOTANY the sporophyte is dependent upon the gametophyte, and is never an independent plant. In the higher groups (Fern- plants and Seed-plants) the sporophyte is an independent leafy plant. In some way, the dependent, leafless sporophyte of Bryophytes becomes the independent, leafy sporophyte of Pteridophytes (Fern-plants), and the liver- wort Anthoceros has a sporophyte that has suggested the way. Just as Liver- worts are more important than Mosses in the history of the plant kingdom, so are the Anthoceros forms the most im- portant Liverworts in the history, al- though they are the least abundant. From what has been said, it is evident that any sporophyte of the Bryophytes that shows a tendency to become inde- pendent is on the way towards an inde- pendent sporophyte, and when complete independence is attained the sporophyte no longer belongs to Bryophytes. The peculiarity of the Anthoceros sporophyte is that it is more nearly independent than the sporophyte of any other bryophyte. This sporophyte does not consist of a roundish spore-case on a more or less elongated stalk, as in other Liverworts and in the Mosses, but elongates without a stalk, until it resembles a small grass- blade (Fig. 67). The most striking fact, however, is not its form, but that it is as green as a grass-blade. The presence of chloroplasts means that this sporophyte is able to manu- facture food, and although it has a bulbous foot sunk in the thin body of the gametophyte (Fig. 68), it does not FIG. 68. — Anthoceros: longitudinal section through the sporo- phyte (broken into three regions), show- ing the bulbous foot imbedded in the gametophyte, and the three regions of the sporophyte above : (1) the green region (four layers of cells), (2) the spore-producing re- gion (the stages in spore-formation may be observed by trac- ing this region from below upwards), and (3) a central region. BRYOPHYTES 85 obtain all its food from the gametophyte. If such a sporo- phyte should establish connections with the soil (on which the gametophyte is lying) by means of roots, it would be- come an independent plant, and no longer be a bryophyte. Although the sporophyte of Anthoceros has been likened to a small grass-blade in form and color, it is very far from having the structure of a grass-blade, for it is in no sense a leaf. It is a stem-like structure, which has the power of elongating like a stem, and a section across it shows three regions (Figs. 68 and 69) ; (1) a green region on the outside, (2) a spore- producing region next to the green, and (3) a central region of colorless and sterile cells. This is the structure which is thought to have given rise to sporo- phytes with stems and leaves. 51. The failure of Bryophytes. — This J r J FIG. 69. — Anthoceros: does not mean that Bryophytes are cross-section of a spo- ,, ., • ,i i f '. i rophyte, showing the failures in themselves, for it has been three regions de- seen that they are abundant enough to esf t'he very distSt be called successful. The failure referred sur[ace l?y*T °f ce«« is the epidermis. to is that the bryophyte plan could not make any further progress leading to higher plants. We infer that this is true, simply because the plan of the higher plants is different. A gametophore is developed by many Liverworts and by all Mosses. As the name implies, this stalk carries up the gametes (eggs and sperms) above the general surface of the prostrate body. Since the fertilized egg produces the spo- rophyte with its spore-case, the gametophore certainly puts the spores in a favorable position for dispersal by air. If this position favors the spores, however, it does not favor the sperms which must swim, for they are carried up into a position of least moisture. It is an interesting arrangement that favors spores by interfering with the very act (fertiliza- 7 86 ELEMENTARY STUDIES IN BOTANY tion) that results in spores ; but it works reasonably well for plants living in moist situations. The Mosses use the upright gametophore for the display of green tissue, and it becomes leafy ; but the larger and more exposed the gametophores of Mosses become, the more un- likely it is that fertilization can occur. It is evident that still larger and more leafy plants would interfere with the swimming of sperms still more. The three things that enter into this problem are food manufacture (which means display of green tissue to light and air), fertilization (which means water for swimming), and spore-production (which means exposure for air-disper- sal). • In the Bryophytes, food manufacture and fertilization belong to the gametophyte, and the condition that favors one hinders the other. In other words, they are contradic- tory in their demands. On the other hand, food manufac- ture and spore-dispersal make the same demands for exposure, and therefore they can be coupled together to advantage. The further progress of plants, therefore, demanded that the spore-producing generation (sporophyte) should also become the food-manufacturing generation; and that the gameto- phyte, with its peculiar need for free water, should be re- stricted to fertilization. In the higher plants (Fern-plants and Seed-plants), therefore, the sporophyte is the conspicuous, leafy, independent generation, and the gametophyte is so very inconspicuous that it is only seen by those who know where and how to look. 52. Summary. — The contribution of the Bryophytes to the progress of the plant kingdom is notable. Of first importance is the establishment of the land habit by green plants (Liverworts), which means exposure to air rather than to water7~7This made possible the further development of plants on the land surface. In consequence of this change in conditions of living, the plant bodies are much more com- pact, and develop protective structures against excessive BRYOPHYTES 87 loss of water by evaporation. Not only are the working bodies protected, but the sexual-cells are jacketed, so that the sex-organs (antheridium and archegonium) are many- celled. ^ The most significant result of the land habit was the es- tablishment of an alternation of generations, so that sporo- phyte and gametophyte alternate regularly in the life-history. Among Bryophytes the gametophyte is the conspicuous generation, because it manufactures food in addition to pro- ducing sex-organs, and the sporophyte is dependent upon it. In one group of Bryophytes (Anthoceros) the sporophyte is green, so that the possibility of an independent sporophyte is evident. The further progress of the plant kingdom is dependent upon an independent sporophyte, because the free display of green tissue by a gametophyte means conditions unfavorable for the swimming of sperms necessary to fertilization, while the free display of green tissue by a sporophyte means con- ditions favorable also for the dispersal of spores. CHAPTER VI PTERIDOPHYTES THE FIRST VASCULAR PLANTS 53. Recapitulation. — The history of the plant kingdom has been followed from the Algae, exposed to water, to the Liverworts, exposed to air. From the Algse the dependent Fungi seem to have come, and together the two groups con- stitute the Thallophytes, the lowest great division of plants. From the Algse the Liverworts also came by acquiring the land habit, and in turn gave rise to Mosses, and Liverworts and Mosses together constitute the Bryophytes, the second great division of plants. In the Bryophytes the body is more complex than in the Thallophytes, is related to air exposure, and alternation of generations is established. In this alter- nation the gametophyte is the independent generation, dis- playing the green tissue and bearing the sex-organs ; and the sporophyte is a dependent generation. In such Liverworts as Anthoceros, however, the dependent sporophyte has ad- vanced far towards independence, as shown by its develop- ment of abundant green tissue, which makes the sporophyte only partially dependent. Therefore, it seems probable that the Liverworts gave rise not only to the Mosses, but also to the third great division of plants (Pteridophytes), with its completely independent sporophyte. It is important, there- fore, to examine the structure of the independent sporophyte, for it involves much more than the appearance of green tissue. 88 PTERIDOPHYTES 89 54. The vascular system. — In all independent sporo- phytes there develops a tissue which does not appear in the dependent sporophytes of Bryophytes. It is called vascular tissue, which means a tissue composed of vessels. The so-called vessels are thick-walled, tubular cells that extend through the sporophyte and are equipped to conduct water. The vascular tissue does more than conduct water, but its other work will be considered later. Of course water is conducted through the bodies of Liverworts and Mosses, but the vascular tissue conducts it with more rapidity and precision than any other tissue. The difference between water-conduction in a liverwort and in a plant with vascular tissue may be likened to the difference between water work- ing its way through a swamp and water moving in definite channels. It must not be supposed that the water-conducting vessels are continuously open tubes, as are the arteries and veins of the human body or the water pipes of a house. They are elongated cells set end to end, so that water in moving through the tissue must pass through numerous cell-walls, thousands of them in an ordinary stem. How water moves under these conditions is not known with certainty, but the direction of its movement is clear. The vascular tissue does not extend at random through the body of the sporophyte, but has a definite organization, so that there is a vascular system in every sporophyte. The vascular system has proved to be of very great service in the study of the relationships of vascular plants, for it differs in the various great groups. That part of the vascular tissue which conducts water is called the xylem, which means. " wood," for the ordinary wood of trees is xylem tissue. 55. The leaf. — In addition to a vascular system, the independent sporophyte has leaves. Leaves are simply ex- pansions of green tissue that increase the amount of green tissue exposed, and so increase the capacity of the plant for 90 ELEMENTARY STUDIES IN BOTANY food-manufacture. It must not be supposed that leaves do all the work of food-manufacture, for it is done by any green part of the plant ; but leaves do the most of it because they display the most green tissue. The leaves of leafy Liverworts and of Mosses have been spoken of, but those leaves belong to the gametophyte. It FIG. 70. — Portion of the leaf of a maidenhair fern (Adiantum), showing the forking veins. • is in vascular plants that one meets the first sporophyte leaves ; and they are very different in structure from gameto- phyte leaves. An important fact to observe in connection with the leaves of vascular plants is that they are not merely expansions of green tissue, but that through the green tissue there extend " veins " (Fig. 70). These so-called veins are extensions of the vascular system into the leaf, for the xylem carries water PTERIDOPHYTES 91 to the working cells. Leaves differ in the arrangement of their veins, but every arrangement means an effective dis- tribution of water to the working cells. There are main veins (often only one) that give rise to smaller ones, and these in turn to still smaller ones, until the system of veins forms a complete network through the green tissue (Fig. 155). The system may be likened to the water-pipe system of a house, with its main pipe, which gives off smaller pipes, and these in turn still smaller ones, until every room in a large house may be supplied with water. / The vein system of / a leaf, in addition to / carrying water, inci- dentally forms a stiff framework with its woody fibers, which helps to support the I delicate green tissue and keep it from col- lapsing. It is known to every one that leaves are ex- tremely variable in size and form. For exam- ple, among the Pteridophytes, the first great group of vas- cular plants, they are very small in the Club-mosses (Fig. 71), and are often very large among the Ferns (Fig. 72). Also in the Club-mosses the whole leaf is a single small blade FIG. 71. — Branch of a club-moss (Selaginella,), showing the numerous simple leaves; the leaves at the tips of the branches bear spo- rangia, and therefore are sporophylls, so that each branch-tip in this case is a strobilus. 92 ELEMENTARY STUDIES IN BOTANY (as the green expansion is called), while in many Ferns the large leaf may be broken up into many blades (Figs. 70 and 72). Since the largest amount of working tissue is exposed to the air by leaves, it follows that the leaves lose most water. (FIG. 72. — Shield ferns (Aspidium), showing the large leaves broken into many blades. They must be kept full of water and they must be exposed to the air, so that great loss is inevitable, and the vascular system must make it good. The escape of water from plants, chiefly by way of the leaves, is called transpiration, but it might just as well be called plant-evaporation, for the water evaporates from the moist cells of the plant just as it does from any moist surface exposed to the air. How the leaves PTERIDOPHYTES 93 are constructed so that the loss of water may not be greater than the supply will be considered later. 56. The stem. — An independent sporophyte has not only a vascular system and leaves, but also a stem ; in fact, the presence of leaves implies a stem to bear them. The most important fact about a stem is that it bears leaves and exposes them to the air and the sunlight. In proportion as stems be- come taller, the better are the leaves exposed ; and in propor- FIG. 73. — Cross-section of the central cylinder of the stem (rootstock) of a fern ; the cylinder is solid, the large water-conducting vessels (xylem) being at the center. tion as the stems become branched, more leaves can be pro- duced and exposed. As the stems carry the leaves up into the air and sunlight, they must also supply them with water, and this means that the vascular system of the stem must connect with the vas- cular system (vein system) of the leaves. In the stem the vascular system is organized as a central cylindei^so that it is called the vascular cylinder (Figs. 73 anoT74)7 This cyl- inder not only conducts water, but also gives rigidity to the 94 ELEMENTARY STUDIES IN BOTANY stem, so that in most cases it stands upright. The move-^ ment of water up the stem, through the vascular cylinder, is commonly spoken of as the " ascent of sap," the " sap being water on its way to the leaves. It must not be supposed that all stems are upright, for in many Olub-mosses they are prostrate, but as they elongate they produce and display many leaves. Nor must it be sup- posed that all stems are above ground, for in the most common Ferns the stem is underground, but it sends its leaves above ground. These under- ground stems are usually mistaken for roots, but they can always be recog- nized as stems by the/ fact that they produce/ leaves and by the kind of vascular cylinder they possess. 57. The root. --An independent sporophyte has not only a vascular system, leaves, and a stem, but also roots. The leaves need water, which the stem supplies, but roots must receive water from the soil and supply it to the stem. Thus, the vascular system is a water-conducting system connecting the roots with the leaves, through the stem. No one of the four structures mentioned as belonging to an independent sporophyte is independent of the others. The presence of leaves implies a vascular system, a stem, arid a root ; and so for each structure in turn. They all belong together as parts of one machine. How the roots receive water from the soil will be considered later. FIG. 74. — Cross-section of the central cylinder of the stem of a fern ; the water-conduct- ing vessels form a hollow cylinder inclosing pith. PTERIDOPHYTES 95 Roots not only receive water, but they also anchor the I plant in the soil, so that the grip of the roots and the rigidity ' of the stem hold the plant firmly in place. FIG. 75. — A club-moss (Lycopodium) : A, the whole plant, showing the horizontal and very leafy stem giving rise to roots and erect branches bearing very distinct strobili (composed of sporophylls) ; B, a single sporophyll with its sporangium ; C, spores much magnified. — After WOSSIDLO. The root differs very much from the stem in structure, and especially is it different in its vascular cylinder, and in the 96 ELEMENTARY STUDIES IN BOTANY fact that it does not produce leaves. Like the stem, it often branches, and this means a greater capacity for receiving water. It must not be supposed that all roots are in the soil, for some roots are produced in the air by climbing stems, and anchor the stems to supports. In this case they simply act as holdfasts and do not receive water, but they can be recog- FIG. 76. — Under surface of fern leaves, showing sori : A, elongated sori ; B, round sori. nized as roots by the vascular cylinder and by the fact that they do not bear leaves. 58. The sporangia. — A sporophyte, whether dependent or independent, must bear spores, and these spores must be placed in a favorable position for dispersal by air. In the dependent sporophyte of Bryophytes, the conspicuous part PTERIDOPHYTES 97 of the body is a spore-case, and all the spores are produced in one continuous mass. In the independent sporophyte of Pteridophytes, however, the root, stem, and leaves are the conspicuous structures; and if the spores are to be formed in the most exposed position it is evident that they should appear in connection with the leaves. Therefore, among Pteridophytes the spore-cases (sporangia) are produced by FIG. 77. — Section through a sorus of a shield fern, showing the group of sporangia covered by a shield-like (or umbrella-like) flap. — After ENQLER and PRANTL. leaves, in some plants by all the leaves, in other plants only by certain leaves. In the Club-mosses, with their small leaves, a single spo- rangium is produced on the upper surfaco of the leaf near its base (Fig. 75). In some of the Club-mosses every leaf has a sporangium ; but in most of them only the uppermost leaves have sporangia (Fig. 75). In the latter case, there are two kinds of leaves on the plant ; (l) those that bear sporangia, and (2) those that do not. The former are called sporophylls (" spore-leaves ")> and the latter foliage leaves (which means ordinary green leaves). 98 ELEMENTARY STUDIES IN BOTANY In the Ferns, with their relatively few and large leaves, the sporangia are borne in large numbers on the under surface of the leaf, and usually occur in small groups that look like dark dots or lines (Fig. 76), which are often called " fruit-dots," but of course they are not fruit. In some Ferns al- most all of the leaves bear sporangia, while in other Ferns many leaves are without them. These little groups of sporangia are called sori (singular sorus), and they are very characteristic of Ferns. A section through a sorus is shown in Fig. 77. 59. The gametophyte. — The sporophyte, with its root, stem, leaves, and spo- rangia, seems to most people to be the whole plant. A fern plant, as ordinarily thought of, is simply this sporophyte, and it is certainly a dis- tinct and independent individual. But it bears no sex-organs ; if it did, it would not be a sporophyte. The older observers of plants were puzzled by the absence of sex-organs in Ferns and Club-mosses, but they thought that sex-organs must be present, although invisible. Therefore, they called the group Cryptogams, which means " hidden sex-organs," and since Club-mosses and Ferns are vascular plants, the Pterido- phytes were first called " Vascular Cryptogams," and many FIG. 78. — Gametophytes of ferns: A, a game- tophyte viewed from the under side (against the substratum), showing the rhizoids and sex-organs, the archegonia (whose projecting necks are seen) being grouped near the notch , and the antheridia being grouped at the other end (in the region of the most con- spicuous rhizoids) ; B, a gametophyte (under surface) from one of whose fertilized eggs (within an archegonium) a young sporo- phyt* is developing, the root being directed downward and the leaf rising upward through the notch. FIG. 79. — Section of an archegonium of a fern, showing the free neck, and the imbedded venter containing the egg (the large cell). PTERIDOPHYTES 99 still use that name, although the sex-organs have been found. The alternation of generations explains what was a mystery to the older botanists. When the spore of a fern germinates, it must produce a gametophyte (see § 46, p. 77) . This gameto- phyte is a minute green plant that looks like a very small and delicate liverwort (Fig. 78, A). In fact, it is so small that it is only seen by those who know where to look for it ; and FIG. 80. — Antheridia of a fern : A, two antheridia, one containing sperms and the other discharging them ; B, a single sperm, showing its coiled form and many cilia. it does not suggest a fern in the least. Although it is flat and prostrate like a liverwort, unlike a liverwort it produces the sex-organs (antheridia and archegonia) from the under surface, against the moist substratum (Figs. 79 and 80). This position is very favorable for the swimming of sperms, for if there is moisture anywhere about the plant, it will be found between the flat body and its substratum. The necks of the archegonia also open on the under surface, so that fertilization is favored in every way. The small gametophyte is large enough to produce sex- organs, and it does not make food for the sporophyte, so that 100 ELEMENTARY STUDIES IN BOTANY great exposure to drying out is avoided, and fertilization is assured. When the fertilized egg in the archegonium germinates, it produces the large, independent sporo- phyte which is recog- nized as " the fern " (Fig. 78, B). It may have been difficult for some to think of the spore- case of a liverwort or a moss as being an individual distinct from the green plant that bears it ; but when in the Ferns these two individuals become entirely in- dependent of one an- other, the difficulty disappears. 60. The great groups of Pterido- phytes.— The Pteri- dophytes are very an- FIG. 81. — Equisetum: showing the jointed and fluted cient plants for their stem, the sheath of minute leaves at each joint, strobili in various stages of development, and history has been some young branches. -, -, -, ,-, traced back to the time when coal was formed, and even before that time. Their remains are found in the rocks, and this record of their existence has shown not only that they were very abundant, but . also that they were different from the Pteridophytes that are living to-day. A number of great groups lived and flourished and then disappeared, but they PTERlDOtfHYTES 101 produced descendants, and among these descendants are the Pteridophytes of the present time. The history and fate of these ancient groups may be likened to the history and fate of such old empires as those of Egypt, Greece, and Rome, which lived and flourished and then disappeared, but they also gave rise to descend- ants, and among these descendants are various nations of the present time. There are three promi- nent groups of Pterido- phytes living to-day, and they are common enough to deserve recognition. (1) Club-mosses (Ly- copodiales) . — These plants, resembling coarse mosses, are recognized by their numerous small leaves (Figs. 71 and 75), and by the fact that the sporangium-bearing leaves (sporophylls) bear a single sporangium upon the upper surface near the base. They are sometimes called "ground pines," because the coarser ones resemble seedling pines in general appear- ance. Among the ancestors of the present Lycopodiales there were large trees, so that during the Coal Age the 8 FIG. 82. — A branching Equisetum. 102 EH^ARY STUDIES IN BOTANY Lycopodiales were conspicuous members of the forests. At present, however, they are all small and mostly prostrate plants that send up vertical branches bearing the sporangia. (2) Horsetails (Equisetales). — These plants are sometimes called " scouring rushes," and are so peculiar in appearance that they can never be mistaken. The stems are green and jointed, and often the joints can be pulled apart easily (Fig. 81). At each joint there is a circle of minute leaves forming PIG. 83. — Young fern leaves arising from the subterranean stem (rootstock), and show- ing the rolled tip. a toothed sheath, but they are not foliage leaves, for they do not display green tissue. As a consequence, the stem looks bare, which is especially noticeable when it does not branch. When branching occurs, it may be very profuse, so that the plant looks like a miniature bush (Fig. 82). Since there are no foliage leaves, all the work of food manufacture must be •done by the green tissue of the stem. The Equisetums (which seems to be a better name to use 103 104 ELEMENTARY STUDIES IN BOTANY than horsetails) also have forest trees among their ancestors of the Coal Age, and the appearance of these conspicuously jointed trees would have been very peculiar to one familiar only with trees of the present day. Many of the ancient representatives of the group had foliage leaves, and in some cases large ones, so that the living Equisetums are rather poor representatives of the group. (3) Ferns (Filicales) . — These are the most abundant and best known of the Pteridophytes, and hardly need a definition. Compared with Club-mosses, Ferns have large and relatively few leaves, which bear numerous sporangia upon the under surface. Not only are the leaves large, but sometimes they become very large by branching. It is not by its form that a fern leaf can be distinguished from other leaves, but by its forking veins (Fig. 70), and by the fact that it first appears as if rolled up from the tip to the base, and then it expands by unrolling (Fig. 83). The leaves of Ferns were once called " fronds," because they were thought to be different from leaves. It was observed that they came di- rectly from the ground, arising from an underground struc- ture that was thought to be a root (Fig. 83) . Therefore, the leaf-like structure was thought to be a combination of stem and leaf, to which the name " frond " was given. Of course a fern leaf is not a frond, as the underground structure re- ferred to is a stem and not a root, but many still call it a frond. The Ferns of ordinary experience are tufts of leaves arising from an underground stem (Fig. 72), which also sends out roots ; but there are many tree Ferns in the tropics, the un- branching trunk (often tall and slender) bearing a crown of large and branching leaves (Fig. 84) ; and there are climbing Ferns in our own eastern mountain region; and numerous perching Ferns occur in the tropics, often covering the trunks and branches of trees (Figs. 85 and 86). 61. The strobilus. — This word means " cone," and its use here refers to the fact that in some Pteridophytes the FIG. 85. — Perching ferns (with hanging leaves) on a tree in Mexico. — Photograph by LAND. 105 105 ELEMENTARY STUDIES IN BOTANY FIG. 86. — A large staghorn fern perching on a tree in Australia. — Photograph by CHAMBERLAIN. sporophylls (see § 58, p. 97) become different in appearance from the foliage leaves (usually smaller, and often different in form), and are grouped close together in the form of a cyl- inder or cone (as in the pine cone). This group or cone of PTERIDOPHYTES 107 sporophylls is the strobilus (Figs. 75 and 81), and it is a very important structure, for it is the precursor of the flower. In general, the Club-mosses have strobili very distinct from the rest of the body (Fig. 75), for they are borne at the ends of the vertical branches, and are often stalked far above the foliage-bearing part of the stems. It is these strobili that are the " clubs" of the Club-mosses, a name which may now be interpreted as meaning moss-like plants that bear clubs. It must be kept in mind that in these strobili of Club-mosses, each sporophyll bears a single large sporangium on its upper surface near the base, and that a strobilus is simply the tip of a stem (or branch) bearing sporophylls so close together that they overlap. The Equisetums also have strobili (Fig. FIG. 87. — Equisetum: A, a single sporophyll, showing the peltate top from which the sporangia hang; B and C, spores showing the unwinding of the peculiar bands that form the outer coat. FIG. 88.— Ophio- glossum (adder's tongue) : a fern with a part of the leaf bearing sporangia. 81), and the sporophylls are very different from those of the Club-mosses, for each sporophyll is a stalk-like structure with an expanded top (" peltate "), from the under side of which several sporangia are suspended (Fig. 87). The Ferns do not have strobili, although in some of them there are sporophylls distinct from foliage leaves, and in more 108 ELEMENTARY STUDIES IN BOTANY of them certain branches of the leaf bear sporangia and differ very much in appearance from the foliage branches (Fig. 88). But in no case are sporophylls grouped together to form strobili. 62. Heterospory. - In most of the Pterido- phytes, all the spores produced by the spo- rangia are alike, both in appearance and in the gametophytes they pro- duce. This condition is called homospory (" simi- lar spores "), and such plants are homosporous. In some Pterido- phytes, however, notably one kind of club-moss (Selaginella, Fig. 71), the spores are not all alike (Fig. 89). They differ very much in size, the large ones being called FIG. 89. — Selaginella (a club-moss) : A, a spo- t megdSpOreS (" large rophyll (microsporophyll) bearing the spo- rangium (microsporangium) that produces small spores (microspores) ; B, microspores (lowest one separate, upper ones clinging together) ; C, a sporophyll (megasporophyll) bearing the sporangium (megasporangium) that produces large spores (megaspores) ; D, two megaspores, drawn to the same scale as the microspores (B). spores ") and the small ones microspores ("small spores"). Not only do they differ in size, but they differ also in the gametophytes they pro- duce, the megaspores producing female gametophytes (that is, gametophytes that bear only archegonia), and the microspores producing male gametophytes (that is, gameto- phytes that bear only antheridia). This condition is called PTERIDOPHYTES 109 heterospory (" different spores "), and such plants are heterosporous. Heterospory is extremely important, for it is the condition that leads to seed-formation ; that is, heterospory is the pre- cursor of the seed. Pteridophytes in general are not heter- osporous, but heterospory began among Pteridophytes, and when it reached the formation of seeds, then Seed-plants (Spermatophytes) began. Not only are the spores of heterosporous plants different, but the two kinds are produced by different sporangia (Fig. 89). Therefore the sporangia that produce megaspores are called megasporangia, and those that produce microspores are called microsporangia. In Selaginella (the heterosporous Club-mosses) the megasporangia are usually in the lower part of the strobilus, and the microsporangia in the upper part. The difference in the size of the spores involves a difference in the number of spores produced by the two kinds of sporangia. In Selaginella, for example, a megasporan- gium usually contains four megaspores, while a microspo- rangium contains hundreds of microspores. Since the two kinds of sporangia are approximately of the same size, this difference in the number of spores will give some idea of their difference in size (Fig. 89). It is necessary also to recognize the fact that the sporo- phylls that produce the two kinds of sporangia may become different ; in fact, among the Seed-plants they become very different. In order to distinguish them, the sporophylls producing megasporangia are called megasporophylls ; while those producing microsporangia are called microsporophylls. A little experience with these terms will make them recall easily the structures they stand for, especially if their rela- tions are remembered as follows : a megasporophyll bears one or more megasporangia, which contain megaspores; and when megaspores germinate, they produce female gameto- phytes, that is, gametophytes that bear only archegonia 110 ELEMENTARY STUDIES IN BOTANY (which contain the eggs) ; a microsporophyll bears one or more microsporangia, which contain microspores ; and when microspores germinate, they produce male gametophytes, that is, gametophytes that bear only antheridia (which contain the sperms). It may help to remember what heterospory involves in the life-history of a plant by giving the formula of the life-history of a heterosporous plant, which of course must include two gametophytes. The sexual cells (egg and sperm) are indi- cated by the conventional sex signs ( ? is for female, and $ for male), and the two kinds of spores are indicated by their relative size. G-9 x ,*>- G— 3. Gametophytes. — In § 59 (p. 98) the gametophyte of a fernN^vas described, which may stand in a general way for the gametophytes of most Pteridophytes, for most Pteridophytes are homosporous. These gametophytes are alike in usually bearing both sex-organs, therefore they are not male or female, but both ; and also they are quite independent of the sporo- phyte which produced them by means of its spores. But in heterosporous plants there are two kinds of game- tophytes, and these must be described if one is to understand seeds when they appear. When a microspore germinates, there appears within it a small group of cells, but the group never grows so as to PTERIDOPHYTES 111 break through the wall of the microspore and develop a free plant (Fig. 90). When it is remembered that whatever a microspore produces must be a male gametophyte, no matter what it looks like, this small group of cells within the micro- spore must be the male gametophyte. When the group is examined, it is discovered that there is a single antheridium, with its wall in- closing sperm- producing cells. This represents a gametophyte that FIG. 90. — Selaginella: the male gametophyte completely developed within themicrospore ; the group of squarish cells with nuclei are those that produce sperms. — After Miss LYON. FIG. 91. — Selaginella: the female gametophyte within the megaspore, but having burst through on one side : m, megaspore wall ; a, archegonium ; r, rhizoid. has disappeared from ordinary sight, and that can be discovered only by the microscope. When a megaspore germinates, there appears within it a much larger group of cells than appears in the microspore (Fig. 91), for the megaspore is much larger than the micro- spore. But even this larger group of cells does not free itself from the megaspore wall and grow into a free plant ; but it does develop archegonia, and must be the female gameto- phyte. In heterosporous plants, therefore, the two gametophytes 112 ELEMENTARY STUDIES IN BOTANY have disappeared from ordinary sight, and it is not sur- prising that the large and conspicuous sporophyte is thought to be the whole of the plant; it is certainly the whole of the plant in sight. To find the gametophytes, one must look within the microspores and megaspores with a micro- scope. It is instructive to trace the history of the gametophyte and sporophyte generations through the great groups of plants. In Bryophytes, the gametophyte is the conspicu- ous individual, the sporophyte being dependent upon it and being not much more than a spore-case. In the Pterido- phytes, the sporophyte has become the conspicuous individual, but in most Pterido- Bryophytes Pteridophytes Spermatophytes FIG. 92. — Diagram illustrating the advance of the sporophyte and the decline of the gametophyte through Bryophytes, Pteridophytes, and Sperma- tophytes. phytes the phyte is a free and independent individ- ual, although rela- tively very small. In the heterosporous Pteridophytes and in all the Seed-plants, the gametophytes are neither free nor independent, and have disappeared from view within the spores that produce them. The accom- panying diagram (Fig. 92) will illustrate the gradual advance of the sporophyte and the gradual decline of the gametophyte through the plant kingdom. 64. Summary. — The most, important fact in connection with the Pteridophytes is the appearance of an independent sporophyte, which is now the conspicuous generation. With the appearance of an independent sporophyte there are asso- ciated three structures not found in the lower groups of plants : the vascular system, the sporophyte leaves, and the root. A second important fact is that among the Pteridophytes the strobilus appears, which is the precursor of the flower. PTERIDOPHYTES 113 The strobilus is not a feature of all Pteridophytes, not appear- ing among the Ferns, but it is a structure begun by the group. A third important fact is the appearance of heterospory, for this is the precursor of the seed. This means a differentia- tion of the spores into two kinds, one kind (the smaller ones) producing the male gametophytes, the other kind (the larger ones) producing the female gametophytes. Another accom- paniment of heterospory is that the gametophytes are de- pendent and so small that they remain within the spores that produce them. CHAPTER VII SPERMATOPHYTES. — 1. GYMNOSPERMS THE FIRST SEED-PLANTS 65. The great plant groups. — In beginning a study of the fourth great group of plants, it is appropriate to fix in mind the chief distinguishing features of all the groups. The following statement of contrasts may serve this purpose. Thallophytes. — Plants with a thallus body, but no arche- gonia. Bryophytes. — Plants with archegonia, but no vascular system. Pteridophytes. — Plants with a vascular system, but no seeds. Spermatophytes. — Plants with seeds. Each of the definitions (except the last) contains a positive and a negative statement, the positive statement distinguish- ing the group from the one below it in rank (except the first), and the negative statement distinguishing the group from the one above it in rank. The four great groups should not only be kept clearly in mind by brief definitions, such as those given above, but they should also be remembered for their chief contributions to the progress of the plant kingdom. The most conspicuous contributions may be stated as follows. Thallophytes. — This group, as represented by the Algae, stands for the beginnings of plant structures, and chiefly for the evolution of the three kinds of reproduction. Bryophytes. — This group, as represented by the Liver- worts, stands for acquiring the land habit (which means air 114 SPERMATOPHYTES 115 as a medium), and for establishing the alternation of genera- tions. Pteridophytes. — This group stands for the development of the vascular system (with its associated leaves and roots), for the introduction of the strobilus, and for the beginning of heterospory. Spermatophytes. — This group stands for the development of the seed and for the evolution of the flower. 66. The two great groups of Seed-plants. — The Seed- plants are the most conspicuous plants to-day, for they make up nearly all the vegetation that one sees. They are cer- tainly more important than the other groups, not only in prominence and in numbers, but also in the use made of them. They are so prominent and useful that they were once thought to be the only group worth studying ; but it is known now that Seed-plants can be understood best by allowing the other groups to explain them. The Seed-plants have developed as two great groups : (1) those in which the seeds are exposed, and (2) those in which the seeds are inclosed. The first group is named Gymno- sperms (" naked seeds"), and the second is named Angio- sperms (" inclosed se*eds "). The Gymnosperms are the ancient Seed-plants, and are now much less numerous than the more modern Angiosperms. It is the Gymnosperms, therefore, that developed the first seeds and that must be considered first. 67. The ancient Gymnosperms. — In most ancient times in which we have plant records, when the coal was being formed, and there were tree Club-mosses and tree Equise- tums, the oldest Gymnosperms lived. They were very abundant, for their leaves are found everywhere in the rocks about the coal mines. The leaves resemble those of Ferns .so exactly that they were thought to belong to Ferns, but recently it was discovered that they bore seeds, and therefore they are Gymnosperms. The first Seed-plants, therefore, 116 ELEMENTARY STUDIES IN BOTANY looked like Ferns bearing seeds, and it is believed that they came from very ancient Ferns by acquiring the seed habit. These fern-like Gymnosperms gave rise to other groups, and these in turn to still others, until finally the Gymno- sperms of to-day appeared. 68. The modern Gymnosperms. — The greatest group of modern Gymnosperms is the one to which pines, spruces, FIG. 93. — A group of Conifers (mostly spruces) along the southern boundary of the White River Forest Reserve, Colorado. — Photograph by LAND. hemlocks, cedars, etc., belong (Fig. 93), and is called Conifers (" cone-bearers ") on account of the cones the plants (usually trees) bear. These Conifers are found in forest masses, sometimes very extensive, throughout the north temperate regions, and they extend farther south along the mountain ranges. Many of them are extremely valuable for timber, and it is well known how extensively and ruthlessly they have been destroyed by man. In the temperate regions of the southern hemisphere there is also a great display of Conifers that differ from those of the northern hemisphere. SPERMATOPHYTES 117 Scattered through the broad tropical belt between the two temperate regions there is another group of modern FIG. 94. — A Mexican Cycad (Dioon edule). — Photograph by CHAMBERLAIN. Gymnosperms, called Cycads. They resemble tree ferns, with their columnar trunks bearing crowns of large fern-like 118 ELEMENTARY STUDIES IN BOTANY leaves (Fig. 94). Sometimes the trunks are short, resem- bling casks or large tubers, but they always bear the crown of fern-like leaves. There are two other living groups, very much scattered, and very few in numbers, so that they need not be described. The pine will be used as a representative of Gymnosperms, since it is a conspicuous and familiar form. 69. The sporophyte. — The pine " tree " is of course a sporophyte that has become very large (Fig. 93). The vascular cylinder of the stem is thick, and it becomes thicker each year by adding new layers of wood. This continual increase in the amount of water-conducting tissue makes wide and continued branching possible, for branching means an increase in leaf display, and increased leaf display means a larger supply of water not only for food manufacture, but chiefly to supply the loss from the leaves. The tree type of body, with its tall trunk and spreading branches bearing a great mass of foliage, is the most advanced type of sporophyte body. In other words, it is the sporophyte at its best. In the pine the leaves are not broad, being only green •" needles," but they are very numerous (Fig. 95). There are Conifers, however, with broad leaves, and the Cycads have very large fern-like leaves (Fig. 94). 70. The strobili. — A pine tree bears two kinds of strobili (" cones "), but many Gymnosperms have the two kinds of strobili on different trees. The pine cone that is ordinarily seen is the strobilus that bears megasporangia ; that is, it is a group of megasporophylls. It is so much larger and more persistent than the other kind that to most people it seems to be the only kind of cone on the tree. But there are also small strobili composed of groups of microsporophylls bear- ing microsporangia (Fig. 95). Ovulate strobilus. — If one of the larger cones of the pine is cut through lengthwise (Fig. 96, A), it will be found to SPERMATOPHYTES 119 consist of a central axis bearing numerous close-set mega- sporophylls, which are very firm, and finally become very hard. On the upper side of each megasporophyll near the , a FIG. 95. — Tip of a pine branch, showing ovulate cones of first year (a), second year (6), and third year (c) ; also a cluster of staminate cones (d). base are two megasporangia, lying side by side (Fig. 96, B and C). The megasporophylls lie so close together that the megasporangia cannot be seen from the outside, but when the 120 ELEMENTARY STUDIES IN BOTANY strobilus matures, the hard megasporophylls spread apart and the megasporangia become exposed. These structures of Seed-plants were known long before the corresponding structures of the lower groups, and of course they received names. It is necessary now to fit the two sets of names to- gether, so as to recog- nize what the old names really stand for. The megasporophylls of Seed-plants were called carpels, long before they were known to represent structures belonging to Pteridophytes. Ap- proaching them from the Pteridophytes, we find that the so-called carpel of Seed-plants is a megasporophyll, and this is an illustration of what was meant when it was stated that a lower group of plants explains a higher one. The megasporangia of Seed-plants were called ovules (the structures that become seeds), and thus we learn that the ovules of Seed-plants are megasporangia. This is im- portant, because ovule means " a little egg," and the thought was that the ovule is an egg. The previous chapters have made it plain that an egg and a sporangium are about as different as two structures can be; not only that, but that the egg belongs to the gametophyte, and the sporangium to the sporophyte. The word " ovule" is not likely to be dis- FIG. 96. — Ovulate cone of pine : A , cone partly sectioned, showing the central axis and the overlapping carpels ("scales") bearing ovules (megasporangia) near the base ; B and C, single carpels, showing the pair of ovules borne on the upper side. SPERMATOPHYTES 121 carded, although its real meaning records a mistake, for it has been long used and is shorter than megasporangium. In using it, however, it must be realized that " ovule " is just another name for the megasporangium of Seed-plants. It is convenient to have a name to distinguish the stro- bilus that bears ovules (megasporangia) from the one that does not, and the most appropri- ate one seems to be ovulate strobilus or ovu- late cone. Some persist in calling the ovulate cone the " female cone " ; but the cone (strobilus) is made up of sporo- phylls borne by a spo- rophyte, so that it can- not very well be either male or female, terms FIG. 97. — Staminate cone of pine : A, longi- that belong tO the ga- tudinal section of cone, showing the stamens mo+rmUxH-o (microsporophylls) bearing pollen sacs (mi- tupliy l/e. crosporangia) upon the under side ; B, views Staminate strobilus. — of stamen from the side and from below> the latter showing the two pollen sacs; C, The Smaller COne Of the cross-section of a stamen, showing the two • n i £ i pollen sacs containing pollen grains (micro- pine Will DC IOUnd tO spores) ; D, a winged pollen grain, showing consist of microsporo- ™^n the early cells of the male gameto" phylls borne upon a cen- tral axis, much smaller and more delicate than the megasporo- phylls (Fig. 97, A). On the under side of each microsporo- phyll are two microsporangia, lying side by side (Fig. 97, B and C). The old names for these structures among Seed- plants are as follows : the microsporophylls were called stamens, the microsporangia were called pollen sacs, and the microspores were called pollen grains or simply pollen. In this way it has become evident that such well-known struct- 122 ELEMENTARY STUDIES IN BOTANY ures among Seed-plants as stamens, pollen sacs, and pollen grains, correspond to the microsporophylls, microsporangia, and microspores of the Pteridophytes. Since stamen is so much more convenient a term than microsporophyll, the cone which bears microspo- rangia (pollen sacs) may be called the staminate strobilus or staminate cone, but it should be realized that " stamen " is only another name for the microsporophyll of Seed- plants. It is the stami- nate cone that is often called a " male cone," which is no more appro- priate than to call the ovulate cone a " female cone." Also, there is no objection to calling the microspores " pollen," provided it is remembered that " pollen " is only another name for the mi- crospores of Seed-plants. 71. The ovule. — It is the ovule (megasporan- gium) that distinguishes Seed-plants, for it devel- ops into the seed, and therefore it must differ somewhat from the megasporangia of Pteridophytes. If it is cut through lengthwise, its general structure will be evident (Fig. 98, A). On the outside of it there is a covering which is loose above and extends into a A B PIG. 98. — A, section of scale of ovulate cone, showing the bract beneath (6), the scale (s), the ovule (o), with its integument and nucellus, and within the nucellus the mega- spore (0) which probably contains the be- ginning of the female gametophyte ; B, a section through the ovule a year later, showing the large female gametophyte (g) with two archegonia (a) which are being reached by pollen tubes (t) penetrating the tip of the nucellus; observe also the in- tegument at the top of the ovule with its passage way (micropyle) to the nucellus. SPERMATOPHYTES 123 more or less extended tube. The covering is the integument, and the tube is the micropyle (" little gate "). Within the covering is the body of the ovule (nucellus), with its tip at the base of the open micropyle. If the ovule is a mega- sporangium, it must contain megaspores, and these are found in the nucellus. Several megaspores start, but only one grows, and it becomes so large that it looks like a cavity in the middle of the nucellus (Fig. 98, A). The peculiarity of this megasporangium (the ovule) is not that it has only one megaspore, or that the megaspore is so large, but that it is never shed, that is, it never escapes from its megasporangium. The fact that this megaspore is retained in its sporangium is- the reason why the ovule becomes a seed. 72. The stamen. — There is nothing peculiar about the stamen (microsporophyll), except that among Gymnosperms it becomes more and more unlike a leaf in appearance. In some Cycads it appears as a flat blade bearing sporangia (pollen sacs) on its under surface ; in pines the blade becomes short-stalked (Fig. 97, B) ; and in many other Gymnosperms the stalk becomes elongated and the blade reduced to a plate or knob bearing the pollen sacs. When two regions of a stamen are distinguishable as a stalk region and a pollen-sac region, the former is called the filament, and the latter the anther. These names are often convenient in describing stamens, but they only mean that some microsporophylls have stalks distinct from the sporangium-bearing region. 73. The gametophytes. — In the preceding chapter (§ 63, p. 110) it was stated that the gametophytes of heterosporous Pteridophytes do not emerge from the spores that produce them. Of course all Seed-plants are heterosporous, and, therefore, just as in heterosporous Pteridophytes, the male gametophyte develops within the microspore (pollen grain), and the female gametophyte develops within the megaspore which is retained within the megasporangium (ovule). This means that in Seed-plants the gametophytes are in- 124 ELEMENTARY STUDIES IN BOTANY visible to the ordinary observer, for they are living, like in- ternal parasites, within structures of the sporophyte. The female gametophyte. — The large,, solitary megaspore within the ovule develops within itself the female gameto- phyte, which consists of numerous cells (Fig. 98, B). Cells on the side of the gametophyte towards the tip of the nucel- lus, which means also towards the micropyle, develop archegonia (Fig. 98, B), and in each archegonium, of course, there is an egg. It becomes evident now that an " ovule " is very far from being an egg, although it received its name be- cause it was thought to be an egg. It is helpful in fixing the relations of parts to remember that the egg is in an archego- nium, the archegonium is produced by the gametophyte, the gametophyte is within the megaspore, and the megaspore is within the ovule (megasporangium) . Of course the egg is passive and remains in the archegonium, awaiting fertiliza- tion. The male gametophyte. — The microspores (pollen grains) do not remain within the microsporangia (pollen sacs), but are discharged and are widely scattered by the wind. When the pollen of pines is being shed, the air is sometimes full of the small " grains " (spores), which look like yellow powder, and they settle down like rain. In the pines, the pollen grains have wings (Fig. 97, Z>), but this is not true of all Conifers. Of course very few pollen grains land on the right spots, but there are so many of them that some reach the proper landing places. The " right spots " are the ovulate cones, whose hard megasporophylls (carpels), often called the " scales " of the cone, have spread apart to receive them. The minute pollen grains slip down the sloping scale and col- lect in a little drift at the bottom, around the projecting micropyle. Then some of them get into the micropyle and reach the tip of the nucellus, which is their destination. This transfer of pollen from the pollen sacs (microsporangia) to the ovulate cone, and in the cone to the tip of the nucellus, SPERMATOPHYTES 125 FIG. 99. — Two views of the sperm of a Cycad, showing its spiral form and many cilia. is called pollination, and in the Gymnosperms the agent of this transfer is the wind. Such plants, therefore, are said to be wind-pollinated. Before the pollen grains (microspores) leave the pollen sacs, the male gametophyte has begun to develop within them (Fig. 97, D), and after the pollen has reached the nucellus, the gametophyte con- tinues to develop, form- ing an antheridium, which in almost every Gymnosperm produces two sperms. In the Cycads these sperms have cilia and swim (Fig. 99), just as do those of the Pteridophytes ; but in the Conifers the sperms have no cilia, and of course do not swim. 74. Fertilization. — After pollination has been accom- plished, and the pollen grain (microspore) of the pine, with its contained male gametophyte, is resting on the tip of the nucellus, the sperms and the eggs are separated from one another by the mass of tissue that forms the top of the nucel- lus. This tissue must be penetrated, and the pollen grain (really the male gametophyte within it) puts out a tube (pollen tube) which grows into it, crowding its way among the cells, absorbing nourishment from them like an internal parasite, and finally reaches the egg (Fig. 98, B). In the tip of the advancing tube the two sperms are tying, and when the vicinity of the egg is reached, they are discharged from the tube, and one of them penetrates the egg and the two nuclei fuse. The result, of course, is a fertilized egg lying deep in the ovule. Pollination and fertilization should not be confused, as they often are. When pollen is carried to an ovulate cone 126 ELEMENTARY STUDIES IN BOTANY of a pine (or to a flower in higher plants) it is often called " fertilization/' but it is evident that it is not. Pollination is a performance that must precede fertilization, and it may or may not be followed by fertilization, which is the fusion of a sperm and an egg. 75. The embryo. — The fertilized egg, lying within the ovule, begins to germinate almost at once, and as the young sporophyte (embryo) grows, it feeds upon the surrounding cells of the female gametophyte, and finally reaches a stage in which the different parts become distinguish- able (Fig. 100, A). In the pine, the three re- gions are a stem-like part (hypocotyl) whose tip is directed towards the top of the nucellus (which means that it is directed towards the micropyle) J a rosette of leaf-like parts (cotyledons) ; and in the midst of the rosette of cotyledons, and resting on the top of the hypocotyl, a minute bud-like part (plumule). The hypocotyl will later develop the root, the plumule will develop the stem and leaves, and the cotyledons will for a short time supply nourishment to the young plant. Although the fertilized egg germinates almost at once, and the embryo grows until the three regions described appear, it does not continue to grow without interruption, but passes into what is called the dormant (" sleeping ") stage, and the dormant embryo is one of the peculiarities of Seed-plants. FIG. 100. — A, section of a pine seed, showing the hard coat (testa), the female gameto- phyte (dotted) which has grown to the testa and is usually called endosperm, and the embryo (also sectioned) with its hypocotyl, its cotyledons (three only are shown), and the plumule (the short protuberance) sur- rounded by the cotyledons ; B and C, ger- mination of the pine seed, the cotyledons backing out of the testa in B and entirely free in C. SPERMATOPHYTES 127 Just what conditions result in dormancy we do not know in all cases, but we do know some facts that are associated with it. What these are will be described in the next section. 76. The seed. — While the embryo is being formed, changes are taking place in the integument of the ovule. A new kind of tissue begins to develop from the cells of the integument, and continues to develop until it forms a hard covering that completely invests the ovule, the only breaks in it being at the micropyle (whose position is indicated by what looks like a small scar) and at the point where the ovule (megasporangium) was attached to the carpel (mega- sporophyll). When this hard coat (testa) is complete, the ovule has become a seed (Fig. 100, A). It is evident that the seed is a very complex structure, and that it has resulted from the retention of the megaspore within the megasporangium (ovule), so that within this sporangium the female gametophyte develops, fertilization takes place, and the young sporophyte (embryo) is formed. In a seed, therefore, three generations are represented : (1) the old sporophyte, represented by the ovule structures ; (2) the female gametophyte, very commonly called the en- dosperm of seeds ; and (3) the young sporophyte (embryo) . It is a simple thing to observe the structure of a seed and to watch its " germination," but really to know the structure of a seed needs the approach to it from the lower groups of plants. A seed is said to " germinate," but it is plain that it is not germination in the sense we have been using that word, for only spores and fertilized eggs (oospores) germinate. Besides, germination occurs when the fertilized egg within the ovule produces the embryo; therefore, when a seed is said to " germinate," the real germination had occurred long before, usually the preceding season, sometimes many seasons before. What " seed germination " means, therefore, is not real germination, but the " awakening " of the young 128 ELEMENTARY STUDIES IN BOTANY sporophyte (embryo) from its dormant condition, and the resumption of its growth, and its escape from the seed coat (Fig. 100, B and C). Of course seeds will always be said to " germinate," for the word is too firmly established in this connection to be changed, but the student of botany should realize that " seed-germination " is not the starting of a new individual (which is real germination), but the continued growth of an individual that has been started already. The resumed growth of the embryo, and its escape as a " seed- ling," will be considered in connection with the other great group of Seed-plants, whose seeds are those most frequently " germinated " by those who cultivate plants. 77. Summary. — The Gymnosperms are the most ancient Seed-plants, continuing and advancing the structures of the Ferns, from which they differ chiefly in the presence of seeds. The vascular system is notably developed, resulting in larger sporophyte bodies, and in a greater display of foliage. The earliest Gymnosperms did not have strobili, resembling the Ferns in this feature, but all other Gymnosperms have strobili as a very conspicuous feature. The important fact about Gymnosperms, however, is the existence of seeds. A seed is derived from an ovule, and an ovule is a megasporangium. The difference between an ovule and any other megasporangium is that the ovule retains its megaspores instead of shedding them. This re- tention of the megaspore means that the female gameto- phyte develops within the ovule, that fertilization occurs there, and that the embryo sporophyte develops there. When all of these structures within the ovule become in- cased by a hard coat (testa), the total structure is the seed. The transportation of pollen (pollination) is effected by the wind, and after fertilization the embryo develops three regions (hypocotyl, cotyledons, and plumule) and then passes into a dormant stage. Activity is resumed when the conditions for " seed-germination " are present. CHAPTER VIII SPERMATOPHYTES. — 2. ANGIOSPERMS THE REAL FLOWERING PLANTS 78. General character. — The Angiosperms have several superlative features. They are the most advanced, the most recent, the most conspicuous, and the most useful of plants. The vegetation that covers the earth is in the main angio- sperm vegetation, and when to this is added the fact that the Angiosperms are almost the only plants that men use, it is not strange that they were once thought to be the only plants worth studying. Perhaps the best reason for study- ing the lower groups is that Angiosperms may be understood better. Some more definite appreciation of the relative abundance of Angiosperms may be obtained from the state- ment that about 450 different kinds (species) of living Gymnosperms are known, while about 130,000 different kinds of Angiosperms have been recorded. In the preceding chapter (§ 66) it was stated that An- giosperms differ from Gymnosperms in having the seeds inclosed. The inclosing structure is the carpel, which thus forms a " seed-vessel " of extremely variable appearance. Using the terms applied to these structures in the lower groups, the statement would be that the megasporophyll incloses the megasporangia (ovules) . It must not be thought that the inclosure of the ovules is the only character that distinguishes Angiosperms from Gymnosperms. It is so obvious a feature that it suggested the name of the group, but there are many other important differences. 129 130 ELEMENTARY STUDIES IN BOTANY 79. The sporophyte. --The habit of the sporophyte, as its general appearance is called, shows every possible variation, as would be expected in so large a group. One of the oldest groupings of plants recognized this fact in classifying them as herbs, shrubs, and trees. Of course these names are retained for general use, but they cannot be denned with exactness. The sporophyte is extremely variable not only in habit, but also in structure. In general, the structure of the stems and leaves is quite different from that found among Gymno- sperms, almost every trace of the ancient fern connection having disappeared. The root, stem, and leaf are such important organs that they deserve separate treatment, and this has been deferred until the greatest display of these organs has been reached in the Angiosperms. Their place in the history of the plant kingdom has been stated, but it remains to consider their work, especially as such knowledge is essential to any intelligent cultivation of plants. This subject will be treated in subsequent chapters. 80. The flower. — The most characteristic structure of Angiosperms is the flower. This does not mean that all Angiosperms have flowers, but that Angiosperms have de- veloped the flower. In § 61 (p. 107) it was stated that the strobilus is the precursor of the flower. Throughout Gym- nosperms the strobilus is the nearest approach to the flower, and among the simpler Angiosperms the strobilus continues. It is necessary to have clearly in mind the distinction between a strobilus and a flower. It is a distinction of con- venience and riot of exactness, for the two structures grade insensibly into one another. A strobilus is a group of sporo- phylls, organized together so as to form a structure distinct from the foliage-bearing part of the plant. A strobilus- bearing plant, therefore, has two kinds of lateral members : sporophylls. and leaves. A flower introduces a thirdJateral member, the perianth, which is associated with the sporo- SPERMATOPHYTES 131 phylls. A flower, therefore, may be said to be a strobilus with a perianth. Originally a flower was thought to be essentially a group of sex-organs, and therefore a sexual structure. It is evident that it consists of members (peri- anth and sporophylls) borne by a sporophyte, and there- fore it cannot be a sexual structure. It is impossible to apply the term strobilus and flower strictly among Angio- sperms, for some flowers have no perianth because they have never had one, and therefore are strobili; and others have no perianth because they have lost it, and there- fore are flowers by de- scent. Among Angio- sperms, therefore, it is convenient to speak of all sporophyll-bearing -^ j / structures as flowers. 81. The perianth. /FlG 101 _ Flower of peony: &, sepals (forming J It is evident that the \ the calyx); c> Petals (forming the corolla); calyx and corolla^ together constiiuig the perir perianth IS the distin- j "SS&Z a, starnenTf O, carpels (oT^istils). — After . , . i r , STRASBURGER. guishing mark of a \ flower; in fact, it is just the mark that people in general use in recognizing a flower. One of the features of Angio- sperms is the endless variation in the structure of the perianth, so that the different kinds of flowers become the most valuable means of classifying Angiosperms. The term perianth is a collective one, to include all the members ; but it is used chiefly in cases where the members are all approximately alike, as in the lilies and their allies. \ In most Angiosperms, however, the perianth is differentiated into two sets, calyx and corolla (Fig. 101). The calyx, whose individual members are called sepals, is the outer \set and usually green in color; while the corolla, whose 132 ELEMENTARY STUDIES IN BOTANY individual members are called petals, is variously and usually brightly colored, forming the showy part of the flower. In fact, it is the corolla that usually gives character and at- traction to the flower. These general statements in reference to the calyx and corolla must not be applied too rigidly. For example, the calyx may be brightly colored and showy, FIG. 102. — Flower of tobacco : A, sympetalous corolla ; B, tube of corolla cut open and showing stamens ; C, the pistil (carpels), showing ovary and style (the stigma forms the surface of the knob-like tip of the style). — After STRASBURGER. the corolla may not be showy or even colored, both sets may be showy, neither set may be showy or colored, etc. The general roles played by calyx and corolla have to do with the sporophylls. The calyx protects the young and growing parts within while the flower is in bud. The showy corolla is related in some way to the visits of certain insects (as bees, butterflies, moths, etc.), which become agents in transporting pollen (pollination , see § 73, p. 125). This sub- SPERMATOPHYTES 133 iect of the relation of insects to flowers is a very large one, and will be presented in the following chapter. The great variation in the structure of the corolla is the variation of chief service in classification, so far as the peri- anth is concerned. A great many terms have been applied to the different conditions of the corolla, and a few of the most significant conditions are as follows. The simplest kind of corolla is one in which the petals are free from one another and are all alike. Such a corolla is said to be poly- petalous (of " many petals ") and regular. In many flowers B E FIG. 103. — Sympetalous flowers: A, bluebell; B, phlox; C, deadnettle; D, snap- dragon ; E, toadflax ; C,' D, E are irregular flowers (bilabiate in this case) . — After GRAY. the petals appear as if united to form tubes, bells, funnels, etc. (Figs. 102 and 103), and such a corolla is said to be sympetalous (" petals together "). This sympetalous con- dition is so constant in families of plants, that the highest one of the three great groups of Angiosperms is named the Sympetalce, because in all of its families the flowers are sympetalous. In certain families the petals of a flower are not all alike ; and then the corolla is said to be irregular. For example, the sweet pea and its allies have very irregular flowers, the petals being very much unlike, but the corolla is polypetalous. In the snapdragon, which is sympetalous, the rim of the tube has the appearance of two unequal lips, 10 134 ELEMENTARY STUDIES IN BOTANY three of the petals entering into the structure of the upper lip, and the other two petals forming the lower lip (Fig. 103, C, D, E). Such a corolla is naturally called bilabiate (" two- lipped "), and a large family of the Sympetalae is called the Labiatce (" lipped ") because its flowers have this two-lipped structure. These are simply conspicuous illustrations of irregular corollas. 82. The stamen. — It was among the Angiosperms that the name stamen was given long ago to the sporophyll that bears microsporangia, and since it was recognized to be necessary to seed-forma- tion, it was thought to be the male organ, and the pollen grains (microspores) it produced were thought to be male cells. FlGof\^e^mr°st«Sr Jt is eyident tnat sporophylls and mi- showing filament and crospores belong to the sporophyte, a anther, the latter ap- , . ,. . , , sexless individual, so that the stamen cannot be a male organ. The mistake which the sac splits to discharge the pol- len. — After SCHIM- PEB. chiefly as two pollen sacs ; the ver- tical line shown in the left pollen sac of was natural, because the minute gameto- the left stamen in- dicates the line along phytes had not been discovered. The stamens of Angiosperms vary ex- tremely in appearance, but in most cases two distinct regions can be recognized (Fig. 104). There is a stalk-like region, which is long or short, slender or broad, called the filament, and a terminal region that bears the microsporangia, called the anther. The filament puts the anther in a favorable position for dis- charging its pollen grains, which are to be carried away by the wind or by insects or by some other agency. The anther consists of the top of the sporophyll and usually four microsporangia, two on each side (Fig. 105). As the microsporangia grow, the two on each side usually run to- gether and become one cavity (Fig. 106), so that in the mature anther there are usually two sacs (Fig. 104) containing pollen SPERMATOPHYTES 135 grains (microspores). It is these sacs, usually consisting of two fused microsporangia, that are called pollen-sacs in FIG. 105. — Cross-section of a very young anther of a lily, showing the four developing sporangia. Angiosperms. A pollen-sac opens to discharge the pollen, usually by splitting down the line where the two microspo- FIG. 106. — Cross-section of a mature anther of a lily (much larger than that shown in Fig. 105), showing the two chambers formed by the four sporangia, and also the region of opening for each chamber (s). 136 ELEMENTARY STUDIES IN BOTANY rangia come together (Fig. 104), but sometimes there is formed an opening (pore) at the top, which may even be extended into a tube (Fig. 107). The stamens, like the petals and sepals, are not always free from one another, for sometimes the filaments appear as if they had been united. In some plants, for example, FIG. 107. — Anthers opening by terminal pores: A, potato or tomato; B, arbutus; C, cranberry or huckleberry. — A and B after ENGLER and PRANTL, C after KEENER. the stamens appear united in this way in two or more sets, and sometimes they. form a single set, all of the filaments together forming a tube (Fig. 108). In sympetalous corol- las it is usual for the stamens to appear as if arising from the tube of the corolla (Fig. 102, £). This means that the petal set and stamen set have developed together, so that they are not distinct from one another at base. While the two kinds of sporophylls (stamens and carpels) are usually associated in the same flower, there are many SPERMATOPHYTES 137 Angiosperms whose flowers contain only one kind of sporo- phyll. This means that such plants have two kinds of flowers, one containing stamens, and the other containing carpels. These two kinds of flowers may be produced by the same plant or by different plants. In the latter case, there are two kinds of sporophytes, differing in their flowers, one kind bearing staminate flowers (with stamens only), and the other kind bearing car- pellate flowers (with car- pels only). For example, FIG. 108. — Section of a flower of Althaea, showing sepals (a), petals (6), tube of stamens (c) inclosing the style (d), and also the ovules (e) within the ovary. — After BERG and SCHMIDT. FIG. 109. — Indian corn (maize) : A, showing the "tassel" (made up of staminate flowers) ; B, showing the ear (made up of carpellate flowers) within its husk and the exposed "silk" (made up of the long, protruding styles). — After DEVRIES. the corn plant has the two kinds of flowers, but both are borne by the same individual (sporophyte), the staminate flowers forming the " tassel " and the carpellate flowers the " ear " (Fig. 109) ; while in the chestnut, one tree bears staminate flowers (and therefore does not produce chestnuts) and another tree bears the carpellate flowers. 83. The carpel. — It has been stated that the term " carpel" has been applied among Seed-plants to the structure called 138 ELEMENTARY STUDIES IN BOTANY megasporophyll among Pteridophytes ; tnat is, the carpel is a megasporophyll. It has been stated also that the angio- sperm carpel differs from that of the Gymnosperms in in- closing the megasporangia (ovules), the number inclosed ranging from one to very many. In forming a case about the ovules, two regions of the car- pel usually become evident (Figs. 102, C, and 110) : (1) a more or less bulbous region that incloses the ovules (the ovary), and (2) a more or less extended beak-like re- gion arising from the ovary (the style) . The name ovary was given ^vvhen the ovules were thought to be eggs, and both names are unfortunate, for they imply what is not true, but they have been used for so long a time that it would be more confusing to replace them than to retain them. The significance of the style is found in the fact that it provides a special re- ceptive surface (the stigma) for the pollen grains, and the length and form of the style are answers to the problem of the most favorable position for the stigma. Very commonly the style swells into a knob at the top, and the surface of this knob is the stigmatic surface (Figs. 102, C, and 110, C). Sometimes the stigmatic surface extends down the side of a style, as in corn, in which the so-called " silk " is made up of styles (Figs. 109, and 110, B). Rarely, there is no style at all, and the stigmatic surface is upon the ovary itself. It is evident, therefore, that the two essential features of an FIG. 110. — A, simple pistils (each one a single carpel) ; B and C, compound pistils (each one composed of several carpels) ; in B the stigma extends along the sides of the styles, in C it is on the terminal knob of the style. — After BERG and SCHMIDT. SPERMATOPHYTES 139 angiosperm carpel are the ovary and the stigmatic surface, and that a style is generally present because it insures a more favorable position to the stigmatic surface for receiving the pollen. A flower may have a single carpel, or it may have several. In the latter case, the carpels are arranged in one of two ways : (1) they may be distinct from one another (Fig. 110, A), or (2) they may be organized together in a single body (Fig. 110, B and C). It is convenient to have a term that may be applied to either situation, and that term is pistil. FIG. 111. — Cross-sections of ovaries of compound pistils : A, three carpels forming a "one-celled" ovary; B, three carpels forming a "three-celled" ovary.. — After SCHIMPEB. A pistil is a single structure, with its ovary, style, and stig- matic surface, but it may consist of a single carpel or of two or more carpels organized together. These two conditions of the pistil are distinguished as simple pistils and compound pistils (often called syncarpous pistils, which means pistils with " carpels joined together "). The term pistil, there- fore, is one of convenience rather than of exactness, for sometimes it is identical with carpel and sometimes it in- cludes two or more carpels. It is like the word " house, " which may include one room or two or more rooms. It fol- lows that there are three possible carpel conditions in a flower : (1) a solitary carpel and therefore a single pistil ; (2) two or more carpels forming as many pistils; and (3) two or more carpels forming a single pistil. 140 ELEMENTARY STUDIES IN BOTANY In the compound (syncarpous) pistil there are two dif- ferent conditions of the ovary that must be mentioned. In the one case, the carpels are arranged so as to inclose a single cavity, as if open carpels had united edge to edge (Fig. Ill, A). In the other case, the carpels are arranged so that there are as many cavities as there are carpels, as if closed carpels had come together, each with its own cavity (Fig. Ill, B). These cavities within the ovary were long ago called " cells," and the inappropriateness of the term is evident. Therefore, some ovaries are said to be one-celled FIG. 112. — Sections of ovules, showing outer (oi) and inner (ii) integuments, micro- pyle (m), nucellus (n), and megaspore (em) ; in B the ovule is curved, and in C the stalk is curved, so that in both cases the micropyle h turned towards the wall of the ovary. and some are two- or more-celled. It must be noticed that this does not correspond necessarily to the number of carpels, for although a simple pistil has a one-celled ovary, a com- pound (syncarpous) pistil may have either a one-celled ovary or a several-celled ovary. 84. The ovule. — The structure of the angiosperm ovule is essentially the same as that of the gymnosperm ovule. That is, there are one or two integuments investing the nu- cellus, whose tip is exposed at the micropyle (Fig. 112). In the midst of the nucellus the usually solitary megaspore appears, for, as in Gymnosperms, although several . mega- spores start, it is seldom that more than one develops to the full size and power. SPERMATOPHYTES 141 The position of the ovule within the ovary cavity has certain features that must be noted. The ordinary entrance to the nucellus is through the micropyle, and therefore the position of the micropyle is important. In some cases, the ovule arises from the bottom of the ovary cavity (or near it) and grows directly away from the wall of the ovary, so that the micropyle is as far from the wall as it can be (Fig. 112, A), which is a relatively unfavorable position. In most Angio- sperms, however, the ovule or its little stalk (funiculus) curves in growing, so that the micropyle is brought relatively near the wall of the ovary (Fig. 112, B and C). That this position is a favorable one is evident when it is understood that the pollen tube grows along the wall of the ovary and enters the ovule by way of the micropyle. In examining ovules it will be found that most of them are not straight, but are curved in various ways, and the curving means a more favorable relation of the micropyle to the entrance of the pollen tube. 85. The gametophytes. — It was stated (§ 73, p. 123) that among the Gymnosperms the male gametophyte is represented by a few cells developed by the microspore (pollen grain) and remaining within it, and the female gametophyte by a larger group of cells developed by the megaspore (within the ovule) and remaining within it. The same statements are true of the Angiosperms, and the gametophytes are still more reduced in the number of cells. The male gametophyte (within the pollen grain) consists usually of three cells, often represented only by three nuclei (Fig. 113). One of them is the nucleus associated with the development of the pollen tube, and hence is called the tube nucleus; the other two are the sperms (represented either FIG. 113. — Pollen grain (microspore) containing the male gametophyte which consists of three cells or nuclei ; the up- permost nucleus is the tube nucleus ; the two cells, each containing a nucleus, are the sperms. 142 ELEMENTARY STUDIES IN BOTANY by nuclei or naked cells). It would be hard to imagine a gametophyte reduced to lower terms, and it is not at all surprising that the pollen grain was thought to be the male cell, rather than a spore containing a male gametophyte. In fact, no one would have recognized these three cells or nuclei as a gametophyte, if the gametophytes of the Gymnosperms and the Pteridophytes had not been studied. The female gameto- phyte (within the mega- spore that is in the nucellus) at first consists usually of eight nuclei, which become arranged very definitely (Fig. 114). When the megaspore ger- minates to form the ga- metophyte, it ceases to be a, spore, and is repre- sented only by the encas- ing wall that surrounds the gametophyte. The cavity thus inclosed is called the embryo-sac. In other words, we speak of the megaspore until it begins to germinate, and then we call the same cavity an embryo-sac. This name was given before there was any knowledge of the existence of a megaspore or a female gametophyte within an ovule, for it was .seen that the embryo appeared in a sac-like cavity. Within this embryo-sac three of the eight nuclei become placed in the end of the sac towards the micropyle, and are organized into FIG. 114. — The female gametophyte of a lily, having developed within the megaspore, which is within the nucellus of the ovule ; in the end of the embryo-sac (the name given to the megaspore when the gametophyte begins to develop) towards the micropyle (m) is a group of three cells, one of which is the egg (e) ; at the other end of the sac is another group of three cells ; in the midst of the sac the two nuclei are seen which are to fuse and form the endosperm nucleus. SPERMATOPHYTES 143 a group of three naked cells, one of which is the egg. Three other nuclei become placed at the other end of the sac, and may remain as free nuclei or become organized into a group of three cells. The two remaining nuclei behave in a remarkable way, for they come to- gether and fuse to form a single large nucleus, which is called the endosperm nucleus because it produces the endo- sperm, a tissue developed within the embryo-sac to nourish the embryo. A female gametophyte ready for fertiliza- tion, therefore, consists of seven cells or nuclei (Fig. 114) : a group of three at the end of the sac towards the mi- cropyle, one of which is the egg ; another group of three at the other end of the sac ; and the large endo- sperm nucleus (two nuclei fused) lying between. 86. Fertilization. — The act of fer- tilization must be preceded by pollina- FlG> 115. _ Diagram of tion, which is a notable feature of Angiosperms. Among Angiosperms there is a good deal of wind-pollination, but in addition to this there is a re- markable development of insect-pollin- ation. So important and elaborate is this relation between the flowers of Angiosperms and insects that it will be discussed in the following chapter. At this point, all that is necessary to state is that through the agency of wind or of insects the pollen is carried from the stamens to the stigmatic surfaces of pistils, with of course much loss pollen tubes penetrating the style (grains can be seen lying on the stigma) ; one of the tubes has passed through the style, en- tered the ovary cavity, passed along the wall of the ovary, entered the micropyle of the ovule, penetrated the tip of the nucellus, and discharged its two sperms into the embryo- sac ; one of the sperms fuses with the egg, the other with the endo- sperm nucleus. 144 ELEMENTARY STUDIES IN BOTANY of pollen by the way. This landing place of pollen in An- giosperms is very different from that in Gymnosperms. In the latter group the pollen reaches the tip of the nucellus, but in the former group it can reach only the surface of the carpel that incloses the ovules. This means that in Gym- nosperms the male cells (in the pollen grain) are separated from the egg only by the tissue at the tip of the nucellus, while in Angiosperms the male cells are separated from the egg not only by the tissue at the tip of the nucellus, but also by the style and the ovary cavity. After pollination has been accomplished, therefore, there must be an extensive development of the pollen tube before fertilization can be accomplished (Fig. 115). A good pollen grain lying on the stigmatic surface begins to send a tube into the style, and into the tip of the tube the two sperms pass. The growth of the tube is started by a sugary secretion of the stigmatic surface ; it continues its growth down through the style by means of food material supplied by the adjacent cells, enters the ovary cavity, and grows along its wall, enters a favorably placed micropyle, reaches the tip of the nucellus, grows on through the tip of the nucellus, pierces the wall of the embryo-sac, and discharges its two sperms, which at last have free access to the egg. Before fertilization is possible, therefore, there must be pollination and the growth of a pollen tube. It is strange that pollination and fertilization should ever be confused, when they are separated by such an extensive performance as the growth of the pollen tube. In some Angiosperms (and in many Gymnosperms) fertilization does not occur until a year after pollination, and the time interval varies in different plants between a year and a few hours. A remarkable situation is developed in Angiosperms in connection with fertilization. Two sperms are discharged into the embryo-sac by the pollen tube, and there is only one egg. For a long time it was thought that one sperm united SPERMATOPHYTES 145 with the egg, and that the other sperm simply wasted away, accomplishing nothing. Now it is known that while one sperm unites with the egg, the result being a fertilized egg, the other sperm unites with the endosperm nucleus, which then represents a case of triple fusion. This phenomenon of fertilization in the angiosperm embryo-sac has been called " double fertilization." The fer- tilized egg forms the embryo (the young sporophyte), and the fertilized endosperm nucleus forms the endosperm, a tissue that feeds the embryo. FIG. 116. — A, embryo of a Dicotyledon, show- ing the terminal stem tip between the two cotyledons (which therefore arise from the side of the em- bryo) ; B, an embryo of a Monocotyledon, showing the terminal cotyledon, and the stem tip arising on one side ; in both cases the hypocotyl is the other (lower) end of the embryo. FIG. 117. — Seed of violet, the left figure showing the hard seed coat, and the right figure the abundant endosperm that sur- rounds the embryo ; observe the regions of the embryo, namely, hypocotyl, two cotyledons, and a minute plumule (to form the stem with its leaves) between the bases of the cotyledons. — After BAILLON. This double fertilization accounts for some things in con- nection with seeds that were not understood before. It means that the pollen parent can transmit its characters not only to the embryo, but also to the endosperm. For example, if corn with red ears be used as the pollen parent, and corn with white ears as the egg-producing parent, it would be natural to expect a mixture of white and red in the ears of the plant produced by the embryo. But the fact had long 146 ELEMENTARY STUDIES IN BOTANY been noted that the mixture of white and red also appeared in the very ears that had been pollinated, without waiting for the embryo to develop a new plant. This was a mystery until double fertilization was discovered, and it was found that the red color of the pollen parent was in the endosperm, and had been introduced by the sperm that fertilized the endosperm nucleus. 87. The embryo. — The fertilized egg develops the embryo, but in Angiosperms two distinct types of embryo are developed, which give names to the great groups of Angiosperms. In one type of embryo, the tip of the hypocotyl (see § 75, p. 126), which is to give rise to the root, is at one end of the embryo, the stem tip is at the other end, and the cotyledons (see § 75), usually two in number, develop on the side of the embryo just below the stem tip (Fig. 116, A). The Angiosperms having this kind of an embryo are called Dicotyledons, and they are very much the more numerous group. In the other type Of embryo, the hy- pocotyl tip is at one end, the solitary cotyledon is at the other, and the stem tip develops on the side of the embryo (Fig. 116, B). The Angiosperms having this kind of embryo are called Mono- cotyledons. It must not be supposed that the difference between Di- cotyledons and Monocotyledons depends upon the number of cotyledons, as the names might imply, but on the relative position of the stem tip and cotyledon in the two cases. For example, a Dicotyledon, while it usually has two cotyledons, may have more, or it may have only one ; bul if the stem tip is terminal rather than lateral, it is a Dicotyledon. On the FIG. 118. — Pod of sweet pea burst- ing open to dis- charge its seeds. — After GRAY. SPERMATOPHYTES 147 other hand, a Monocotyledon is restricted to one cotyledon because it is a terminal structure, but it must be remembered that an embryo with one cotyledon may belong to a Dicoty- ledon. 88. The seed. — The features of a seed have been described under Gymnosperms (§ 76, p. 127), and they differ in no es- sential way among the Angiosperms. The embryo develops to a certain stage, varying widely in different plants, and then passes into the dormant stage, probably due in large measure to the cutting off of the water supply. Dur- ing the development of the embryo the hard testa develops, protecting the delicate struct- ures within against the exposures of an unfavorable season, as the cold of winter, dryness, etc. (Fig. 117). The seeds of Angiosperms differ widely as to the amount of endosperm left by the em- bryo when it becomes dormant. The endo- sperm in a seed, therefore, may vary from a great deal (Fig. 117) to none at all. For example, in the seeds (" grains ") of cereals (wheat, corn, rice, etc.) a great amount of endosperm is left, and the world gets much of its food from this source ; while in peas and beans no endosperm is left, but the coty- ledons have stored up the food supply taken from the destroyed endosperm and have become bulky, so that in this case we use the cotyledons for food instead of the endosperm directly. 89. The fruit. — While the seeds of Angiosperms are ripening, changes take place also in structures outside the seed. For example, the ovary wall may change and become a hard or parchment-like seed-vessel, as in peas and beans, whose seed-vessels are called pods (Figs. 118 and 119). In other cases, the whole ovary may become a thin-skinned FIG. 119. — Pod of iris ("three- celled") burst- ing open. — After GRAY. 148 ELEMENTARY STUDIES IN BOTANY pulpy mass in which the seeds are imbedded, as in the grape, currant, gooseberry, tomato, etc., all of which are berries. In still other cases, the ovary wall may ripen into two layers, the inner one being very hard and the outer one being fleshy, as in the peach, plum, cherry, etc., which are called stone-fruits (Fig. 120). Sometimes the changes extend beyond the ovary. For example, the cup-like base of the flower sur- rounding the ovary may become fleshy, as in the apple and pear, in which the ovary is represented by the " core " con- taining the seeds (Fig. 121). An extreme case is the pine- apple, in which a whole flower cluster has become an enlarged fleshy mass, in- cluding the axis and the bracts (Fig. 122). All of these changes outside the seed result in what is called the fruit. It is evident that " fruit " is a very indefinite thing. It may be dry or FIG. 120. — Section of a . J peach, showing pulp and fleshy, and it may include only the sseedboxforgerminating seeds. — After BAILEY. SEEDS 325 gardeners use (Fig. 10). In this case such germinating con- ditions as water and temperature can be controlled, so that the accidents of dryness and chill can be avoided at a very critical period. In this way germination is also more prompt than in the ordinary conditions out of doors, so that the young plants get started earlier. Another very important advantage is that the poor seedlings can be discovered and discarded, and only the vigorous, promising ones used in the permanent bed. This enables one to supplement seed selec- tion by seedling selection, and the result is a good, clean, uniform crop. The transplanting of the selected seedlings into properly prepared permanent beds is a simple performance which a little practice will make rapid and effective. The only suggestion needed is that the rootlets of the seedling should be disturbed in their soil connections as little as possible, and so with each seedling there should also be transplanted a little of the soil in which its root is imbedded. Of course seedlings may be pulled out of the soil and transplanted, but time is lost in their recovery from this rough treatment. CHAPTER V OTHER METHODS OF PROPAGATION 30. Vegetative propagation. — Plants can be propagated in other ways than by their seeds, and advantage is often taken of this fact. Among the advantages secured are a more rapid production of plants and a greater certainty that the plants will come true to type. The greater rapidity of pro- duction is secured by eliminating the germination and seed- ling stages, and starting with considerable maturity. In the case of plants of long periods, as shrubs and trees, this shortening of the period between the start and the crop is of great importance. Greater certainty as to the character of the plants produced arises from the fact that a seed has come from the act of fertilization, and this usually involves the characters of two parents; while the other methods of propagation involve the vegetative continuance of one indi- vidual. For example, no one thinks of raising potatoes from seeds to secure a crop. By using the tubers (thickened under- ground stems), new potato plants are secured much more speedily, and the new tubers are like the parent tuber. In addition to seed propagation, therefore, it is necessary to consider vegetative propagation. The principal kinds of vegetative propagation may be included under three heads : (1) cuttings, (2) layering, (3) grafting. 31. Cuttings. — By this is meant that cuttings or " slips," usually of the stem, can be used to produce new plants. A stem is made up of nodes (joints) and internodes (the parts of the stem between the nodes). The nodes have the power to produce lateral members, which ordinarily are leaves and branches ; but when nodes are put in the proper soil condi- 326 OTHER METHODS OF PROPAGATION 327 tions, they can produce roots, also. Therefore, if a node puts out a branch, which is merely a new stem, and at the same time strikes root, a new and independent plant is started. It is evident, therefore, that propagation by cuttings is secured by planting nodes, and that a good vigorous node should be able to produce a new plant, which is a vegetative continuation of the old plant. Not only are cuttings of stems used for propagation, but also in some cases cuttings of roots and leaves. It must be understood that propagation by cuttings is not used with all cultivated plants, and it is not known how many of them could be propagated in this way. Some of the more important plants propagated by cuttings and the general method of procedure may be indicated by a few illustrations. The details differ more or less for each kind of plant propa- gated in this way, and facility in this work can only be secured by learn- ing what is necessary in each case and by practice. A conspicuous illustra- tion of the use of stem cuttings is in the propaga- tion of grapes. In this case the stems of the cur- rent year are secured late in the season, before severe cold, and either stored or made into cuttings at once. When either stems or cuttings are stored, they must be kept in a cool place and prevented from drying out by some such covering as fresh moss or earth. The usual practice in making the cuttings is to include at least two nodes (indicated by buds), the cutting thus being six inches or more long, the upper cut M^?f^^': FIG. 11. — A cutting in position in a trench. — After BAILEY. 328 ELEMENTARY STUDIES IN BOTANY being just above the upper bud. In the spring, the cuttings are planted " right end up," in well-tilled soil, so that the upper bud is at the surface. The cuttings are not planted by being thrust into the soil, but are placed about a foot apart in trenches and covered up (Fig. 11). If the cuttings and the soil and the planting are all what they should be, many of the cuttings will establish plants during a single season, which are then ready for transplanting into a permanent position. These details will vary with different plants, largely depen- dent on the use of young wood or mature wood for cuttings, or on the use of short or long cuttings. In the grape cuttings just described, the cuttings are long and contain ma- ture wood. The best il- lustration of the use of cut- FIG. 12. — Potato tuber, showing the "eyes" which indicate ^jftfrg Q£ nodes, and also some young branches ("sprouts") started. ground stems is in the propagation of potatoes. The potato tubers are thickened underground stems, and their nodes have all the powers of those of aerial stems (Fig. 12). The position of these nodes is indicated by the so-called " eyes," which are young buds in the axils of more or less evident scales (which in this case might be called " eyebrows ") . The cultivation of potatoes will be described later, but in this connection the preparation and planting of the cuttings will be indicated. The tuber is cut in such a way that each piece to be used for planting contains one or two eyes; and at the same time each piece must contain as much food material as possible. The bud (eye) is a young shoot, capable of developing a stem with its leaves, and the node in the proper soil conditions can also put out roots. This means the organization of a new OTHER METHODS OF PROPAGATION 329 plant, but until it is established and independent, it must depend upon the food stored up in the old tuber. It is evi- dent, therefore, that the node, with its bud, must be in con- nection with as much of the old tuber as possible, if the new plants are to start rapidly and vigorously. The depth of planting is different for early and late potatoes, being two or three inches in the former case, and nearly twice as deep in the latter. The character of the soil and the nature of the cultivation for this very important crop will be considered in another connection. The same general prin- ciples, applied with differ- ent details, appear in prop- agating by root-cuttings, as in the case of raspber- ries, sweet potatoes, etc., or by leaf -cuttings, as in the case of begonias. 31 a. Layering. — Propa- gation by layering is really only a modification of propagation by cuttings, the difference being that nodes Of the Stem are made FIG. 13. — Layering a plant, as a rose or rasp- to strike root before they are separated from the parent plant. In case plants can be propagated readily by cuttings, the less convenient method of layering is not used. An outline of the method is as fol- lows : In such plants as certain of the roses and raspberries, a long and flexible young branch is bent down to the ground, fastened in place, and the end carried up and held in an upright position above ground (Fig. 13). The bent portion 330 ELEMENTARY STUDIES IN BOTANY is covered with good soil, which puts some nodes in a favor- able condition for striking root. It facilitates the growth of roots if the bark breaks at the bend ; in some cases it helps to make an incision near the node ; and sometimes a ring of bark is removed. In this way an independent plant may be developed, which in the course of a season or two is in a condition to be transplanted into a permanent bed. 32. Grafting. — The process of grafting is the insertion of a part of one plant into another so that the inserted part grows supported by the other plant. The inserted part is called the scion, and the plant upon which it is grafted is called the stock. The purpose of grafting is to propagate the scion, which represents the desired plant. There are several condi- tions that make grafting a desirable and even a necessary process. For example, in the case of fruit trees, to propagate a desired variety by seed is a long and uncertain process. Even if the time were short between seed-planting and fruit- bearing, often the seedlings do not come true and the fruit is not that which is desired. In the case of seedless fruits, grafting becomes necessary for propagation. Advantage is taken of grafting also to secure varieties of fruits in regions that are unfavorable to scion-plants. For example, peach trees thrive better in sandy soils of the southern states than do plum trees; therefore by using peach tree stocks and grafting into them plum tree scions, the plum varieties can be secured which otherwise would be impossible. It is evident that the use of grafting is based upon the fact that the scion retains its individuality, so far as the character of its fruit is concerned. Much has been written concerning the influence of stock on scion, and of scion on stock, but in ordinary practice this influence is negligible. It is of scien- tific interest to discover how unlike plants may be and still enter into this union, but the fact of practical importance is that the more closely the two plants are related, the more successful is the grafting. OTHER METHODS OF PROPAGATION 331 Grafting is a very old operation, and it has developed into very many kinds. In this connection it would be unprofit- able to describe many methods, for such detailed knowledge is necessary only for those who are making a special study of grafting. A few common methods will be described, and they will serve to illustrate the principles involved. Cleft-grafting is a method very commonly used with fruit trees (apple, pear, plum, cherry, etc.), when it is desired to use well-established stock plants to support varieties with more desirable fruit. The stock plant is cut off at a suitable place, the stump end is split a short distance and wedged, the wedge- shaped base of the scion is in- serted so that cambiums of scion and stock are in contact, the wedges are removed, and the whole surface of the graft is covered with grafting wax, which protects the wound until it has healed and stock and scion have grown to- gether. To double the chances of success it is very common to insert two scions into a single cleft, for the cambium is near the surface, FIG u — cieft-grafting • in the and a scion on each side of the cleft %*£"$£ £UT £ '^Tii Will be in proper position (Fig. 14). covered with grafting wax. — _. . After BAILEY. The scions usually include three nodes (buds), and are cut from twigs of the previous season. These twigs are stored for a time in a cool place and pass into a dormant condition. It is customary to insert the scion so that one of the buds is at the surface of the graft, and this bud, although covered by the grafting wax, has the best chance to grow. The use of a twig as a scion is what is ordinarily meant by grafting, and in addition to cleft-grafting, described above, 332 ELEMENTARY STUDIES IN BOTANY FIG. 15. — Whip-grafting. — After BAILEY. there is whip-grafting, in which scion and stock of equal size are spliced and lashed together (Fig. 15) ; inarching, in which two potted plants, for example, are brought together, and the scion is fastened to the stock without separation from the parent plant until union has been secured ; bridge- grafting, in which the stock is girdled, and dormant scions, wedge-shaped at each end, are inserted at each edge of the girdle and bound in (Fig. 16). 33. Budding. — In addition to the use of twigs as scions, which may be called true grafting, it is very common to use buds as scions, a method which is bud-grafting, but is usually called simply budding. This consists in in- serting under the bark of a stock plant a bud that has been removed from a scion plant. It is performed in spring or autumn, when the bark peels easily, and is frequently used, instead of twig-grafting, in the propagation of desirable races of fruits, especially of the stone fruits. The bud is sliced from its stem so as to include a little of the wood beneath ; the leaves are removed from the stock in the region to be grafted ; cross slits (usually like a T) are made through the bark of the stock ; the base of the bud is slipped beneath the flaps of bark and bound in position ; and in two or three weeks the bud " sets " and the wrapping is removed. All of the operations described in this chapter are merely illustrations of a very extensive practice of vegetative propagation. As opportunity offers, such opera- tions should be witnessed in orchards, nurseries, greenhouses, etc. Furthermore, if suitable plants are available, some of the simpler operations should be undertaken by the students. FIG. 16. — Bridge- grafting. — After BAILEY. CHAPTER VI PLANT-BREEDING 34. Definition. — By " plant-breeding " is meant the im- provement of our old plants and the securing of new ones. Great advances have been made recently in our knowledge in reference to plant-breeding. These advances have largely been due to the fact that scientific men have been experiment- ing with plants to discover what are called the laws of hered- ity, and how new kinds of plants are produced. All this work of scientific plant-breeders has suggested to practical plant-breeders how their methods may be improved. Since a better and a more abundant food supply depends upon the progress of plant-breeding, it is evident that it is a subject of the greatest importance. 35. Seed firms. — The work of practical plant-breeding is done chiefly by establishments that have made it a specialty, and that provide improved races of plants and new plants for the use of those who cultivate them. For example, the farmer seldom works at plant-breeding, but secures his seed from " seed firms " that are equipped to do the more careful work that plant-breeding requires. 36. Department of Agriculture. — In addition to the work of the seed firms, the United States government, through its Department of Agriculture, does a vast amount of work in both scientific and practical plant-breeding, the results of which are for the benefit of all those who wish to cultivate plants. This Department also publishes a great many bulletins dealing with all kinds of operations connected with the cultivation of all kinds of plants, and these bulletins may usually be obtained for the asking. It would be a wise thing 333 334 ELEMENTARY STUDIES IN BOTANY for each school to secure a set of these bulletins dealing with the prominent crops of the vicinity. 37. State Experiment Stations. — The same sort of work and the same free distribution of information is going on at the various State Agricultural Experiment Stations, and the bulletins from the station in its own state should certainly be obtained by each school. Although the national government and the state govern- ments and the seed firms are all at work on the problems of plant-breeding, so that the cultivator of plants may take their results and use them, yet the intelligent cultivator should know something of the methods and possibilities of plant-breeding. This knowledge will at least give him a more critical j udgment in reference to the claims made by the practical plant-breeders. 38. Mass culture. — The oldest method of plant-breeding is called mass culture, a method which has done much in securing improved races of plants. It may be explained by using wheat as an illustration. The plant-breeder selects some feature of the wheat he wishes to improve ; for example, its yield. He goes through a wheat field and selects the indi- vidual plants whose heads bear the largest number of grains. The grains from these selected plants are saved for seed, and in the next season they are planted and produce a crop. The plant-breeder goes through the new field and again selects the best individuals, and their grain is saved for seed. This selection goes on year after year, and each succeeding year shows a somewhat larger yield than the year before. Pres- ently by this method of " continuous selection " the larger yield reaches a standard and a steadiness that enables the plant-breeder to announce an improved race of wheat, that is, a race improved as to its yield. This method of plant-breeding has certain disadvantages that are obvious. It requires a great deal of time and labor, and when the improved race is put into the hands of an PLANT-BREEDING 335 ordinary farmer it does not stay improved very long. Unless the farmer uses great care in his own selection of individuals for seed, he will mix poor individuals with good ones and his succeeding crops will degenerate. For this reason, such farmers must apply frequently to the plant-breeders for a new supply of " guarded stock," that is, seeds from individ- uals that have been carefully selected and kept separate from the undesirable ones. 39. Pedigree culture. — Another method of plant-breeding that has come into prominence more recently is called pedigree culture, which means that a single plant is selected and its progeny carefully guarded, rather than hundreds of plants. It is the method ordinarily used in breeding fine animals. For a long time animals have not been improved by the pas- ture-full, but by the individual, whose pedigree is carefully recorded. It is a well-known fact that no two individuals are exactly alike, so that in even the most careful mass culture many kinds of individuals are mixed, and the result is an average. In pedigree culture it is not an average of many good individuals that is secured, but the very best individual. The advantages of pedigree culture over mass culture are obvious. The selected individual is farther along in the right direction to start with, and so time and labor are saved; and also it is found that the result is more constant and less likely to degenerate. However, the best results are obtained by combining the two methods ; for even after pedigree cul- ture has selected out a desirable race, it may be improved by mass culture. 40. Disease-resistance. — In connection with pedigree culture it has become possible to combat disease and drought with remarkable success. These are the two most serious enemies to cultivated plants, and our annual losses from these two causes are very large. A few notable cases will serve to illustrate the method. 336 ELEMENTARY STUDIES IN BOTANY A few years ago the cotton fields of the southern states were attacked by a very destructive disease. When the ravaged fields were examined by experts, it was discovered that certain cotton plants were untouched by the disease ; in other words, these individuals were immune to this partic- ular disease. This fact suggested that this immunity might be a character that could be inherited, and so immune indi- viduals were selected for breeding, and it was found that their progeny was also immune. In this way, by pedigree culture, immune races of cotton have been developed. It must not be supposed that an immune race is immune under all condi- tions, but this method enormously increases our success in preventing disease. This same method can be applied to all plants for all diseases, so that it is possible to look forward to the time when we will be cultivating only disease-resistant races of plants. 41. Drought-resistance. — A few years ago the wild orig- inal of our cultivated wheat was discovered in Palestine. This wild wheat grows in dry conditions, in situations that we would call " arid/' such as are found in this country in New Mexico and Arizona. A drought-resistant wheat would be of the first importance, provided it was also of good quality. This combination of drought-resistance and good quality has now been secured through plant-breeding, so that it has become possible to insure wheat crops against drought. More than that, the drought-resistant wheat thus secured is found to be disease-resistant ; that is, to the rust disease. This combination of drought-resistance, disease-resistance, and good quality promises to increase greatly the production of wheat. A peculiar race of corn has been found in cultivation in China, which has a structure that makes it drought-resistant. Corn is peculiarly in danger of drought during the period when pollination occurs, and if a " dry spell " occurs at that period the corn crop is seriously damaged. If this drought- PLANT-BREEDING 337 resistant character can be combined with good quality of grain and good yield, the result will be of very great impor- tance. This work is under progress, but the results have not been announced. These illustrations from wheat and corn, our two most im- portant cereal crops, indicate the possibility of breeding drought-resistant races of all the important cultivated plants. 42. Corn-breeding. — It would not be fair to give the impression that plant-breeding is a simple problem and that all plants can be handled alike. The breeding of corn will serve to illustrate how difficult the problem often is. A great deal of corn-breeding has been done, and it is still one of our most important problems, for corn is not only one of our most important cereals, but it is probably the most difficult one for the plant-breeder to handle. The ordinary field of corn is a remarkable mixture of different kinds of individuals, so that ordinary mass culture reaches very indefinite results. The discovery that the best method of selection is to select the best ears rather than merely the most vigorous individuals has resulted in a very largely increased yield. One difficulty in connection with corn, however, is that pollination is so free that under ordinary conditions it is beyond control. During the four or five days when a young ear is being pol- linated, the pollen is flying freely from the tassels of many plants, so that some of the kernels of an ear may have received undesirable pollen. Therefore, after a good ear has been selected for seed, it may contain undesirable hybrid kernels. This means that selection must be continuous, not only to secure desirable individuals, but also to weed out undesirable hybrids. It is obvious that in this case pedigree culture deals with pedigrees known on the female (ear) side and only vaguely known on the male (tassel) side. When rigid pedigree culture is applied to corn, so that pol- lination is accomplished under control, and a pure strain is secured, free from all mixture with other kinds of individuals, 338 ELEMENTARY STUDIES IN BOTANY it has been found that this pure strain deteriorates to a cer- tain level ; in other words, it is not so good for our purposes as the mixed races. In this case it is found that if two pure strains are crossed, the resulting hybrids are more vigorous than either parent. The ideal corn-breeding, therefore, is rather a complex operation, involving two distinct operations : (1) pedigree culture, which separates pure strains from a mixture; (2) combination of pure strains, which secures vigorous plants. The question might be asked, why is it desirable to separate pure strains from mixtures, only to combine them again in new mixtures? The answer is that unless the pure strains are separated and recombined, the mixtures are chance mixtures rather than intelligent mixtures. There are very many people, however, who prefer to use chance rather than intelligence. 43. Hybridization. — In the operations of plant-breeding described above, reference was made to " crossing " ; that is, the use of two parent plants of different kinds, resulting in what is called a hybrid. Hybridization is a very important operation in plant-breeding, for by means of it certain desir- able qualities that are separated in two kinds of plants may be combined in a single individual. It must not be supposed that the desired combination will appear in all of the hybrid progeny. It is only when thousands of hybrids are produced that there is any certainty that the desired combination will be found among them. But when it is found, the plant possessing it can be pedigreed and multiplied. There is a limitation in the use of hybrids that must be noted. A hybrid combines characters of two parents, and when it produces progeny by means of seeds, only about one- half of the new individuals will continue the combination, that is, will continue to be hybrids. The other half will resemble one or the other parent. This is what is called the " splitting " of hybrids, and they split up in a definite ratio, which is called Mendel's law, and this same ratio of PLANT-BREEDING 339 splitting appears in each succeeding generation. In propa- gating a hybrid by seed, therefore, one may expect that in ordinary conditions only about one-half the progeny will show the desired combination. It follows, therefore, that hybridization is most useful with those plants that are not propagated by seed, but by some vegetative method, as by tubers, bulbs, cuttings, layering, grafting, etc. ; for in these cases one hybrid individual is continued directly in its progeny, without bringing in another plant as a parent. It is evident that the method can be used with great efficiency among the fruits, which are so largely propagated vegetatively ; but that it is by no means so efficient among the cereals, which must be propagated by seeds. A few illustrations will fix the method in mind. Seedless apples of poor quality have long been known, but by crossing seedless apples with those of good quality, a hybrid was pro- duced which combined the two desired characters. It is evident that in this case vegetative propagation is necessary, so that there would be no danger of the hybrid splitting in the ordinary way. The ordinary cultivated blackberry is large and black, but there is a small wild blackberry that is whitish or cream color. By crossing the two, a hybrid was secured that pro- duced berries of the large size and light color, so that " white blackberries " could be grown. The possibilities of such combinations are endless and many of them have been made, some more curious than useful, but many of them very useful. Enough has been said to show that the operations of plant- breeding are exceedingly varied, and that by the use of various methods, either singly or in combination, almost any desired result may be obtained. It is becoming almost literally true that one may order almost any kind of plant and expect to have the order filled. 340 ELEMENTARY STUDIES IN BOTANY 44. Selection for regions. — One important fact con- nected with plant-breeding needs to be emphasized. The natural tendency is for cultivators of plants to attempt to grow the same kinds of plants everywhere. If natural vege- tation is observed, it will be observed that the assemblages of plants, technically known as the " plant population," differ in different regions, which means that nature does not attempt to grow the same plants everywhere. It is obvious that for every region there is the most suitable group of culti- vated plants, that is, plants that will do the best. If this is considered, each region can be made to yield its maximum of plant products, which would greatly increase the total production of a large country like the United States. 45. The food problem. — The food problem is one of the most important problems of this country. It has become a problem because the rate of increase of population is much larger than the rate of increase of food production. It is evident that this inequality of the two rates must not be allowed to continue indefinitely. The recent developments in plant-breeding, indicated in the preceding paragraphs, together with the increase of knowledge in reference to the nature of the soil and its manipulation, outlined in Chapter III, make it possible to multiply many times the plant prod- ucts of the country. This becomes evident if the following possibilities are realized : 1 . Securing plants of largest yield and most desirable qual- ity through the various methods of plant-breeding. 2. Securing disease-resistant races, by means of which frequent and great loss in plant products can be prevented. 3. Securing drought-resistant races, by means of which crops can not only be insured against drought where they are grown now, but their cultivation can be extended into new regions, especially those which have been regarded as too dry for such plants. 4. Selection for each region of the group of cultivated PLANT-BREEDING 341 plants best fitted for the conditions, by means of which the maximum yield of plant products can be secured for each region. 5. Cultivation of the soil in such a way that it may be kept in the best physical condition from the time of planting to the time of harvesting. Experience has shown that when any one of these five possibilities is realized, the amount of plant product is much increased ; and it becomes evident that when all five of them are realized throughout the country, our food production will be multiplied many times. Another important factor that enters into the explanation of our diminishing food supply in comparison with our popu- lation is the persistent movement of population from the country to the cities, changing producers of food into mere consumers of food. Now that agriculture is becoming as scientific a profession as engineering or medicine, it is to be hoped that it will be attractive to an increasing number of vigorous young men, who might well recoil from the blind drudgery of the old-time farm, but will welcome the new and highly important science of agriculture. 23 CHAPTER VII CEREALS AND FORAGE PLANTS CEREALS 46. General statement. — The cereals must be regarded as the most important crop plants of the world. They are grasses that have been brought into cultivation on account of the abundant starch stored in their seeds. This starch is not only the basis of our." bread-stuffs/' but it also feeds the animals from which we obtain our principal meat supply, as well as those we use in other ways. The cultivation of cere- als is the chief business of agriculture, so far as plants are concerned, and among the cereals are plants that have been cultivated throughout the whole recorded history of man. In fact, it was probably the cultivation of cereals, more than any other cause, that first transformed wandering tribes of men into settled, agricultural people. The important cereals are corn, oats, wheat, barley, and rye, and the order given represents their relative importance in the United States at the present time. In considering the cultivation of cereals in the United States, the student should know not only the methods of cul- tivation, but also the range of cultivation and the relative importance of each crop. The statistics given have been obtained from the most recent information in possession of the United States Department of Agriculture. They are given in round numbers, but they will reveal the relative importance of our cereals as at present cultivated. It must also be remembered that the amount of production varies from year to year, dependent upon what are called " good 342 CEREALS AND FORAGE PLANTS 343 years " and " bad years " for such crops. The cereals will be considered in the order of their importance in the United States. Corn (Maize) 47. Production of corn. — A more appropriate name for Indian corn is " maize," the original name given to it when America was discovered. In foreign countries, " corn " means any grain and several things besides. " Indian corn " FIG. 17. — Map shaded to show the states of greatest corn-production. distinguishes it from any other grain, but the simple word " corn " distinguishes it only in the United States. The United States is preeminently the country of corn-pro- duction, in 1912 producing over three billion bushels. This statement is emphasized by contrasting this production with that of other countries, which will have to be done for the year 1911. In that year, a relatively poor year, the United States produced two and a half billion bushels of corn, while Italy, the second country in corn-production, produced 93 million bushels, and Russia 81 million bushels. In fact, in 1910 (the 344 ELEMENTARY STUDIES IN BOTANY last year for which returns from all countries are available), the United States produced nearly three-fourths of the corn of the world, a ratio which prob- ably still holds. The greatest corn-producing state is Illinois (about 335 mil- lion bushels in 1911), and the record for Iowa is almost as large (about 305 mil- lion bushels in 1911). No other states were re- ported as pro- ducing more than 200 million bushels in 1911, the order of the larger records being Missouri, Indiana, Ne- braska, Ohio, and Kansas. In the government statistics re- ferred to, 18 states are included as corn-producing states, the remaining 11, in the order of amount of production, being Kentucky, Tennessee, Minnesota, Texas, Pennsylvania, Georgia, Wisconsin, Michigan, Mississippi, Alabama, and South Dakota. This enumeration of states emphasizes the fact that "the com lands occur in the central and southern FIG. 18. — Corn : the plant at the right shows the stami- nate flowers forming the terminal "tassel" ; the plant to the left shows the "ear" (a close cluster of pistillate flowers) in the axil of a leaf and enclosed by the "husk," at the end of which the long styles ("silk") are exposed. — After CEREALS AND FORAGE PLANTS 345 states, or practically within the drainage system of the Mississippi River (Fig. 17). 48. Structure of corn. — Any one who cultivates corn should know something of its structure, which is quite dif- ferent from that of the other cereals (Fig. 18). There are two kinds of flowers, one containing the stamens and the other the pistil. The staminate flowers form a spreading cluster at the top of the plant, constituting what is commonly called the " tassel." An examination of this tassel shows that it is made up of numerous small flowers, each one of which con- sists of bracts enclosing three stamens whose anthers are soon seen hanging downward, suspended by the long and slender filaments. The flowers with the pistils are in a close cluster upon a branch from the axil of a leaf. It is this branch that forms the " cob," and upon it the pistillate flowers stand close together in longitudinal rows. The branch is ensheathed by large bracts, which later form the " husk " that invests the ear. Each flower consists of small bracts enclosing a single pistil, whose long, thread-like style forms the so-called " silk." It is the silk that receives the pollen from the stamens, and through the silk the pollen tube carries the male cell to the egg. In this way fertilization occurs, and as a consequence the grains begin to develop and later the mature " ear " is formed. The danger from drought occurs when the pollen is flying, for at that time the silk must be moist to receive the pollen and to start the growth of the pollen-tube. Since four or five days are consumed in fully pollinating a single ear, which means that each silk must catch and hold some pollen, it is evident that a drying wind, or even dry air, will endanger the process. This is the most critical period for the corn crop, for blasted silk means failure of fertilization. 49. Cultivation of corn. — In the cultivation of corn, only general principles can be mentioned here. There are many 346 ELEMENTARY STUDIES IN BOTANY details that develop and should be learned in connection with the practice. The cultivation of no cereal has received so much attention in recent years, and, as a result, it is neces- sary for the corn-grower to keep informed as to the results of experimental work. Even the preparatory ploughing varies as to time and depth and other details. While corn is grown on a great variety of soils, the best corn is produced upon deep, rich, well-watered and well-drained soils. A rich soil usually means one with a large amount of organic material in such condition that it is loose and friable, and not likely to cake in dry weather. A soil with such physical properties is often described as a " sandy loam." It has great capacity for -receiving water and retaining it as soil films, and at the same time drains so readily that the circulation of the air is not interfered with. The depth and perfect physical condition of the soil demanded by successful corn-production is greater than for any other cereal crop. In preparing such a soil for seed, it is usually ploughed deeper than for any other cereal crop, but it is not certain that this is necessary. In the greatest corn-producing states, the deeper, pre- liminary ploughing is generally done in the fall, and during the following May the seed-bed is finally prepared and planted. The time of planting is planned so as to escape the late spring frosts. The sowing is done either in hills or drills, but in any event it is done so that the soil can be worked between the rows of corn. The ground is kept pulverized with the harrow until the young plants appear ; and afterwards the same pulverizing is accomplished by running cultivators of various kinds between the rows. This is continued as long as it can be done without injury to the plants, usually extending for about six weeks from the first of June. 50. Selection of corn. — Very much attention has been paid to the selection of seed corn, and to arouse interest and to develop facility in selection, as well as to stimulate interest CEREALS AND FORAGE PLANTS 347 in agriculture in general, there has been an extensive organ- ization of " corn clubs " for boys in rural communities. Reference has been made to these clubs (p. 320), but in this connection the principles of selection will be outlined briefly. The two chief factors in the selection are a suitable plant and a suitable ear. The plant should ^ be vigorous, with all its members (roots, stem, and leaves) well developed. The selected ear should be early maturing, large, sound, well shaped (carrying its diameter well from butt to tip), with straight and compact rows of grains, and a cob about one- half the diameter of the ear (Fig. 19). The selected ears should be stored in a dry place, with uniform temperature ; and be- fore planting the grains should be tested for vitality in a germi- nating bed, usually called a " tester." The direction for club work is that no lot of grains should be used for planting that do not Show by the testing Of FIG. 19. — Two ears of corn, showing a samples that at least 95 per cent of them germinate promptly and vigorously. 51. Corn-tester. — There are several kinds of testers, but one that can be constructed in any school or home is the "sawdust box," which is exceedingly satisfactory (Fig. 20). A box three or four inches deep and about thirty inches square is recommended as a good size. This is half filled with thoroughly moistened sawdust (soaked for at least an hour), pressed down and with a smooth surface. Upon the sawdust 348 ELEMENTARY STUDIES IN BOTANY FIG. 20. — The "sawdust box" for testing corn : explained in text. — After Iowa State College Bulletin. surface is laid a strong white cloth ruled in numbered squares with sides two or three inches long. This cloth is held in place by being tacked to the box. As many ears of corn can be tested as there are squares on the cloth, and each ear must bear a number corresponding to a numbered square. From each ear six kernels are removed : one from near the base of the ear, one from the middle, and one from near the tip, and three others in the corresponding positions on the opposite side of the ear. These six kernels, selected as samples of the entire ear, are placed upon the square of cloth whose number corresponds to that of the ear. When all the kernels to be tested have been placed in their proper positions on the cloth, another cloth is laid over them and sprinkled. Then another cloth, larger than the box, is placed upon the sprinkled cloth, shaped as a lining to the box, and covered with two inches of moist and pressed-down saw- dust, over which the edges of the large cloth are folded (Fig. 20). If kept in a warm place, the grains will germinate in about six days, when the cover is removed carefully so as not to displace them. The condition for examination is when shoots (stems) are about two inches long, and if it is discovered that the grains have been uncovered too soon, the covering should be replaced. Each ear is repre- sented by six kernels, and if one or more of the kernels have FIG. 21. — Section of a grain of corn : explained in the text. — After FRANK. CEREALS AND FORAGE PLANTS 349 failed to germinate, or some of the seedlings are decidedly weaker than the others, that ear should be discarded. The germination of corn is illustrated in Figs. 21-27. In Fig. 21 is shown a section of a grain of corn. Within the testa, the contents are divided into two principal regions, that to the right and below being the embryo, and that to the left and above, the endo- sperm, in which the food is stored. The position of the embryo is peculiar, for in- stead of being surrounded by the endo- sperm, it lies to one side of it. It will be noticed that the single large cotyledon of the embryo is in contact with the endo- sperm, from which it obtains food which it passes on to the growing parts that are to escape from the seed. In the embryo may also be seen the bud that is to produce the stem and leaves, and below it the hypocotyl that is to escape first and estab- lish the root system. The cotyledon is attached at the joint which separates the young stem and the hypocotyl. The figure also indicates that the endosperm has two regions : the outer region (more deeply shaded) is the " horny endosperm," which contains protein food in addition to its starch ; while the inner region (with lighter shading) is the " starchy endosperm." As the relative size of the two regions varies, the richness of the grain in protein or in starch varies. Figures 22 and 23 are slightly different views of a sprouting grain, showing the superficial position of the embryo, and that it simply splits a membrane (the testa) to be completely exposed. Figures 24-26 are all in the same position, Fig. 24 showing the tip of the hypocotyl turning towards the ground ; Fig. 25 showing the great elongation of FIGS. 22 and 23. — Two views of sprouting grains of corn, show- ing the relation of the embryo to the food supply ; the "sprout" is the tip of the hypocotyl. 350 ELEMENTARY STUDIES IN BOTANY the hypocotyl, the beginning of growth and curving upward of the stem, and the putting out of roots ; while in Fig. 26 the growth of all the parts has pro- ceeded still further. In Fig. 27 is shown a young seedling established for inde- pendent work, with the root system started and the leaves beginning to unfold. The value of testing for vitality be- fore planting is indicated by the follow- ing statement from a recent bulletin (February, 1913) issued by the State Agricultural Experiment Station of Iowa: " Testing the vitality of seed corn be- fore planting in- creased the profits per acre 93.6 per cent in 1910 and gg 7 c nt m 191 1 , or an increase of 19.6 bushels per acre in 1910 and of 10.1 bushels in 1911." 52. Sweet corn — In addition to field corn of various kinds, there are the numerous races of sweet corn. Sweet corn is to be regarded as a vegetable rather than a cereal, but the soil condi- tions and the principles of cultivation are the same as for field corn. It is more intensively cultivated than field corn, and to this end it is planted in hills rather than drills, so that the soil all about it may be kept in condition. Canned sweet corn has become so common a food in North America that the demand for it FIGS. 24-26. — stages in the germination of corn: explained m the text. FIG. 27. — A young corn seedling just after ger- mination has been completed. CEREALS AND FORAGE PLANTS 351 has developed extensive cultivation of sweet corn for this pur- pose, the leading states in the amount of this product being New York, Maine, Illinois, and Iowa, in the order named. Oats 53. Production of oats. — The United States is also the leading country in the production of oats, in 1912 producing nearly one and a half billion bushels. The contrast with other FIG. 28. — Map shaded to show the states of greatest oat-production. countries may be illustrated by the crops of 1911, when the United States produced 922 million bushels, and Russia pro- duced 858 million bushels. These two great oat-producing countries were followed by Germany with 530 million bushels. Within the United States, Iowa and Illinois produce the largest amount, in 1911 Iowa producing 126 million bushels and Illinois 121 million bushels. This represents a little over one-quarter of the amount produced by all the states. The other states reported as oat-producing states, in the order of the amount of production, are Minnesota, Wisconsin, Ohio, 352 ELEMENTARY STUDIES IN BOTANY and North Dakota. This means that the states of the Upper Mississippi Valley region produce most of our oats (Fig. 28). 54. Structure of oats. — The structure of oats is more like that of the ordinary grasses than is the structure of corn. The flowers are in a loose, branching cluster (panicle), each little group of flowers (spikelet) with a stalk of its own (Figs. 29 and 30). Each spikelet consists of two relatively large bracts (glumes) that sur- round usually two flowers (Fig. 30, B). Each flower consists of a pistil (whose ovary becomes the grain) and three sta- mens infolded by a bract (palet) , and usu- ally the palet of one of the flowers bears on its back (Fig. 30, C) a long, bristle-like appendage (awn). It is these awns that in many grasses, as the other cereals, form the so-called " beard." The prominent feature that distinguishes oats from wheat, barley, and rye is the loose, branching cluster of stalked spikelets. In these other cereals the spikelets stand close together on the main axis, forming the cluster called a spike, which is the so-called " head " of wheat, etc. FIG. 29. — Oats, showing 55. Cultivation of oats, — The oat is a general habit of plant ; , , . „ . i v flower cluster distin- hardy cereal, doing well in a cool climate ShtabnychSgg S and upon a light soil, and therefore it is each spikelet on a sien- o-rown chiefly in northern countries. In der stalk. J fact, it is not at all suited to the ordinary tropical conditions. The range of conditions in which it will grow is somewhat extensive, including light soils and heavy CEREALS AND FORAGE PLANTS 353 soils, cool climate and warm climate, but it is not able to endure an excess of water. In connection with the sowing of oats, the soil is not always ploughed when it is rich and deep, as corn land, but the seeds are sown broadcast and then covered by means of a corn- cultivator or a spe- cial harrow, being smoothed over after- wards by an ordinary harrow. Upon gen- eral principles, how- ever, a good seed-bed should be prepared by ploughing, not neces- sarily so deep as for other cereals, and pul- verizing. Most of the oats are sown early in the spring, so that most of the growth, which takes approxi- mately three months, FlG 30._Oats> showing detaila of flower clus~ter: AI may occur during the cooler part of the growing season. Oat3 are also sown in the fall (" winter oats "), but this practice seems to be restricted to the more southern areas of oat-cultivation. part of the cluster, showing the stalked spikelets ; B, a single spikelet, showing the two glumes enclos- ing two flowers (a third abortive one is shown), each consisting of a pistil (whose branching style is shown) and three stamens infolded by the palet ; C, the palets of the two flowers, one of them with a long awn. — After SARGENT. Wheat 56. Production of wheat. — It is perhaps a surprise to some that the United States produces less wheat than oats, the amount for 1912 being 730 million bushels. Nevertheless, 354 ELEMENTARY STUDIES IN BOTANY it produces more wheat than any other country, Russia being second, and India third. In 1911 the product from these three countries was 621 million bushels in the United States, 509 million bushels in Russia, and 369 million bushels in India. Within the United States, North Dakota produces the most wheat (about 73 million bushels in 1911), and the other wheat-producing states come in the following order : Kansas, FIG. 31. — Map shaded to show the states of greatest wheat-production. Washington, Minnesota, Illinois, Nebraska, Ohio, Missouri, Indiana, Michigan, and Pennsylvania. It will be noticed that these are all north central states excepting Washington (Fig. 31). 57. Structure of wheat. — It is easy to distinguish wheat (Fig. 32), with its spikes (heads), from oats, with its panicles (spreading clusters) ; but barley and rye also have spikes, and one should be able to distinguish wheat at sight from these cereals. Wheat and rye are alike in having a single spikelet at each joint of the axis ; while in barley each joint bears three spikelets (one or two of which may be poorly developed). CEREALS AND FORAGE PLANTS 355 The most obvious distinction between wheat and rye is that in wheat each spikelet contains several perfect flowers, while in rye each spikelet contains two perfect flowers. There are many races of wheat, but the conspicuous difference in the heads is that some are " bearded " (with awns) and some are " beardless " (without awns) (Fig. 33). 58. Discovery of wild wheat. — The cul- tivation of wheat is the oldest recorded agricultural operation, and wheat is per- haps still to be regarded as the most valu- able of cereals. The wild original of the wheat was long sought for, and it was sup- posed that it had been so long in cultiva- tion that it must have become very much changed and probably was represented in nature by some inconspicuous grass. It seemed clear that if wild wheat still existed, it would be found in western Asia. A few years ago a Jewish botanist found the wild original of wheat growing upon the rocky slopes of the mountains of Palestine, and it did not look very different from culti- vated wheat. It is clear now that our an- cestors who began the cultivation of wheat did not select an inconspicuous grass, fore- seeing that it might be changed into a very useful plant, but took a grass that was plainly useful already. In fact, this wild wheat is a better plant for our purpose in several par- ticulars than our cultivated races. It grows in thin and dry soils, quite unlike the soil necessary for the cultivated races of wheat, which have become pampered by being transferred to better soils. Not only is this wild wheat drought-resistant, but its vigor is further shown by the fact that it is not sus- ceptible to the attack of the rust disease, one of the most FlG. 32. — Wheat, show- ing general habit of plant ; the flower cluster is a spike. 356 ELEMENTARY STUDIES IN BOTANY destructive diseases of our pampered and weakened races of wheat. It is obvious that this discovery of wild wheat, with its drought-resistant and disease-resistant qualities, is full of possibilities in the development of races of wheat suitable for the drier regions of our country, thus enormously extending the area of wheat-cultivation. In certain parts of these arid regions, what is called " dry farming " has been developed, which means the retention of moisture in the soil by proper tillage; and in these regions a race of wheat called " Durum " has been used with marked success. This Durum wheat is a race that is more closely related to wild wheat than any other cultivated race, and for this reason it is more drought- resistant than the ordinary races. 59. Cultivation of wheat. — Wheat has been cultivated for so long a time and under so many conditions that it has more varieties or races than any other cereal, and to select the best race of wheat for a given area demands the judgment of an expert. There are spring and win- ter wheats, bearded and beardless wheats, soft and hard wheats, etc., and new races of all of these are being announced almost every year. . The cultivated wheats require good soil, better than oats will thrive in, and a thoroughly pulverized soil, so as to secure a high degree of water-holding capacity, and at the same time good drainage. In preparing the soil for winter wheat, it is ploughed four or five inches deep, then pulverized, and allowed to settle before the seed is sown. The seed is often sown broadcast and then covered with a harrow, but more commonly now it is drilled, a method which secures more even distribution and more uniform depth. Wheat is a hardy plant in enduring cold, FIG. 33.— "Bearded" and "beardless" wheat. — After Internat. Encyl. CEREALS AND FORAGE PLANTS 357 but the best protection of young winter wheat is a covering of snow, under which it can endure freezing temperatures. The greatest danger to winter wheat is the alternate thawing and freezing of an unprotected soil. Spring wheat is sown as early as possible, to secure the cooler part of the growing season for the principal growth, and usually upon soil that has been ploughed the previous autumn, or often without ploughing upon a corn-field of the preceding FIG. 34. — Map shaded to show the states of greatest barley-production. season. In the case of ploughing and preparing a seed-bed, the seed is broadcast or drilled as described above. In the case of planting among corn-stubble, it is broadcast and covered by a corn-cultivator and frequent harrowing. Barley 60. Production of barley. — The great barley-producing country of the world is Russia, which reported 411 million bushels in 1911 ; while the United States came second with only 160 million bushels. In 1912 the United States, produced 224 million bushels. 24 358 ELEMENTARY STUDIES IN BOTANY Within this country, California produces the most barley (about 40 million bushels in 1911), and the other barley-pro- ducing states come in the following order : Minnesota, North Dakota, Wisconsin, Iowa, Washington, Idaho, and South Dakota. It is evident that the production of barley is not re- stricted by suitable conditions, but by lack of general interest (Fig. 34). 61. Cultivation of barley. — Barley is also a cereal of very ancient cultivation, and has been found in its original wild state in western Asia (Fig. 35) . Its range of cultivation is very great, extending far- ther north than the usual range of wheat, and extending southward into tropical conditions. It also grows quickly, and therefore can be used in regions of short growing seasons. The soil conditions and preparation are approximately the same as for wheat. Most of our barley, at least in the northern states, is sown in the spring. Barley is a little more sensitive to cold than wheat, so that in regions where wheat, oats, and bar- ley are grown, the order of planting is first spring wheat, then barley, and finally oats. The methods of sowing (broadcast and drill) are the same as for wheat. FlGin3g5g7nerlrieh^t°^f The cultivation of winter barley is in- piant and character creasing rapidly, because it gives a better of spike. . . . . yield than spring barley, and is a more certain crop. At present its cultivation is chiefly in the states south of the Ohio and Platte rivers and those west of the Rocky Mountains. The Department of Agriculture has indicated those states in which only spring barley can be CEREALS AND FORAGE PLANTS 359 grown, those in which only winter barley can be grown, and those in which both can be grown. Rye 62. Production of rye. — The United States makes its poorest showing, so far as cereals are concerned, in the culti- vation of rye, coming fifth in the list of rye-producing coun- tries. Russia is far in advance of any other country, with FIG. 36. — Map shaded to show the states of greatest rye-production. 762 million bushels in 1911, followed by Germany with 427 million bushels, then Austria-Hungary, France, and the United States (33 million bushels). In 1912 the United States produced 35 million bushels, the most productive state being Wisconsin, followed by Michigan, Minnesota, Pennsylvania, New York, New Jersey, and Indiana (Fig. 36). 63. Cultivation of rye. — Rye seems to have been intro- duced into cultivation later than the other cereals, for the records of it do not extend beyond the Roman agriculture. For this reason, probably, there are fewer kinds of rye than 360 ELEMENTARY STUDIES IN BOTANY of any other cereal (Fig. 37) . Its great feature in cultivation is that it will grow in soil too poor for any other cereal. It cannot grow so far north as barley, but it can ripen in lati- tudes too cold for wheat. However, it thrives best where wheat thrives, but as it is not so valuable a crop, it does not replace wheat. It is usually cultivated on light, sandy soils, not doing at all well on wet and heavy soils. As in the case of the other cereals, there are spring and winter ryes, the latter being most frequently used, and usually ripening in June. The preparation of the soil, the planting, and the cultivation are the same as for the other cereals. Rice 64. Production of rice. — If the impor- tant cereal crops of the whole world were being considered, rice would have to be added, for it is estimated to supply the principal food of one-half the human race. But very little of the rice of the world is produced in the United States (715 million pounds in 1911), and its production is re- stricted practically to the Gulf states and Arkansas, with Louisiana producing by far the largest amount (Fig. 38) . The greatest rice-producing country in the world is India (about 89 billion pounds in 1910), and Japan is the next in our records (about 15 billion pounds in 1910). The statistics of rice-production in China are not available, but it must be much greater than that of Japan ; and Egypt is also a great rice-producing country. 65. Structure of rice. — The appearance of the flower cluster of rice is intermediate between that of barley and oats (Fig. 39). The spikelets are in a panicle, as in oats, but the FIG. 37. — Rye, show- ing general habit of plant (upper part of stem omitted) and character of spike. CEREALS AND FORAGE PLANTS 361 branches of the panicle are erect and often crowded, not spreading, as in oats, but not compact and looking like a spike, as in barley. There is a single perfect flower in each spikelet, and the hard palet encloses the grain so closely that it falls with it, forming the so-called "husk" about the grain (Figs. 40 and 41). Rice with the husks on is often called " paddy," while in India all rice is " paddy." FIG. 38. — Map shaded to show the states of.greatest rice-production. 66. Cultivation of rice. — The cultivation of rice belongs to subtropical countries, and it requires wet soil, which can be artificially flooded at certain times. There are also " upland " varieties which do not require flooding. In the warmer countries two crops a year are raised. The seed is sown on very wet soil, then transplanted to its permanent place, and flooded at intervals. In the United States the rice lands are prepared as for other cereals, and either put under irrigation control, or lowlands are used that are subject to flooding. Of course the upland rice is cultivated in the dry way used with other cereals. 362 ELEMENTARY STUDIES IN BOTANY FOKAGE PLANTS 67. Definition. — Forage plants are those used as food for farm animals, and their cultivation forms a very important part of agriculture. Foods for animals have been developed recently in such variety that they have extended far beyond the range of forage plants, but the latter are the only animal foods that come within the pur- pose of this book. Forage plants also include those that are not cultivated primarily as animal foods, as, for example, the use of corn fodder, straw, and cereal grains as such foods. These have been considered under the head of cereals. 68. The grass family. — The most ancient forage plants are the grasses,, and every one is fa- miliar with their use for grazing and for hay. Until recently, hay always meant dried grass, but other kinds of hay (dried plants) have been added. Naturally the grasses are still the most used forage plants, for pastures (for grazing) and meadows (for cut- ting) occur extensively in nature and involve the least amount of cultivation. Conspicuous among the grasses that have been Cultivated for pasture and meadow purposes are redtop, timothy, and Kentucky blue grass, and samples of these three grasses should be examined, so that they can be recognized. 69. The legume family. — In addition to the grasses, there FIG. 39-41. — Rice: Fig. 39, the flower cluster; fig. 40, a single flower, with its bracts; fig. 41, bracts removed, showing the grain infolded by the husk. — The single flowers after BAILLON. CEREALS AND FORAGE PLANTS 363 are three great forage plants, which are used also for other purposes. They are clover, alfalfa, and cow-pea, and any outline of agricultural operations which does not include these great crops would be incomplete. They all belong to a single great family (Leguminosse) , and associated with them are such familiar plants as sweet peas, common peas, beans, peanuts, and such trees as the locusts and redbuds. These three forage plants have a very important character in common, which can be described for all of them. They are all able to use the free nitrogen of the air by their peculiar association with the nitrogen-fixing bacteria of the soil. This means that instead of drawing upon the very important nitrates of the soil, they can add to the nitrates and thus enrich the soil. For this reason they can be used to restore soil that has become impoverished in its nitrogen supply by other crops. It is customary, therefore, to alternate crops of these clover-like plants with other crops, notably the cereals, the process being called " rotation of crops." In other words, these forage plants are very commonly used as the " alternating crop " which restores the soil to good condition. These plants are not only useful in adding nitrogen com- pounds to the soil, but they are also remarkably deep rooted and leave the soil in better physical condition. The deep- rooting not only puts the soil in better physical condition, but it facilitates the movement of salts towards the surface, so that the result of such a crop is not only an accumulation in the superficial soil of nitrogen compounds, but also of other important soil salts. Another very common use to which these plants are put, a use which depends upon their rich contents of valuable salts, is what is called " green manuring," which means that the plants are ploughed into the soil and contribute their whole bodies to enriching it. 70. Clover. — There are a good many clovers, but the most valuable one as a forage plant is the red clover, whose 364 ELEMENTARY STUDIES IN BOTANY FIG. 42. — Red clover. appearance, with its three leaflets (each usually with a pale spot on the upper surface) and head of rose- purple flowers, should be familiar to every one (Fig. 42) . It is extremely valuable for the many purposes it serves, such as hay, green fodder, pas- turage, green manuring, but its chief value is in enriching the soil, as de- scribed above. It is used also as a " cover-crop" in orchards, which means that it can cover the soil in such a way as to hold the moist- ure, at the same time enriching the soil. Later it is " ploughed under/' and it contributes still more to the soil. Red clover can grow in a variety of soils and climates, but at present its most extensive agricultural use is in the northern states. 71. Alfalfa. — This forage plant (called also lucerne), a native of western Asia, and long cultivated in Europe, has become extensively cul- tivated in the western states (Fig. 43). It was introduced into Cali- fornia about sixty years ago, and its cultivation has extended rapidly over the arid regions of the Pacific and FIQ 43. _ Alfalfai showing the Rocky Mountain States, where it is ^ general habit, a single flower, , , and the curiously coiled pod. grown more extensively than any —After in. of British Flora. CEREALS AND FORAGE PLANTS 365 other forage crop. Its cultivation is extending still further east, and it bids fair to replace red clover in many of our northern states. The best soil for alfalfa is a rich, sandy, well-drained loam, and this makes it especially favorable for the rich soils of the dry west where irrigation is used. It is a plant one to three feet high, with clover-like leaves, and purple flowers in long, loose clusters. In loose soils the tap-root is said to reach a FIG. 44. — Cow-pea. — After ENGLER and PRANTL. depth of ten to twelve feet, and cases of 50 feet in depth have been reported. The seeds are sown broadcast or in drills, and the young plants are rather tender, so that care is necessary to establish a field, which usually requires two years, but after it has been established it is quite enduring. The ordinary yield of hay is reported to be three to eight tons per acre, and sometimes a yield of ten to twelve tons per acre is reached. 72. Cow-pea. — Cow-pea is to the south what clover is to the north and alfalfa to the west. It is an important hay 366 ELEMENTARY STUDIES IN BOTANY crop and soil-renovator in the south, and it is grown to some extent in the north (Fig. 44). It is a bean, rather than a pea, closely related to the ordinary garden bean, and the beans are often used for food. In the south the plant grows as a vine, but it becomes bushy in the north. 73. Suggestions for work. — It is evident that the growth of cereal and forage crops cannot be made a part of the work of the student. Much of this chapter, therefore, must be used as information concerning these very important crops. However, two things should be done, which will form an intro- duction to crop-raising. The first thing is to learn to recog- nize the cereals and forage plants mentioned in this chapter. It is easy to secure samples of the plants and to learn their distinguishing features. The second thing is to germinate and test some of the seeds, so that this very important pre- liminary performance may be learned through experience. Information about a process can never take the place of experience. Information merely suggests how the process may be undertaken, but experience encounters all of the details that are necessary to secure the result. CHAPTER VIII VEGETABLES 74. Definition. — There is no exact definition of the word vegetable. Its application is a matter of usage, including the greatest variety of plant structures. Even the same plant product may be called a vegetable or not ; for example, corn is either a vegetable or a cereal, dependent upon the manner of using it. While the cereals all belong to one great family, the grass family, and all the principal fruits belong to two or three families, vegetables belong to a great number of families. In the following pages representatives of ten families will be presented as being included among vegetables, and these are selected only as samples. Most of the vegetables are cultivated in all countries, but each country is characterized by the emphasis it places upon certain vegetables. For example, sweet corn, sweet potatoes, tomatoes, and watermelons are cultivated more extensively in the United States than anywhere else in the world. These four " vegetables " will serve to illustrate the great variety of structures covered by the name : one is a seed, one is a root, and two are fruits. If to these we add cabbage and lettuce, which are leaves, onions, which are bulbs, and potatoes, which are tubers, we find that at least six different plant struc- tures are included in the term vegetable. 75. Suggestions for work. — In connection with the work of this chapter, not only ought some of the quick-growing vegetables to be cultivated, but as good a collection of vege- tables ought to be brought together as the neighborhood affords. An interesting " field trip " consists in visiting some large market, where the different vegetables can be recog- 367 368 ELEMENTARY STUDIES IN BOTANY nized. It is surprising how many young people there are who can recognize vegetables when served on the table, but who cannot recognize many of them as they appear in the markets. In the following account of some of the more common vege- tables, suggestions as to cultivating them are often included, not because pupils can do such things in connection with this study, but because they should know something of such details, and chiefly with the hope that some of them may be interested in cultivating home gardens. 76. Gardening. — The cultivation of vegetables is usually called gardening, as distinct from farming. A few genera- tions ago almost every family had a home garden, the prod- ucts of which were for family use. In general, this was amateur gardening, and the results were extremely variable. There was no opportunity to select especially favorable soil and climate, for the garden had to be near the home. The general purpose was to secure good quality, a continuous supply, and as great variety as possible. With the growth of large cities a new phase of gardening was developed, known as market-gardening or truck-garden- ing, the products being for sale just as are the products of a factory. This kind of gardening became professional, and the product became very uniform in standard. In establish- ing an industry of this kind, it was possible to select the most favorable soil and climate, sometimes within easy reach of the market, sometimes at great distances from it. The general purpose of a market garden is to secure uniformity, high productiveness, quick growth, and comparatively few crops. 77. Garden soil. — There is a general uniformity in the character of good garden soil, no matter what vegetables are to be cultivated. The soil should be not only rich in the materials for plant food, but also light and loose, which means good drainage. Such a soil is called a " quick " soil because VEGETABLES 369 it enables plants to start early and to develop rapidly. Of course it must be tilled thoroughly and kept so. The plants are also stimulated to rapid and vigorous growth by the free use of suitable fertilizers, the best one being stable manure. Where intensive gardening is practised, many vegetables are started under glass and transplanted as soon as the weather permits (as cabbage, early celery, sweet potatoes, tomatoes, early lettuce), thus securing a much earlier crop. 78. Classification of vegetables. — It would be impossible and unprofitable to enumerate the very numerous vegetables in use. Some of the most common ones must be selected as representatives. Any one who knows how to cultivate these representative forms can extend the same principles to the cultivation of any vegetable. Instead of classifying vegetables by the plant families to which they belong, it will be more useful to classify them by the plant structures they represent. This is more useful because it is the structures that determine the methods of cultivation and not the families. The six structures referred to above will be used: (1) tubers, represented by the potato; (2) roots, represented by the radish, turnip, parsnip, carrot, beet, and sweet potato ; (3) bulbs, represented by the onion ; (4) leaves, represented by cabbage, lettuce, and celery; (5) fruits, represented by the tomato, cucumber, pumpkin, squash, and melons; (6) seeds, represented by peas, beans, and sweet corn. Of course this list probably does not include all of the vegetables cultivated in any locality, but it includes the principal ones. Tubers 79. Potato. — This is the most widely cultivated and valuable of the tubers used as vegetables. The potato tuber is a thickened branch of an underground stem (Fig. 45), and it shows its stem character by its " eyes," which are buds in the axils of minute leaves (scales). America is the native 370 ELEMENTARY STUDIES IN BOTANY home of the potato, the wild plants occurring in the moun- tains and highlands from southern Colorado, through Mexico, and south into Chili. Although potatoes originated in America, they are not so extensively used in the United States as in Europe. For example, in the ten years extending from 1880 to 1890, the average annual crop of the United States was 170 million bushels, while that of Europe was over two billion bushels. In 1912, however, the crop of the United States had be- come 421 million bushels. In 1911 the greatest potato-producing states were Wisconsin (32 mil- lion bushels), Michigan (31 million bushels), New York (28 million bushels), Minnesota (26 million bushels), and Maine (21 million bushels). The potato belongs to the nightshade family (Solanacese), and in its genus (Solanum) occur not only the poisonous nightshades, but also the edible egg-plant ; while some of its associates in the family are tomato, red pepper, belladona, petunia, and tobacco. The flower of the potato plant (Fig. 46) can be recognized by the blue or white corolla, which has five broadly spreading lobes (" wheel-shaped ") ; and its five stamens grouped together about the style, with anthers open- ing by a hole at the top. The fruit produced by the flower is a round green berry. The leaves are pinnately compound, with minute leaflets intermixed with the large ones. The best soil for potatoes is a rich, sandy, well-drained loam, forming a light soil, and this is indicated by the fact FIG. 45. — The potato plant, showing the lower part of the stem, the tubers, and the roots. — After SARGENT. VEGETABLES 371 that those states in which such a sandy soil occurs in abun- dance are the largest producers. Of course potatoes are grown in cold, damp soil, but they are produced more quickly and of better quality in rather dry and sandy soils. Cutting the tubers for planting has been described (p. 326). Each piece should include one or two eyes with as much of the tuber attached as possible, so that there may be abundant food to start the young plants vigorously. FIG. 46. — The potato plant : a, foliage and flowers ; b, single flower ; c, stamen, showing the terminal pores through which the pollen is shed. — After BAILLON. Early potatoes should be planted as soon as the danger of frost is past, for potatoes are sensitive to frost. The cuttings are planted two or three inches deep, in dry and warm soil, and in tilling the ground is kept level until the plants are nearly full grown. Then the rows are " hilled," which makes the soil warmer and drier, and secures an earlier develop- ment of tubers. Late potatoes are planted three or four weeks after the early ones, and somewhat deeper, and there must be frequent level 372 ELEMENTARY STUDIES IN BOTANY tillage to retain the soil moisture during the hot weather when the tubers are maturing. There are hundreds of varieties of potatoes, new ones con- stantly replacing old ones. These new varieties are usually produced under exceptionally favorable conditions, so that in ordinary cultivation they degenerate (" run out "). It is for this reason that many of the most notable varieties of a generation ago have been replaced by new ones. Roots 80. Radish. — This is one of the most popular vegetables, because it grows quickly and is ready for use very early in the season. Since it can be grow^n at any season of the year and develops in so short a time, it is one of the best garden plants for use in school gardens, as well as in home gardens. The radish belongs to the mustard family (Cruciferse) , which con- tains many common wild flowers as well as useful plants. Associated with the radish in the same family are such useful plants as the mustards, water cress, horseradish, cabbage, and turnip. The family is recognized by its four petals (purple and whitish in radish), its six stamens (two of them shorter than the other four), and its pod fruit, which in the radish is at first fleshy and then becomes dry and corky (Fig. 47). The races of radish differ in size, shape, color, and texture, as any one who sees them in market will recognize (Fig. 48). The crop is much more uniform if the seed is sifted to get rid of the small and imperfect seeds and of foreign particles that are apt to occur in any package of seeds. The richer and looser the soil, the better. Spring radishes should be sown as soon as the ground can be worked, for the plants are very hardy, and radishes will be ready for use in three to six weeks. In a week or two later they become pithy, so that repeated sow- ings are necessary for a continuous supply. Summer radishes are of slower growth, and therefore keep longer in condition ; VEGETABLES 373 while winter radishes, whose seeds are sown from the last of July to the middle of September, are still slower in developing, and may be kept in good condition almost as long and as easily as turnips. The planting of the seeds is the same as for many garden crops ; that is, they are sown in rows five to eight inches- B FIG. 47. — A flower of cabbage (mustard family) : A, flower cluster, showing buds- at tip, open flowers below with four spreading petals, and pods at the bottom ; B, a mature pod ; C, a pod opening. — After WARMING. apart, and when the plants appear, so that relative vigor can be recognized, they are thinned so that the individual plants stand about two or three inches apart in each row. 81. Turnip. — The turnip (Fig. 49) is very closely related to the radish, and those who can grow the latter should have no trouble with the former. There are early turnips, 25 374 ELEMENTARY STUDIES IN BOTANY PIG. 48. — Radish. sown as soon as the ground can be worked, for use in the late spring and summer ; and late turnips, sown very late and stored for winter use. In the home garden, the seeds are planted in rows ten to twenty inches apart, and afterwards the plants are thinned to six to ten inches apart in the rows. Turnips are such hardy plants that they require no special care in culti- vation. Turnips, however, are often grown as a field crop, to be raised on a larger scale, either for the market or for feeding. In this case the rows are farther apart (about 30 inches), so that a horse may be used in tilling the soil. It is reported that some- times the yield of turnips reaches 10CO bushels to the acre. 82. Beet. — The beet belongs to a family of homely weeds, known as the goosefoot family (Chenopo- diacese), and about its only useful associate is spinach. The inconspicuous flowers occur in clusters which form a spike ; but the leaves are large and sometimes purple tinged, and are often used for " greens." Young beets form an important early crop of the market gardens, often many acres being employed in their cultivation. The soil needed and the tillage are the same as for other root crops. The first sowing is done as soon as the soil can be worked, and the usual rows (about a foot apart) are established, followed by FIG. 49 —Turnip.— After , i BAILEY. the usual thinning (to about six inches apart). Of course when horse cultivation is desirable, the rows must be farther apart (two to three feet). There is also VEGETABLES 375 a fall crop, for winter storage, the seed for which is sown in June. 83. Sweet potato. — This is a root crop that differs in several particulars from those just described. Sweet potatoes are often mistakenly called tubers. The ordinary potato is a tuber, that is, a thickened underground stem ; but a sweet potato is a thickened root, and is not a tuber any more than radishes, and turnips, and beets are tubers. In these three plants just mentioned, the " vegetable " is the thickened tap-root ; while sweet potatoes are thickened root branches. The sweet potato is a morning-glory, in which genus (Ipomcea) there are many showy cultivated plants. The family is called the convolvulus family (Convolvulacese). The sweet potato plant is a trailing vine whose branches root at the joints (Fig. 50), or it may be cultivated as a bushy plant. The potatoes are borne close together under the crown of the plant, that is, just below where the stem merges into the root, or where the joints " strike root." Since sweet potato is a morning-glory, there should be no difficulty in recognizing its conspicuous funnel- shaped, purple flow- ers (Fig. 50). The leaves are quite variable, having a general triangular outline, and often i FIG. 50. — Sweet potato. heart-shaped at base. Sweet potatoes are more extensively cultivated in the United States than in any other country, the annual yield being about 50 million bushels. They need a warm, sunny climate, a long growing season, loose, warm soil, and plenty of moisture. These conditions are found in our southern states, and therefore sweet potatoes as a commercial crop are 376 ELEMENTARY STUDIES IN BOTANY grown almost exclusively in the southern states, from Vir- ginia around to Texas. The most northern state in which they are grown on a large scale is New Jersey; and fairly large crops are pro- duced in Ohio, Indiana, Illinois, and California. Propagation is by means of sprouts that develop from the potatoes when they are planted in propagating beds or frames. These root sprouts are used as slips or cuttings. Sometimes cuttings are also obtained from the tips of fresh runners. The plant is very sensitive to frost, and there is often great loss on account of planting too early. The sprouts are set in r°WS ab°Ut f°UI> feet aai>t the kntS in FIG. 51.-Sweet potato, showing the charac- each row being about 18 inches apart. ter of flower and leaf . . . A good average yield is said to range from 200 to 400 bushels an acre, and the crop is harvested immediately after the first frost. Sweet potatoes are often raised in the northern states on a small scale as a home garden crop. In this case, loose- ness and warmth of soil are secured by planting the slips on ridges of soil. 84. Parsnip and carrot. — These vegetables are the thickened tap-roots (Fig. 52) of two plants belonging to the parsley family (Umbellif erse) . They are introduced here not so much on account of their importance, as to illustrate root crops from another family of plants. The family is a large one, including, along with parsnip and carrot, such well- known forms as coriander, fennel, caraway, hemlock, and FIG. 52. — Carrot. VEGETABLES 377 celery; in other words, vegetables, aromatic plants, and poisonous plants. The family receives its name from its characteristic flower-cluster (umbel), which is flat-topped, the individual small flowers or groups of flowers standing on branches (rays) that arise from a common point and spread like the rays of an umbrella. Wild carrot, with its umbels of small white flowers, is one of our bad weeds; while wild parsnip, with its umbels of small yellow flowers, is very common. The cultivation of parsnips and carrots is in general the same as for such root crops as turnips and beets, but they are slow-growing plants and it is a long time between the sowing and the harvest. Bulbs 85. Onion. — The best-known edible bulb is the onion, probably a native of western Asia and brought into cultiva- tion in very ancient times. Onions, leeks, and garlic belong to one genus (Alliuni), which is a member of the lily family (Liliacea3). Among their associates in the family are such ornamental plants as the lilies, tulips, and hyacinths, and the well-known vegetable, asparagus. The necessary soil is the usual good garden soil, and thorough cultivation is required. Onions are very hardy, and in the northern states the seeds are sown or the bulbs planted as soon as the ground can be prepared properly in the spring ; in fact, it is common to get a good start by preparing the ground in the fall. The seeds are small and do not germinate quickly, and great care has to be taken to keep the beds free from weeds, as onions cannot stand such competition. The seeds are sown thickly in rows, and afterwards the young plants are thinned out so as to be properly spaced. It is more common to propagate onions by " sets," espe- cially for early onions, and sets are of three kinds : (1) " top 378 ELEMENTARY STUDIES IN BOTANY onions/' which mean the bulblets that appear in the flower- clusters; (2) " multipliers " or " potato onions/' which mean the separate parts or cores in which a bulb often develops ; and (3) ordinary bulbs arrested in growth, sometimes called 11 stunts." The top onions quickly produce young bulbs, and these are the " young onions " that appear in market. The stunted bulbs are produced from seeds, by sowing very thickly in rather poor soil. In such conditions the bulbs soon reach their limit of growth and are harvested, kept over winter, and planted in more favorable conditions the next spring. Leaves 86. Cabbage. — This plant has been very long in cultiva- tion, and grows wild on the sea-cliffs of western and southern Europe (Fig. 53). From this wild plant, such different- looking forms, as the various cabbages, cauliflower, Brussels sprouts, etc., have been derived (Figs. 54-60). It belongs to the mustard family (Crucifera?), and its well-known associates are enumerated in the account of the radish (p. 372). Cabbages can grow in almost any kind of soil, but they must have plenty of food and water, though not an oversupply of the latter. Hot and dry air does not prevent growth, but it does pre- vent the formation of "heads," which are merely large buds. For this reason, heads do not form well in the summer weather of the United States, and hence in the north seed-sowing is timed to avoid "heading" in hot weather, while in the south the plants are grown during the winter and spring months. FIG. 53. — The wild cabbage growing on a cliff. — After BAILEY. 66 379 380 ELEMENTARY STUDIES IN BOTANY The earliest varieties develop in about three months from seed, and the later varieties extend this period up to six or seven months. The seeds are sown in boxes in the usual rows, and then transplanted into the permanent bed. If they are to be set out in March, the seed is started early in Feb- ruary. For later crops the seed is sown out of doors in a well- prepared germination bed, which is repeatedly raked to hold moisture until the plants are removed to their permanent place. 87. Lettuce. — This is the most popular salad vegetable and grows so quickly that it should be one of the forms used in school work. It belongs to the largest family of flowering plants (Composite), a family which is also the highest in rank, which means that it is regarded as the most highly organized family in the plant kingdom. Some of the familiar associates of lettuce in this great family are such ornamental plants as golden-rods, asters, daisies, sunflowers, dahlias, and chrysanthemums ; such weeds as ragweed, cocklebur, thistle, and dandelion; and such useful plants as chicory and artichoke. The family is characterized by its compact head of flowers, which is thought of by most persons as a single flower (Fig. 61). But if the so-called flower of dandelion or sunflower be examined, it will be discovered that it consists of numerous very small flowers packed together upon a flat disk (receptacle) , and the whole assemblage of flowers surrounded by a rosette of small leaves (involucre) . There are two general types of lettuce in cultivation : (1) head lettuce, which heads up like cabbage, and (2) loose lettuce. The latter is more used because it is grown more easily, but the former is regarded as the finer. Since the value of lettuce depends upon its freshness, it is grown almost universally in home gardens, and a very small area yields enough to supply a family. There is no vegetable grown so easily in sufficient quantity in city backyards. The proper VEGETABLES 381 FIG. 61. — The head (so-called "flower") of a composite (Arnica) : A, a plant showing an open head ; B, one of the flowers that make up the margin of the head ; C, one of the flowers that make up the center (disk) of the head. — After HOFFMAN. thing is to secure as long a succession of fresh lettuce as pos- sible. In early spring, about when the grass is starting, a suitable area should be spread with fine manure, and then the soil pulverized and smoothed over. A furrow about an inch 382 ELEMENTARY STUDIES IN BOTANY deep is marked in the fine soil, the seeds are dropped in (twenty-five to fifty in a foot), and then covered with fine and pressed-down soil. In fifteen to twenty days the plants are thinned out, leaving eight to ten in a foot ; and at the same time a second row is planted. About twenty days later the first row is thinned again, so that the plants are six to twelve inches apart (according to size) ; the second now re- ceives its first thinning ; and a third row is started. Even a fourth row may be started, but it is not likely to do very well on account of the hot weather. For market purposes, the plants are started in the green- house in February, and planted out of doors as soon as the weather will permit. A large industry has developed, also, in forcing lettuce under glass at all times of the year, so that fresh lettuce can always be obtained. 88. Celery. — Celery is cultivated for the leaf stalks (petioles), which are blanched and made tender. It is poorly grown if it is greenish and tough. Celery belongs to the parsley family (Umbelliferse) , and its well-known asso- ciates were enumerated in connection with the account of parsnips and carrots (p. 376). This vegetable is in such extensive use and requires such special treatment that it has come to be cultivated as a field crop rather than as a home garden crop. For its best develop- ment it requires a special soil, really a bog soil, but it can be grown well on clay or even sandy soils if they are enriched and irrigated. Although this is a market garden crop rather than a home garden crop, the use of celery is so universal that some information as to its culture seems desirable. The seeds are sown in special frames of various kinds, and germination is a slow process, the seedlings being ready to transplant in about three months. For the early crop in the northern states, therefore, the seeds are started in January; and for the late crop they are started in March. The seeds are broadcast, and the young seedlings are transplanted to VEGETABLES 383 other frames and spaced two to three inches apart. As soon as a new set of roots and leaves are put out, the plants are set out in the field about six inches apart in rows three to four feet apart. For blanching the early plants boards are used, which are set up on edge beside the rows, brought together at the top, and held by cleats. Late celery is blanched by banking the earth against the plants, the banking being heightened two or three times. Another common vegetable cultivated for its petioles is rhubarb, which belongs to the buckwheat family (Poly- gonaceae), and has various " docks " for its near relatives. Fruit 89. Tomato. — The tomato is a native of tropical America, and this at once suggests that it is sensitive to frost and needs warm and sunny soil and a long season. The fruit, which we use as a vegetable, is really a berry, like currants and goose- berries. The fruit was once called " love-apple " and was thought to be poisonous, but now it is very extensively culti- vated, and in North America, where it is grown more exten- sively than in any other country, it has reached its highest degree of perfection in desirable varieties. In the United States it is grown more extensively for canning than any other vegetable, a recent report stating that over 130 million cans are packed each year, representing the cultivation of 300,000 acres. The leading states in tomato-production for canning purposes are Maryland, New Jersey, Indiana, and California. Tomato is a member of the nightshade family (Solanaceae), and its familiar associates are enumerated in connection with the account of the potato (p. 370). Since the plants are very sensitive to frost, they are started in hotbeds and transplanted as soon as the danger of frost has passed. The plants are set four to five feet apart each way, and in garden-cultivation they are usually " trained " to keep 384 ELEMENTARY STUDIES IN BOTANY the fruit off the ground, thus securing more rapid ripening and larger and better-colored fruit. The best method of training is to support a single stem by a stake, but this is troublesome when many plants are grown. The same general results may be secured by allowing the plants to grow over an inclined rack or trellis. 90. The gourd family. — This is a notable family (Cucur- bitacea?) for containing numerous useful forms, whose fruits are used either as fruits or vegetables, but usage has included them all among vegetables. One genus furnishes the cucum- ber and muskmelon ; another the watermelon ; and a third the pumpkin and squash. They are all tendril-bearing herbs, with large, more or less lobed leaves, and rather large axillary flowers, which are usually yellow. The flowers are of two kinds, one (staminate) bearing the three stamens, the other (pistillate) bearing the pistil. In pumpkin, squash, and watermelon, both kinds of flowers are solitary in the axils ; while in cucumber and muskmelon the staminate flowers are in clusters. All of these forms thrive best in good soil, such as is suitable for corn and wheat ; they are all sensitive to frost ; and the seeds of all are planted in " hills." This method of planting is distinct from " drills " or rows, meaning the dropping of four to six (or more) seeds in a single pocket of soil, the groups of seeds being four to six feet (or even eight to ten feet) apart each way. It is also very customary to put some well- rotted manure in each hill, thus forcing the young plants into vigorous and continuous growth. Cucumber. — The cucumber is a native of southern Asia, and has therefore been long in cultivation. It is grown both as a field crop and a garden crop, and seeds can be sown in the open as soon as danger of frost has passed, and the crop develops during the warm months. Muskmelon. — This plant is a native of the warmer parts of Asia. This means that it is a tender plant, and an early VEGETABLES 385 start in the northern states must be secured by starting seeds in hotbeds ; but in the southern states they may be sown in the open field. There are two general types of muskmelon cultivated : (1) those with furrowed and thick rind, called " canteloupes " ; and (2) those with netted and softer rind, called " nutmeg melons." Two notable races of nutmeg mel- ons are the "Osage melon," developed in Michigan, and the " Rocky Ford melon," developed in Colorado. The canteloupe melons have a longer season, but the nutmeg melons are most commonly grown in the northern states in home gardens and for the early market. New Jersey is said to supply one-half the muskmelon crop ; and the southern states cultivate muskmelons only for the local markets. Watermelon. — The watermelon is a native of tropical Africa and has been very long in cultivation, but the United States now produces a larger crop than any country in the world. The watermelon develops to the greatest perfection in the soil and climate of the southern states, Georgia being particularly noted for producing the bulk of the crop shipped to the northern states and also the choicest melons. Of course in the southern states watermelons are grown as a field crop, but they can be grown readily in home gardens. The soil must be such that the plants can start quickly and grow rapidly. Pumpkin and squash. — These coarse trailing vines grow best in corn land, and are often grown in cornfields, being planted along with the corn. Seeds 91. The legumes. — Peas and beans are the chief represen- tatives of the legume family (Leguminosae) whose seeds are used as vegetables. Other familiar representatives of this family are enumerated in the account of forage plants (p. 362. It is evident that since peas and beans are legumes they do not impoverish soil, so far as its nitrates are concerned, but 386 ELEMENTARY STUDIES IN BOTANY can obtain their own nitrates with the help of soil bacteria ; but this does not mean that they can do well on poor soil. Peas. — The cultivation of peas is extremely old, the plant being a native of southern Europe and Asia, and used exten- sively by the most ancient races. There are numerous varieties of garden peas and field peas, but there are two types of garden peas that can be recognized easily : (1) those with smooth seeds, which are earlier and hardier varieties; and (2) those with wrinkled seeds, which are of better quality. Many of the garden varieties need poles six to eight feet high ; others are not such high climbers ; while still others are dwarfs and do not need stakes. The method of planting and cultivating is the same as for beans, and will be described in the next paragraph. Beans. — There are many kinds of beans, but the ordinary beans cultivated in this country are probably natives of trop- ical America. The two types in ordinary cultivation are the bush beans, which are field beans, and the pole beans, which are garden beans, the latter demanding more fertile soil than the former, especially the best of all the pole beans, the Lima bean. In the cultivation of field beans, the seeds are usually planted in rows two to three feet apart, with the plants three to six inches apart in each row, and the soil is kept well stirred between the rows. In the case of pole beans, the poles are set about four feet apart each way and four or five beans planted around each pole, and the soil is cultivated frequently. Sweet corn is also a notable seed-vegetable, which has been presented in connection with the cereals (p. 350). CHAPTER IX FRUITS 92. The families. — The majority of our cultivated fruits belong to the rose family (Rosacese), whose name suggests the general character of its flowers, with their more or less showy petals and numerous stamens (Fig. 62). One divi- sion of the family includes in a single genus (Prunus) peaches, apricots, plums, and cherries, which are " stone fruits " or " drupes." In this kind of fruit the outer part of the ovary becomes fleshy and the inner part stony, the seed being the kernel within the stone (" pit ") (Fig. 63). In the case of the almond, the outer layer ripens dry instead of fleshy and splits off, freeing the large and softish stone, whose kernel (the seed) is eaten. Another division of the family includes in a single genus (Pyrus) apples, pears, and quinces, whose fruits are " pomes." In this case the flesh consists of the thickened calyx tube which becomes consolidated with the ovary (" core ") (Fig. 64). The edible part of the fruit, therefore, is the calyx tube, while in stone fruits it is the ovary wall. The third and largest division of the family, to which the roses themselves belong, includes strawberries, raspberries, and blackberries. The strawberry is really a fleshy recep- tacle on which numerous minute pistils (the " pits ") are borne (Fig. 65) ; wh'ile raspberries and blackberries are clus- ters of small fruits resembling minute stone fruits. In the raspberry the cluster of fruits slips from the receptacle like a cap (Fig. 66) ; while in the blackberry the cluster and the receptacle become fleshy together. 387 388 ELEMENTARY STUDIES IN BOTANY A second important fruit-bearing family is the rue family (Rutacea), whose genus Citrus includes oranges, lemons, and grape-fruits. The genus is a native of Asia, but these fruits are known everywhere. From the name of the genus, this group of fruits is usually called the " citrous fruits." FIG. 62. — Pear, showing a branch with flowers (A), a section of the flower, showing, how the calyx and ovary grow together to form the fruit (B), and a section of the fruit (C), showing the thickened calyx outside and the ovary or "core" within (indi- cated by the dotted outline). — After WOSSIDLO. These are all really berries with a leathery rind, a berry being an ovary that becomes pulpy throughout (as currants, gooseberries, grapes, tomatoes). A third notable fruit-bearing family is the vine family (Vitaceffi), for it includes the grapes. The habit of these woody climbers, with their tendrils, broad leaves, and clus- teis of small but fragrant flowers, is probably familiar to all, FRUITS 389 for more kinds of grapes, both wild and cultivated, grow in North America than in any other country. 93. Classification. — The most useful classification of these fruits, for it groups them according to methods of cul- ture, is as follows : (1) orchard or tree fruits, which are sub- divided into pome fruits (apple, pear, quince), stone fruits (peach, plum, cherry), and citrous fruits (orange, lemon, grape-fruit) ; (2) vine fruits (grape) ; and (3) small fruits (strawberries, raspberries, blackberries, currants, and goose- berries). Orchard Fruits 94. Orchards. — The cultivation of orchard fruits is prob- ably most highly developed in North America. A genera- tion ago an orchard in connection with a home was the usual thing ; but now great areas are under cultivation by professional fruit-growers. In the old home orchard the trees were left to take care of themselves, so that the fruit crops were uncertain and variable, dependent upon the accident of soil and climate. Now great care is given to the soil and to the trees, and the result has been great increase in productiveness, greater uni- formity, and finer quality. In establishing an orchard the soil is prepared as thoroughly as for any other crop, and for two or three years deep . . FIG. 63. — Section of a ploughing is practised. This puts the peach, showing PuiP and • i . j r • i TJ- £ stone formed as two SOll in gOOd physical Condition for re- layers of the ovary wall, taining water, makes the soil salts more available, and assists the young trees in establishing a sufficiently extensive root system. After- wards there is frequent light tillage early in the season ; then often a cover-crop (such as clover) is sown, which is left all winter and is ploughed under in the spring. 26 390 ELEMENTARY STUDIES IN BOTANY Pruning has also come to be a fine art, and when done properly, a little every year, there is a larger yield ; and when to this there is ad'ded an intelligent thinning of the develop- ing fruit, the quality is improved. 95. Apple. — The apple is the most important pome fruit, having been cultivated from very ancient times. It is a native of southwestern Asia and adjacent Europe, but is now under cultivation in all countries. All of the differ- ent kinds of apples, which number about 1000 on sale in ; * FIG. 64. — Longitudinal and cross-sections of apple, showing the "five-celled" ovary (core) imbedded in the fleshy cup of the calyx. any year, have been derived from two wild species, one of which has given rise to the ordinary apples, the other to the crab apples. The enormous number of varieties makes it possible to select for each area those best adapted for it, and this information is perhaps best obtained from the various state horticultural societies. In the United States and Canada there are several notable areas of apple cultivation, and new ones are being developed rapidly. What has long been regarded as the finest apple region in productiveness, quality, and good keeping is the region extending from the Great Lakes eastward to Nova FRUITS 391 FIG. 65. — A straw- berry, being an en- larged and pulpy receptacle bearing numerous seed-like fruits sunken in small pits. — After BAILEY. Scotia. Other notable regions are in Virginia, in Arkansas, in various parts of the plains, and in the Pacific states. More apples are produced in North America than in any country of the world, a good crop for the United States and Canada being approximately 100,000,000 barrels. One of the reasons why the proper care of apple orchards has been so much neg- lected is that they thrive reasonably well almost anywhere. The best land, however, is said to be good wheat or corn land, which means a clay loam. The grafting methods by which old stocks may be used to sup- port more desirable varieties have been described (p. 330). 96. Pear. — The pear is also a native of Asia and Europe, but is a much more un- certain crop than the apple. It flourishes best from the New England states to the Great Lakes, and on the Pacific slope. In the interior, the uncertainty of the pear crop arises from the prevalence of a disease called " pear blight," which blasts the branches, and which spreads so rapidly that exten- sive orchards may be destroyed. In the south, the climate is too warm for the best development of trees and for the best qual- ity of fruit ; while in the northern prairie states the winters are too severe. There are many varieties, but those most common in the markets are very apt to be the various races of Bartlett, Kieffer, and Seckel pears. The pear can be grafted on FIG. 66. — A raspberry, showing the "cap" of small fruits removed from the receptacle. — After BAILEY. 392 ELEMENTARY STUDIES IN BOTANY quince stock and grown as a dwarf. These " dwarf pears " reach the bearing stage earlier than the others and are more easily handled in all the necessary operations, but they require more care than do the ordinary trees. The quince needs no special statement. It is an interest- ing and peculiar fruit, but there is no large or increasing demand for it. 97. Peach. — The peach is probably the most highly prized of the stone fruits. A native of Asia, its cultivation in the United States is always attended with risk. This arises from the fact that it is a very early bloomer, and being sen- sitive to frost, the flowers and buds are in danger of being killed by a late frost. This risk is greater in the south tnan in the north, because the buds swell earlier. On account of this danger from freezing, the commercial areas of peach cultivation are near large bodies of water, where the winter temperature is milder, as near the sea- coast, far enough inland to escape strong winds, and near the Great Lakes. Of course peaches are grown over a great range of country, the failures probably being as frequent as the successes, but the commercial regions are not numerous. The peach orchards along the southern borders of the Great Lakes extend along Lake Ontario in New York and Canada, along Lake Erie in Ohio, and along the eastern shore of Lake Michigan. It is in the " Michigan fruit belt " that the peach reaches its northern limit in the eastern states. Another large area extends from Connecticut, near Long Island Sound, southward to Cape Charles (Virginia), the " Delaware peaches " holding the same important position in the eastern market that the " Michigan peaches " do in the western. Other peach areas are in northern Georgia and Alabama and adjacent states; from southern Illinois westward into Kansas ; in western Colorado ; and throughout California, except in the mountains. FRUITS 393 As may be inferred from the regions of most successful peach-cultivation, a light and sandy soil is the best, being quite in contrast with the best soil for pome fruits. Peaches are propagated by seeds, and then on the seedlings of the first year the desired varieties are budded. The tilling and other care of a peach orchard can never be neglected. 98. Plum. — There are native plums in all countries, and numerous species are in cultivation. Since they are so variable in origin, they are not equally adapted to all regions. The European type is the plum of history and is cultivated in the northeastern states and on the Pacific slope. It has produced the more familiar old races, such as the Green Gage, Damson, etc., and is the chief source of prunes. In the same regions, and also in parts of the interior and in the south, the Japanese plums are gaining recognition. In the colder northern regions and over the larger part of the in- terior basin our own native plums are cultivated. There are hundreds of varieties, no less than 300 varieties having been derived from six native American species. In propagation, grafting and budding are practised as usual ; but to secure desirable varieties not adapted to the soil conditions of a region, it is customary to grow stock plants for soil conditions and graft scions upon them for the fruit. Prunes are plums that dry sweet without removing the pits. In other plums there is a fermentation or " souring " about the pit as the plum dries. In California, prunes form the most important plum product, 6,000,000 trees (55,000 acres) being reported in 1900, seven-eighths of which were used for prune-production. 99. Apricot. — This fruit, intermediate between peach and plum, is a native of the China-Japan region, and is grown commercially in New York and other eastern states, and also in California. Its importance in California may be indicated by the fact that in 1900 there were 3,000,000 394 ELEMENTARY STUDIES IN BOTANY trees (40,000 acres) in cultivation, and the acreage was rapidly increasing. The clanger from frost is the same as for peaches, but the interior valleys of California furnish a most congenial situation. 100. Cherry. — The cherry is of European origin, and the various cultivated races are grouped as sour cherries and sweet cherries. The sour cherries are cultivated in orchards for canning purposes in a number of states, extending from New York and New Jersey to Kansas and Nebraska. The sweet cherries are restricted mostly to what is called " door- yard " planting. In California, cherries are the least com- mercially important of the temperate fruits, but they attain unusual size. Cherry trees are grafted with unusual readi- ness, so that large orchards can be transformed into more desirable varieties. 101. Orange. — This is the best known of the table citrous fruits, and is one of the oldest of cultivated fruits. In fact, it has been so long in cultivation that its native region is in doubt, although probably it has come from southern and eastern Asia. Now it is grown in all warm temperate and tropical countries. The structure of an orange is familiar to every one, but certain variations should be noted. Ordinarily an orange contains ten compartments, but the number is often in- creased through cultivation ; and in some cases a secondary axis with its small compartments is developed in the center of the fruit, forming the " navel " orange. The best-known navel orange is the " Washington navel," which started as a chance seedling brought from Brazil in 1870. This navel orange is also seedless. There are three well-developed orange regions in the United States : (1) central and southern Florida, (2) the delta region of the Mississippi, and (3) California. Formerly most of our oranges were imported from the Mediterranean region, but these were replaced for the most part by Florida FRUITS 395 oranges. In the winter of 1894-1895, however, there occurred the " great freeze " in Florida, and since that time Cali- fornia oranges have become better known. Some apprecia- tion of the destruction wrought by the great freeze may be obtained from the statement that in the season of the freeze the orange crop of Florida had reached its maximum, 6,000,000 boxes, while in the next year there were only 100,000 boxes ; in 1900 the crop reached 1,000,000 boxes. In California, in 1900, there were 3,500,000 trees in cultivation (nearly one- half of them bearing), which yielded 4,000,000 boxes or more. In 1911 the citrous crop of California reached a total of 14,000,000 boxes. 102. Lemon. — This is one of our most important com- mercial fruits, and is cultivated extensively in all tropical and subtropical regions, being less hardy than the orange. In our country, lemon culture is practically restricted to Florida and California, and large quantities of lemons are imported, chiefly from Italy and Sicily. Lemon culture in Florida was almost annihilated by the cold winter of 1894- 1895, when nearly all the trees were killed, leaving only a few isolated orchards which recovered. Since that time, more attention has been given to other fruits. In California, although the lemon has been grown for a long time, its commercial importance has increased only in comparatively recent times. In 1900 there were 250,000 bearing trees and a million more in cultivation. The prominence of California lemons has come from the fact that the old thick-skinned, bitter, and rather juiceless type has been replaced by types having the thin rind, freedom from bitterness, and abundance of citric acid characteristic of the lemons of the Mediterranean region. 103. Grape-fruit. — This citrous fruit has come into great prominence, and there have been many misconceptions as to its origin. It is a native of the Malayan and Polynesian Islands and its real name is " pomelo," a name which means 396 ELEMENTARY STUDIES IN BOTANY literally " melon apple." When it came into cultivation in Jamaica it was called " grape-fruit " because the fruit is borne in clusters of three to fifteen, like a cluster of huge grapes. It has also been called " fruit of Paradise " and " forbidden fruit/' and the pear-shaped varieties, which now seldom appear in market, are called " shaddocks." Grape-fruits are cultivated extensively in India, the West Indies, Florida, and California, but most of the cultivated varieties have been developed in Florida, where it is grown to greatest perfection. Its commercial cultivation extended from Florida to Jamaica and California. The grape-fruit is cultivated like the orange, but it is more sensitive to cold, and in the destructive winter of 1894-1895 all the trees were killed in northern and central Florida. Vine Fruits 104. Grape. — The grape is probably the oldest fruit in cultivation, and its chief use has been the manufacture of wine. The grape of history is Vitis vinifera (the specific name means " wine-bearing "), and it is probably of Asiatic origin. Although the chief use of grapes is to manufacture wine, a secondary use is the production of raisins, and in the United States there has been developed a notable series of " table grapes." The grape in this country has had a most interesting his- tory. The early settlers naturally tried to introduce the European Vitis vinifera, but after persistent effort its cul- tivation had to be abandoned on account of a destructive disease that attacked it. Then attention was given to the possibilities of the native American grapes, of which there are numerous species. A species of the Atlantic coast region (Vitis Labrusca) has been most developed, and its cultivated varieties were produced to eat rather than to drink. Among them are such well-known grapes as the Concord and Catawba. The United States is responsible, FRUITS 397 therefore, for the development of the highest types of table grapes. In addition to the native species that have been brought under cultivation, from which 800 named varieties have been produced, there are numerous other promising species that await development. While table grapes were being developed in the eastern states, the Old .World Vitis vimfera was being established in California, where it was free from the disease which attacked it in the eastern spates. In California, therefore, grape culture is like that in Europe, and wine is the principal product. Although grapes are cultivated almost everywhere in the United States, the area of commercial grape culture is not very extensive. The greatest areas in the eastern states are those in New York and Ohio bordering lakes and large streams, as the lower part of the Hudson River valley, the lake region of central and western New York, and the Lake Erie region of New York, Pennsylvania, and Ohio. There are also large vineyards in Ontario, Michigan, etc., and grape culture is extending into other regions. The area of grape culture in California in 1900 was 140,000 acres, one-seventh of the product being table grapes, two-sevenths raisin grapes, and four-sevenths wine grapes. The care of grape-vines requires knowledge and experi- ence, for proper pruning, to reduce the amount of wood and to keep the plant in suitable form, can be learned only by demonstration. The training of the vines is to keep them off the ground, so that the fruit may be exposed to light and air. Naturally in extensive cultivation this training is of the simplest sort to secure the result ; but in home cultiva- tion it often takes the form of a more or less elaborate " grape arbor." The propagation of grapes is usually by cuttings, already described (p. 326), which are usually secured in the winter from the trimmings of vineyards. These cuttings, each one with two or three buds, are usually kept until spring by being buried half their depth in sand in a cellar. 398 ELEMENTARY STUDIES IN BOTANY Small Fruits 105. Strawberry. — There are wild strawberries in the eastern states, and a generation or two ago strawberries were scarcely known except in the wild state, but these wild species have not yielded much to .cultivation. All of the common cultivated forms are derived from a Pacific coast species which was introduced into cultivation over 200 years ago from Chili. It is now possible for any one who has a plot of ground to have a strawberry bed. The strawberry plant is propagated naturally by runners, which form after blossoming. A runner strikes root at the FIG. 67. — A strawberry plant, showing a runner that has de- veloped a new plant, which in turn has sent out another runner. — After SEUBERT. tip and sends up a cluster of leaves, thus establishing an inde- pendent plant (Fig. 67). In cultivation, these runner plants are transplanted or let alone, and they bear fruit the follow- ing year. A strawberry bed may bear for several years, but the first and second crops are the best, so that it is cus- tomary to break up a bed after one to three years of bearing. The best soil is a dark, sandy, and rather moist loam, and good drainage is necessary. In preparing a bed the soil is top-dressed with fine manure and well pulverized. Then the plants are set out, obtained from the runner plants of the previous season. These young plants are usually better allowed to remain in connection wTith the parent plants until FRUITS 399 spring and then transplanted, and of course runner plants that have not borne fruit are the best. To secure the best berries, each plant should have a space to itself (" hill "), which can be cultivated all around. The old way of allow- ing beds to become matted with runners is passing out, for many berries are covered up and in a very unfavorable posi- tion for development. Therefore, when a large area is under cultivation, and liberal hills are impracticable, narrow and rather close rows are used, so that as much fruit as possible may be "on the outside." In the fall it is usual to mulch the beds to protect them through the winter and early spring. This mulch is a covering of clean straw or material containing straw. In the south, pine needles are used, while near the sea-coast salt marsh hay is convenient. The growth of strawberry plants is during the cool season of the year, and of course in the south this means very early in the year. In fact the cultivated berries seem to find their most congenial home in the south, where they are the most important of the small fruits. 106. Raspberry. — Raspberries are brambles, associated in the same genus (Rubus) with blackberries, from which they differ in the fact that the close cluster of small fruits separates from the receptacle like a cap. The European species (Rubus Idceus) has been longest in cultivation, and has yielded many important varieties of high quality, but it lacks hardiness and productiveness in the United States, and for this reason it is our least important species. It is from American species that we have obtained our commonly cultivated red and black raspberries. Rubus strigosus is a red raspberry, like its European relative. Per- haps it is inferior in quality, but it is more hardy and pro- ductive, and therefore almost all the red raspberries of the market are from this American species. Rubus occidentalis is the black raspberry, or " black cap," and its races, although they are perhaps less liked by most people than the reds, are 400 ELEMENTARY STUDIES IN BOTANY our most important commercial raspberries, for they are easily cultivated, are hardy and productive, and are better for market handling. The black raspberries are propagated by cuttings obtained by layering, a process already described (p. 329) ; while red raspberries develop numerous suckers from the roots which are often used as cuttings. 107. Currant and gooseberry. — These are two of our hardiest bush fruits, that are propagated by cuttings, layer- ing, and root cuttings. They are more intensively culti- vated in England than in the United States, the English gooseberries being highly cultivated and used as a table fruit in a way that is impossible with their American relatives. 108. Suggestions for work. — The fruits mentioned in this chapter are in such common use and so easily recognized that there is no need for exercises in distinguishing them, but there are four useful things that should be done if possible. 1. The various fruits should be sectioned and their struc- ture examined, noting the variations that occur, especially in the amount of fruit pulp. 2. The home markets should be visited and inquiries made as to the sources of the fruit displayed. This will develop some knowledge of the regions from which various fruits come at different seasons, and will also fix the seasons when the dif- ferent fruits may be expected and when they are at their best. 3. The names of the most common varieties should be learned. For example, the prominent apples and pears should be known by name and recognized at sight. 4. If the neighborhood permits it, orchards, and even dooryards and gardens, should be visited to see the various fruit-bearing plants in cultivation. This will fix in mind the general habit of the plants, their appearance in cultiva- tion, and will probably enable the student to contrast proper and improper methods of cultivation. CHAPTER X FLOWERS 109. Floriculture. — The cultivation of flowers for orna- ment and of ornamental plants is called floriculture. The use of plants for this purpose has brought into cultivation a very large number of species ; in fact, floriculture has drawn upon the whole of the immense group of flowering plants ( Angiosperms) , and has selected for its work whatever is beautiful or curious. It is evident that it will be impossible to give an account of even the most common flowers and ornamental plants in cultivation, but some general idea can be given of the work of floriculture. Plants are in more general cultivation for their flowers than for any other pur- pose. The public parks are full of them, almost every yard has its flower bed, and in the absence of yards " window- gardens " are established. The cultivation of such plants, therefore, touches the experience of more people than any other kind of cultivation; besides, it is just as possible in cities as in the country. Floriculture is not merely the cultivation of ornamental plants by people in general, but it has also developed into an extensive business, conducted by " florists," and the work is done chiefly in greenhouses. The demand for flowers, and especially " cut flowers," has been increasing at such a rate that special equipment for forcing flowers and distribut- ing them has been developed. Naturally the largest estab- lishments are near the large cities, where the demand is greatest, and the cities which are now leading in this busi- ness are New York, Chicago, Boston, and Philadelphia. The greatest amount of greenhouse space used for floricul- 401 402 ELEMENTARY STUDIES IN BOTANY ture is found in New York, Illinois, Pennsylvania, and New Jersey, in the order named. It is reported that about $25,000,000 are expended for flowers each year, about half of it for cut flowers and the other half for plants. The most important commercial flower grown is the rose, the annual sale being at least $6,000,000, which represents about one billion flowers. The second flower in importance is the carnation, the annual sale being about $4,000,000; while the violet is the third. A brief account will be given of the cultivation of a few representative flowers, and they will serve to illustrate the cultivation of flowers in general. 110. Production of new forms. — Great attention is given by florists to the production of new forms of flowers which may attract attention. Every year new forms of roses, carnations, chrysanthemums, etc., are announced. Some of these variations are obtained by detecting a chance varia- tion or " sport " occurring among the ordinary plants. Far the greater number, however, are deliberately worked for by hybridizing (p. 338). Two forms are selected and arti- ficial pollination is secured. The hybrid progeny from the seeds are examined in the hope that one or more individuals may show desirable characters, either new characters or a new combination of characters, and these are propagated. Repeated crosses may be made, several varieties being used and hybrids being crossed again, until often very complex mixtures are obtained. It is evident that by making crosses repeatedly and in every direction, a reasonable number of attractive combinations are obtained. It is like stirring up all sorts of food ingredients in all sorts of proportions, in the hope that some one of the mixtures will prove to be a pala- table dish. While this method of securing new forms seems to be largely a matter of chance, if a sufficiently large number of hybrid forms is produced, the chance of securing a desir- able form becomes a practical certainty. FLOWERS 403 It must not be supposed that miscellaneous mixtures are the only ones used by florists. Often the mixtures are definite and have in view a combination of desirable char- acters that exist separately in the two parents. For example, it is very common to work for such a combination as color and size of flower, by crossing flowers of the desired color with flowers of the desired size. In this way, for example, many new carnations and chrysanthemums are produced. Often it is desired merely to increase the size of a desirable flower beyond its usual limit, and this can usually be secured by the selection and propagation of the largest flowers through a series of generations. This has resulted in the production of some remarkably large chrysanthemums and carnations. One of the best illustrations of crossing to secure definite results is the Shasta daisy produced by Luther Burbank. It is a triple hybrid, that is, it is a mixture of three forms, each one contributing certain features. The American form, common throughout the east as a weed, is known as oxeye daisy or marguerite. It is an abundant bloomer, but the habit of the plant is not handsome, being rather loose and straggling. The English representative has a handsome habit, with tall and stiff stems; while the Japanese form is characterized by the pearly luster of the flowers. By crossing these three forms, the Shasta daisy was produced, which combines in a single individual the profuse blooming of the American form, the erect habit of the English form, and the pearly white flowers of the Japanese form. Ill . Rose. — The varieties of roses (Fig. 68) are so numer- ous and the methods of handling them are so varied that no general account can cover them. The situation may be illustrated, however, by taking the case of a home rose garden, which any one can secure who controls a small plot of ground. The spot selected must be sunny, but protected against 404 ELEMENTARY STUDIES IN BOTANY the worst winds, as by a fence or hedge. As a well-known writer has said, " the rose garden must have shelter, but it must not have shade." The best results are secured with good garden soil, but a rose bed can be made good if the original soil is bad, the chief thing to provide for in such a case being a deep bed and good drainage, for roses do not tolerate free water in the soil. Roses are propagated by seeds, cuttings, grafting, and budding, but those who are preparing a small rose garden will probably use cuttings or started plants obtained from a florist or from a neighbor. These cuttings are best planted late in autumn, about 30 inches apart, and the soil protected, preferably with stable manure. In the spring the bed should receive shallow tillage, and then the surface should be raked at intervals. Cultivated roses are roughly grouped into two kinds : those that bloom only once (in sum- mer) and those that bloom more or less continuously. The varieties are so numerous, how- ever, and differ so much as to hardiness and adaptation to different regions, that advice as to the selection of the proper forms to cultivate must be obtained from those who have had experience. 112. Carnation. — Carnations (Fig. 69) belong to the pink family (Caryophyllacese), and are associated in the same genus (Dianthus) with the old-fashioned and fragrant " pinks " once found in every home garden. The cultivated carnations are derived from a European species (Dianthus Caryophyllus), which has been cultivated from very early times. The name " carnation " was applied to the plant FIG. 68. — A rose. — After BAILEY. FLOWERS 405 on account of its flesh-colored flowers, but the color of the flower in its wild state has been broken up into a great variety of colors in the cultivated races. It may be of interest to know that the old English name for carnation was " gillyflower," a name that appears often in English literature. The older cultivated races of carnations have practically disappeared, and have been replaced .by new ones that flower more or less continuously and are especially adapted for forcing, so that car- nations can be obtained at any season of the year. It is reported that about 500 varieties of carnation have been produced in the United States, where the carnation industry is better developed than in any other country. Of course carnations can be grown from the seed, but florists use this method only when they are desirous of securing varia- tions that may be useful. In general, they are propagated by cuttings, which may seem strange for an herb. Carnations are not very suitable for ordinary garden cul- tivation, but no one will regret the culti- vation of a few " pinks " with their clove-like fragrance. 113. Violet. — It has been stated that violet culture is third in commercial importance among cultivated flowers. The numerous commercial violets are derived from the European Viola odorata, and their successful cultivation re- quires an amount of intelligent care that can be given only by the specialist. If the violets of the florists are not suitable for home cul- ture, another violet, the pansy, is always suitable, for it is very easy to cultivate (Fig. 70). The pansies are derived from another European species, Viola tricolor, the name re- 27 FIG. 69. — A carnation. 406 ELEMENTARY STUDIES IN BOTANY FIG. 70. — Pansies. ferring to the characteristic variegated colors of the flower. The old English name of the pansy is " heart 's-ease," and it has always been a favorite home-garden flower. Numerous garden varieties have been devel- oped, ' that differ as to size of flower, nature of coloring, and arrangement of colors. The highly developed varieties are not apt to continue true in unskilled hands, so that the safest plan is to secure seed from the breeder each year. The plot selected for the culti- vation of pansies should be shel- tered from wind and exposed to the morning sun if possible, and good garden soil will produce the best pansies. For early spring blooming, the seed is sown in August, the bed is cov- ered with strawy manure and kept moist. In about two weeks the plants will ap- pear and the straw is gradually removed. In the next spring the flowers will appear. To secure blooming during the late sum- mer and autumn, seeds can be germinated within doors from February to June, and the young plants set out into the per- manent bed. 114. Sweet pea. — Sweet peas (Fig. 71), as the name suggests, belong to the legume family (Legumiriosse), along with garden peas and beans. The originals of the cultivated varieties came from the Mediterranean region and southern Asia, and the number of shades of color now represented by the 200 varieties is surprising. The supply of seed for the world FIG. 71. — Sweet peas. FLOWERS 407 is produced principally in California, and on this account a large number of new forms have been secured in America. Although the cultivation of fancy strains has been made a matter of competition, the sweet pea is still a home-garden plant and is usually one of the few selected for planting. Garden soil is needed, but it must be remembered that too much enriching will result in a vigorous vine at the expense of flowers. The soil is prepared in the autumn, and the seeds are planted as soon as the frost is out of the ground. The seeds are placed in rows and cov- ered so that a little furrow is left for the retention of moisture. Germination and early growth should be allowed to proceed slowly, and very superficial till- ing should be employed. The usual garden varieties need a firm support of some kind, about six feet high ; but there are bush varieties that require no support; and also low varieties that spread compactly over the ground. 115. Chrysanthemum. — This is not an ordinary home-garden plant (Fig. 72), but it is so familiar a flower and has had such an interesting history that some information in reference to it is not out of place. It belongs to the com- posite family (Compositse), the ranking family of flowering plants, associated with golden-rods, asters, sunflowers, dahlias, dandelions, etc., its so-called flower being a compact head of small flowers surrounded by leafy bracts (involucre), as described under lettuce (p. 380). The cultivated chrysanthemum holds the same con- spicuous position among the cultivated flowers of the orient that the rose holds in the Occident, the original forms growing as natives in China and Japan. There are very many types in cultivation, but those ordinarily exhibited have large and FIG. 72. — A chrysanthe- mum. 408 ELEMENTARY STUDIES IN BOTANY " doubled " flowers of various colors, with the flowers some- times in a compact ball, at other times more loosely disposed. It is said that the chrysanthemum stands fourth in the list of commercial flowers in the United States, although its season is only about six weeks long. 116. Narcissus. — This is a genus of the amaryllis family, which includes some of the most attractive of the very early home-garden flowers. They are known in general as daffo- dils and jonquils, and are familiar to every one. The flowers are charac- terized by having a " crown " aris- ing from the top of the tubular, six-lobed perianth. The daffodils have large yellow flowers, with a crown as long as the lobes of the flower or longer and with a more or less crisped margin (Fig. 73) ; while the jonquils have small yellow and fragrant flowers, with a crown less than half the length of the flower lobes. The " poet's Narcissus," often cultivated and seen at flor- ists, is like the jonquil, except that the fragrant flowers are white and the short crown is edged with pink. These plants are hardy and easily cared for, so that no garden should be without them. They thrive in good soil, and they develop so early that moisture is usually plentiful. About the only caution necessary is to be careful that no manure touches the bulbs. The bulbs are planted, late in summer or early in the autumn, six to eight inches deep and three inches apart, and remain until strong groups are formed. These groups can occupy the same place for a series of years, and early each spring the flowers begin to appear. These narcissus forms are also especially adapted for house plants, FIG. 73. — A daffodil. FLOWERS 409 three or more bulbs being set in a pot, with the necks of the bulbs at the surface of the soil. A succession of plantings in pots will yield a succession of flowers throughout the winter. 117. Tulip. — The tulips are natives of the oriental coun- tries and belong to the lily family (Liliaceae). The origin of the common garden tulips (Fig. 74) is unknown, for they had been long under cultivation by the Turks before they came under the observation of other nations. The tulip has a curious connection with the history of Holland, for its introduction into that country resulted in the so-called " tulip- craze" of the seventeenth century, a craze which compelled the interference of the government. Holland is still the center of the development of tulip bulbs. The tulips, like the daffodils and jon- quils, are early bloomers, and adapted to cultivation in home gardens. The bulbs are set out in the autumn, before severe freezing, in sandy loam which is best en- riched by leaf -mould and well drained. The bulbs are planted about four inches deep and four to five inches apart, and when the ground begins to freeze the bed should be covered with leaves or other light material. In the spring, when severe cold is over, the beds are uncovered, and the plants will probably require no further attention. In the selection of bulbs, it should be known that the size of the bulb is not so important as an abundance of fibrous roots. 118. Aster. — Asters are introduced here because they are late bloomers, and belong to the end of the season, as tulips, daffodils, and jonquils belong to the beginning of the season. Asters belong to the composite family, along with the chrysanthemum, and they are especially abundant as FIG. 74. — A tulip. 410 ELEMENTARY STUDIES IN BOTANY native plants in North America. The commonly cultivated aster (Fig. 75), however, is not an aster, but is a near relative, whose fuller name is " China aster." As the name suggests, it is a native of China, and is perhaps the favorite fall- blooming flower. It has been developed into " double " forms of various kinds, such as the chrysanthemum, and its original blue has been extended into a series of colors, in- cluding red, pink, and purple. The seeds are sown early in spring, in a well-tilled bed, in shallow rows and covered with fine dirt. When the plants appear, they are thinned out as necessary, and the soil is cared for by the usual tilling to retain moisture in dry weather. A bed of fall- blooming asters in the late autumn, when all other flow- ers are gone, well repays the little care it involves. 119. Suggestions for work. - The very few flowers de- scribed in this chapter are intended to be only samples of the more commonly seen flowers, and the list should be much extended by observing the various flowers in common cultivation in the neighborhood, both in home gardens, and by florists. A visit to some florist's establishment will give some idea of the kinds of flowers that are being cultivated for the market at a given time. In addition to these observations of flowers in cultivation, some of the more rapidly growing forms should be propa- gated as a part of the laboratory work, and other represen- tative forms should be brought from the florist's in pots, and not only observed, but also cared for. FIG. 75. — China asters. — • After BAILEY. CHAPTER XI FIBER PLANTS 120. General statement. — While fiber plants cannot be included among those of common cultivation, they cannot be excluded from any account of important plants culti- vated by man. Moreover, some of them are of such great importance that every student of plants in cultivation should know something about them. There are hundreds of plants whose fibers might be used, but thirty or forty species at present supply the plant fibers of commerce. The most conspicuous are cotton and flax, the latter being used in the manufacture of linen. After these come the various hemps used for ropes, and the fibers used for matting. A brief account will be given of the origin and production of these most important fibers, and it will be easy to secure speci- mens of the " raw " fibers, showing how they appear when connected with their plants. 121. Cotton. — The cotton plant is said to be grown over a greater area, by a greater num- ber of people, and is useful for more purposes than any other fiber plant. Not only is its fiber exceedingly important, but its seeds yield important products, among which oil" is coming to be generally known. 411 FIG. 76. — Branch of cotton plant, showing foliage and flowers. — After W088IDLO. cotton-seed 412 ELEMENTARY STUDIES IN BOTANY Cotton is a member of the mallow family (Malvaceae), which is characterized chiefly by the fact that its numerous stamens grow together to form a tube that surrounds the pistil (Figs. 76 and 77). Associated with cotton in this family are such familiar plants as holly- hock, the mallows, abuti- lon, hibiscus, etc. The cotton genus (Gossypium) has numerous species, but only a few of them are cultivated for the fiber. The fiber occurs on the seeds in a fluffy, woolly mass (Fig. 78), and the seed- vessel is called the "boll" (really the fruit of the cotton plant). It is easy to obtain samples of these bolls, which burst open and allow the mass of fibers to emerge (Fig. 79). FIG. 77. — Section of a cotton flower, showing the large petals and ^the tube formed by the sta- mens. — After BAILLON. (l \ IVv M \vV& FIGS. 78 and 79. — Fiber of cotton : fig. 78, section of seed with fibers attached (after BAILLON) ; fig. 79, a cotton boll, burst and showing the mass of fibers (after BAILEY). The value of the fiber is due to the fact that it has a twist that makes it extremely well adapted for spinning. The various kinds of cotton differ in the quality and FIBER PLANTS 413 length of the fibers, the most highly prized being the Sea Island cotton, with its long and silky fibers. This cotton grows to the greatest perfection along the coast regions of South Carolina, Georgia, and Florida. There is also " up- land " cotton grown in the United States, whose fibers are shorter than those of the Sea Island cotton, but which can be cultivated over a much more extensive area than the finer cotton. In the market the various cottons are graded according to the length of the fibers. It is well known to every school boy and girl that a new epoch in the production of cotton was introduced by Whit- ney's invention of the cotton gin in 1793 ; and from that time the production of cotton in the United States has been an increasing industry in the southern states. In 1860 the United States furnished 79 per cent of the cotton used in Europe,, but during the Civil War it dropped to a little over 3 per cent; in 1900 it had risen again to 80 per cent. In 1911 the total cotton production of the United States was 14,775,000 bales, while the estimated production for 1912 was 13,000,000 bales. A standard bale weighs 500 pounds. It is interesting to compare the production of cotton in the various countries of the world, and also to compare its production in the various southern states. The total pro- duction of cotton in the world cannot be known, since a large amount is produced and used in countries where no records are kept. The following figures, therefore, deal only with those countries from which information can be obtained which is either exact or approximate. Taking only such countries into the count, the world's production of cotton in 1910 was about 20,000,000 bales. The comparison of cotton-producing countries in 1910 is as follows, the figures indicating the number of bales: United States 11,608,000, India 3,874,000, Egypt 1,570,000, China 1,200,000, Russia 688,000, Brazil 270,000, Mexico 200,000, Turkey 141,000, Persia 128,000, Peru 115,000. 414 ELEMENTARY STUDIES IN BOTANY In comparing the production of cotton by states, it is interesting to note the changes during ten years. In 1900 the record of the principal cotton-growing states, in the order of production, the numbers indicating bales of 500 pounds, was approximately as follows : Texas 2,610,000, Mississippi 1,240,000, Georgia 1,230,000, Alabama 1,000,000, South Carolina 840,000, Arkansas 705,000, Louisiana 700,000, North Carolina 440,000, Tennessee FIG. 80. — Map shaded to show the states of greatest cotton-production. 210,000, Indian Territory 145,000, Oklahoma 70,000, Florida 50,000; all other states nearly 30,000. In 1911, when the total production was approximately 15,000,000 bales, the seven principal states were as follows : Texas 4,200,000, Georgia 2,770,000, Alabama 1,700,000, South Carolina 1,650,000, Mississippi 1,200,000, North Carolina 1,100,000, Oklahoma 1,000,000, all other states about 1,400,000 (Fig. 80). 122. Flax. — There are numerous species of flax, but the common form in cultivation is a native of the Mediterranean FIBER PLANTS 415 region. It belongs to a small family (Linacese), which re- ceived its name from the' flax genus (Linum). The name of the common flax is Linum usitatissimum, which means " most useful flax." It is a low herb, with narrow leaves and handsome blue flowers (Fig. 81). It is cultivated for the fibers of its stem and also for its seeds. The fibers are long, fine, and very strong, so that it can be spun into very stout thread (linen thread) and woven into very durable cloth (linen) . This fiber is also used when especially strong twine or rope or sails are needed. Every one is familiar with the strong body of oil-cloth, which is woven of flax fiber. The seeds yield the well-known linseed oil, used for mixing paints and varnishes, and in various other ways. This very useful plant has been cultivated from the earliest times, but now its most extensive cultiva- tion in Europe is in Russia, Belgium, and Ireland. In the United States it has been cultivated for its seed ever since the first settlements, but lately it has attracted attention as a fiber plant, especially in Michigan, Wisconsin, Minnesota, North Dakota, and Washington. The world's production of flaxseed in 1898 was about 76,000,000 bushels, Europe producing 31,000,000 bushels, America 27,000,000 bushels, and India 18,000,000 bushels. In the same year the production of fiber was about 1,800,000 pounds, all of which is credited to Europe. About ten years later, in 1909, the world's production of flaxseed amounted to 101,000,000 bushels; and in 1912 the United States pro- duced about 28,000,000 bushels. FIG. 81. — A flax plant. 416 ELEMENTARY STUDIES IN BOTANY Russia leads all countries in the production of both seed and fiber, but the Belgian flax is the best, clue to the great care taken in its cultivation. . Flax demands greater labor than almost any crop, and its value for fiber is in proportion to the amount of intelligent care it receives. For fine fiber the seeds are sown thickly, so that the plants are crowded, and the young plants are pulled before the seeds are mature. For coarse fiber, the plants are given more room and pulled when the seeds are nearly mature. Usually the plants are pulled up by hand, roots and all, and the processes used for separating the fibers from the rest of the tissues need care and labor. Flax is said to exhaust the soil more than any other crop, so that much attention must be given to keep- ing the soil in proper condition. 123. Hemp. — Fibers from a great many plants are called hemp, but the common hemp, cultivated from the earliest times, belongs to the nettle family (Urticacea). Its name is Cannabis sativa, and it is a native of the warmer parts of Asia, but it has become naturalized in Europe and America. It is a rough herb, with palmately compound leaves (Fig. 82), and two kinds of flowers borne on different plants (dioecious). The staminate flowers are in open clusters, while the pistillate flowers are in compact clusters like a spike. The hemp plant has some strange associates in the nettle family. It is closely allied to hops, but in another FIG. 82. — A hemp plant. — After Internat. Encycl. FIBER PLANTS 417 section of the family are the elms, and in still another sec- tion are the figs, mulberries, and nettles. Hemp is cultivated for its fiber in all the countries of Europe, but its most extensive production is in central and southern Russia, which supplies the largest part of the world's hemp. In the United States it is cultivated to some extent, especially in Kentucky, Missouri, and Illinois ; but its production in this country has been greatly reduced by the introduction of Manila hemp. The fiber is used for coarser purposes than flax fiber, such as for ordinary ropes, for calking of vessels, etc. The seed is also produced in great abundance as " bird seed " for cage birds. The name " hemp " has been applied to the fibers of other plants which are used for the same purposes, the most con- spicuous of which are " bowstring hemp," " Manila hemp," " Sisal hemp," and " Sunn hemp." These will serve to illustrate the variety of plants whose fiber can be used in this way. Bowstring hemp received its name from its use in making bowstrings. The plant belongs to the lily family and is native in the tropical jungles of both eastern and western hemispheres. Manila hemp is from a species of banana growing in the Philippines, where it is extensively cultivated. It is a very strong fiber and has come to be used in the United States for binding twine and cordage. Sisal hemp is from an agave growing in Mexico, Yucatan, and the West Indies, and has been introduced into the Bahamas and Florida. It is second only to Manila hemp in strength. Sunn hemp is from a member of the legume family growing in India. It is not as strong a fiber as the other hemps mentioned above, but it makes fairly good ropes, canvas, etc. 418 ELEMENTARY STUDIES IN BOTANY 124. Suggestions for work. — Cotton " bolls " should be obtained, and the character of the fibers and their relation to the seeds examined. It should not be difficult, also, to obtain samples of various kinds of cotton fiber, " staples," as they are called. Flaxseed can be obtained in any drug store, and young flax plants can be grown and their fibrous character observed. Wild hemp may be growing in the neighborhood as a weed, and should be investigated. CHAPTER XII FORESTRY 125. Definition. — Forestry includes so many things that it is a difficult word to define. Primarily it means the care of forests, but it has often come to include also the care of individual trees. Both of these aspects will be considered here. A forest is often called " woods " in America, and the area covered varies from many miles in extent to the small " wood-lots " that remain in connection with many home- steads. The method of caring is the same whether a forest is large or small. The abuse of forests in this country is well known, but this is the common experience of new coun- tries. The time has now come when we have begun to realize the necessity of caring for our forests, and among the " conservation " movements, the conservation of forests holds a very important place. Forestry is an application of scientific knowledge, chiefly botanical, but including other sciences as well. Some indication of the many things a forester must consider will help to an understanding of his profession. Forestry includes not only such detailed care of forests as will be indicated later, but also the formation of forests where they do not exist, either because they have been re- moved (" deforestation ") or because they have never existed on account of unfavorable conditions. The forester must keep in mind always the purposes of a forest in relation to human welfare, which are principally (1) a source of timber and other products, and (2) to check floods that carry off soil. He must also know the best ways of using forests, 419 420 ELEMENTARY STUDIES IN BOTANY 4 and this includes " harvesting the crop/' putting it into the necessary forms, and disposing of the products. The general motive of forestry, which runs through all of its details, is to use the forest in -such a way that it may not only continue to be productive, but increasingly so. To insure this will require adequate protection of forest property, a more complete use of forest products, and harvesting with the future in mind. 126. Character of the forest. — An assemblage of trees is called a " stand," and stands may be pure or mixed. A pure stand is one in which all the trees, or nearly all, are of the same kind ; while a mixed stand is one in which there are various kinds of trees. There are three parts of a forest to consider in forestry : (1) the canopy, (2) the forest floor, and (3) the character of the tree trunks, which represent the mass of wood. The canopy is made up of the interlacing crowns of the trees, and it must be kept as uniform as possible. The value of the wood depends upon this, for a good canopy causes the lower branches to be shed while they are small, and as a result the trunk is clean and free from knots. In the formation of a forest, the forester sees to it that the canopy rises as the trees grow. In a pure forest a uniform canopy can be managed easily, but in a mixed forest the canopy is a more complex problem, for the different trees hold different relations to the light, some needing less light than others. In such a case the canopy is developed in stories in accordance with the light-needs of the different trees. The canopy serves several purposes in the economy of the forest. It manufactures the carbohydrate food for the trees ; it shades the forest floor and thus prevents the development of undergrowth, checks the drying out of the soil, and shields the soil from dashing rains ; it also enriches the soil with its leaf litter, making the forest soil the best of soils. FORESTRY 421 * The forest floor is not merely the surface of the soil, but also the whole soil region in which the trees are rooted. This is usually deep and rich, but, more than all, the humus gives it the physical properties of a sponge in receiving and retain- ing water. The character of the tree trunks is studied, not only to insure freedom from lower limbs by means of a suitable canopy, but also for the development of wood. Each tree has a period of development during which it adds annually to its wood mass enough to pay for the room and care it requires ; but eventually it reaches a stage when it is not mak- ing enough wood " to pay for its keep." The time to use a tree, therefore, is when it has reached its maximum wood- production and has not yet begun to decline. 127. Forests and floods. — Forests not only build up and enrich the soil, but they also fix the soil, a fact of great im- portance especially in a hilly country. The interlacing roots grasp the soil, so that roots and soil are knit together in a mass that resists erosion. It can be observed that hillsides from which the forest has been removed soon become gullied and stripped of soil. This protection against erosion serves not only for the soil in which the forest grows, but also for the soil of the fields at the lower levels. Forest soil holds water so persistently that heavy rains do not run off quickly and produce floods, as they do in bare regions. It is often remarked that streams that had a steady flow when a region was first settled have become alternately flooded and dry since the forests were removed. Therefore, the forest-covered soil not only prevents erosion of soil and flooded streams, but provides also a steady supply of water to the streams. 128. Formation of forests. — It would not be useful to give the details involved in the establishment of a forest where one does not exist, or in the making over of an in- ferior forest, but some idea of the things involved will add 28 422 ELEMENTARY STUDIES IN BOTANY to one's information as to the work of a forester. Sometimes the soil must be reclaimed by draining it if swampy, and by putting it into better physical condition if necessary. Great judgment must be used in the selection of trees for a given region, and in the decision whether it is better to establish .a pure or a mixed forest. The seed used must be tested thoroughly for quality, and the care of seedlings is full of details. In general, the germination of seeds and the care of seedlings are best provided for in reliable nurseries. In making over a forest of inferior quality, the problem is to give seedlings a chance to grow and to replace the old and inferior trees by young and vigorous ones. Of course each forest has its own problems, but enough has been stated to indicate how a uniform stand may be secured in making or reclaiming a forest. 129. Care of forests. — The care of a forest means keep- ing it in good condition. " Cleaning " a forest means the removal of useless trees, useless because they are dead or injured or old or unpromising, and the removal of other plants and of brush that interfere with the proper condition of the forest floor. " Thinning " a forest means the removal of certain trees to prevent the trees from interfering with one another. This interference is mostly a question of an over-crowded canopy, for the crowns must expand freely and interlace, but must not interfere with one another's development. Sometimes pruning is helpful, but this is not practicable in a large forest as a general performance. The advantage of forest growth in the production of wood as contrasted with isolated trees should be understood. A tree " in the open " is often thought of as the best developed tree, which may be true so far as its general appearance is concerned ; it satisfies best our idea of how a tree should look. But if a tree is expected to produce wood of good quality, it must be associated with other trees so that a good canopy is developed. A tree in the open produces FORESTRY 423 more wood, but it is poorer in quality because the lower limbs are allowed to develop and the wood is full of knots. 130. Protection of forests. — The protection of forests is one of the most difficult problems of forestry, for it involves the passing of laws and their enforcement, and the hearty cooperation of communities. This is especially true of pro- tection against fire, which is the greatest enemy of the American forest, and is mostly the result of ignorance, care- lessness, or indifference. The fierce fires in the white pine regions of Michigan, Wisconsin, and Minnesota have become familiar, and sometimes they involve extensive destruction not only of valuable trees, but also of human lives. In the great Minnesota fire of 1904 it is reported that 600 lives were lost. An investigation of the causes of these recurring forest fires has shown that sparks from passing locomotives are the chief cause. It is evident that this cause of fires can be controlled if public sentiment becomes strong enough. Another prolific cause of fires comes from the carelessness of campers and hunters, a cause that is troublesome to check. Farmers often " clear the land " by fire, and carelessness or lack of judgment may result in permitting the fire to extend into the adjacent forest. The effect of a fire differs in its destructiveness. It may involve only the canopy ; it may run over the surface of the soil ; or it may be fierce enough to burn the humus of the soil. In any case, the forest is crippled, and in the last case not only are the trees destroyed, but the soil is no longer fit for forest growth. The danger of hard freezing is also to be considered, for it may kill the buds, crack the stems, and upheave the young plants. Frost cracks in lumber show that damage from this cause is often serious. The trees cannot be pro- tected from such a danger completely, but a dense canopy reduces it, and a thick litter of decaying leaves (humus) on the forest floor is still further protection. Damage is also done by violent winds, hail storms, sleet, and snow, but 424 ELEMENTARY STUDIES IN BOTANY these are the accidents of nature that involve only a repair of the damage. There are many insects which are very destructive to trees because they bore into «the wood or eat the leaves. The gipsy moth has become famous for its leaf -destroying powers. The best protection against insects is to encourage their enemies. A forest full of birds, toads, snakes, etc., is well- protected against destructive insects. The need for such protection justifies the exclusion of hunters from forests under cultivation, especially the men who shoot at everything. The problem of grazing animals in a forest is a mixed one. These animals are usually sheep, and up to a certain num- ber they may not be injurious, and may even be helpful, but in large numbers they are injurious, being not only grazing but also browsing animals. The danger to forests from plant diseases will be con- sidered in the next chapter, which deals with plant diseases in general. 131. Forest products. — It is a surprise to many to dis- cover the number of uses to which forest trees are put. Most people probably think of forests only as a source of lumber, so far as their commercial use is concerned. It is true that lumber is the conspicuous product, arid it is known that this lumber is put to endless uses. For this purpose, trees are grouped as " soft woods " (pine, spruce, hemlock, cedar, etc.), belonging to the conifer group (called " ever- greens " by many), and " hard woods " (oak, walnut, hickory, cherry, locust, tulip-tree, ash, maple, elm, cottonwood, etc.). The lumber industry in soft woods may be used as an illus- tration. The most prized soft wood is the white pine, and the important white pine states are Michigan, Wisconsin, and Minnesota. This valuable tree has been harvested so recklessly that it has now approached dangerously near the point of extinction as a commercial source of lumber. The lumber camps, logging operations, and the floating out of FORESTRY 425 the lumber are important features of these states, and have developed a type of life and a race of hardy men (chiefly French Canadians) who have appeared in many stories. In the south the yellow pine is the great soft wood. As it grows in an open, level forest, the logging operations differ from those of white pine, and are by no means so picturesque. The logs are simply hauled to the railway or mill, and the work is done chiefly by negroes. The third great region for soft wood lumber is in the northwest, in the Douglas spruce and redwood forests of the Pacific slope, where the immense size of the trees and the roughness of the ground have neces- sitated special methods and machinery entirely unknown in other regions. The use of wood pulp in the manufacture of paper is a tremendous industry. The most commonly used wood is spruce, and the process consists in grinding the wood (from which bark and knots are removed) into pulp and pressing it into paper. This pressed pulp, aside from paper manu- facture, is used in the manufacture of a great variety of articles, as buckets, doors, and even wheels. In the manu- facture of paper it is estimated that one ton of paper pulp is produced by one and a half cords of wood. The amount of this paper used by newspapers is enormous. It has been estimated that one large newspaper uses in one year all the spruce grown on 16,000 acres of land, as spruce naturally grows. If this amount be multiplied so as to include all the newspapers, it is evident that the supply of spruce will fail. Of course other woods can be used for the same purpose, Carolina poplar making very good paper pulp. The pines are used as the source of resin and turpentine, which occur in " crude resin " in the resin ducts of the wood. The largest supply of this product comes from the pine forests of the south, but in collecting it the trees are so handled that they are destroyed. In France the product is obtained without destroying the trees, and unless some such method 426 ELEMENTARY STUDIES IN BOTANY is introduced in the southern pineries, the resin industry is doomed to destruction. The bark of certain trees is also used as a source of tannic acid for tanning leather. In Europe, oaks are extensively propagated for this purpose, but in the United States hem- lock bark is used. With our usual recklessness the trees are practically destroyed in securing the bark, so that now a large amount of our tannin comes from South American woods. The destructive distillation of woods yields a remarkable variety of products that need not be enumerated, chief among which are wood alcohol and tar (from the distillation of pine). In every case, after the desired product has been driven off by distillation, charcoal is left. Any consideration of the products of trees must include maple sugar and syrup. This is said to be the only forest industry that has been developed on a scientific basis. It is an American industry, and when it is known that over 50,000,000 pounds of sugar and 3,000,000 gallons of syrup are produced each year, it can be appreciated that the indus- try is a large one. Vermont is the leading state in maple sugar production, producing 15,000,000 pounds of sugar and 100,000 gallons of syrup in a year. In this connection mention may be made of the common sources of commercial sugar. Sugar-cane (a grass) has been used longest as a source of sugar, and in this country the industry has been most developed in Louisiana. The manufacture of sugar from beets is a much newer industry, and has developed on a large scale in the United States. In the production of sugar from sugar-cane, India leads the other countries, followed by Cuba, Java, and the United States. The world's production of sugar from cane in 1903 is estimated to have been about 4,000,000 tons ; and of sugar from beets about 5,800,000 tons, 5,600,000 tons of which was produced in Europe. In 1911 the production of sugar from FORESTRY 427 cane had reached 7,600,000 tons, and from beets 8,400,000 tons. Another use of forest products has yet to be developed in the United States. In Europe every twig is used ; that isr the forest refuse, which we destroy as " brush," is all utilized. To use this material seems to the American a waste of time, involving an amount of labor that is not paid for by the result; but since many uses for forest refuse have been developed in European countries, there is no reason why some of them may not be introduced here. 132. Forest reservations. — The great importance of exercising some control over forests has led the national government to adopt a system of forest reservations, which are under its care. To a certain extent, states have done the same thing, but it will be impossible to include them in this brief statement. It is not the purpose of the govern- ment to withdraw such forests from use, but rather to super- vise their use so that they may continue to be productive. Furthermore, some forests are reserved by the government not so much for the sake of a continuous timber supply, as to protect certain regions from floods and soil destruction. Naturally such forests are found on the important water- sheds of our drainage systems. These reservations are so fluctuating in extent, depending upon the attitude of the president towards forest reservation, that it is impossible to give their exact extent as a general statement. Some conception of the forest areas involved, however, and their distribution may be obtained from the following statement of the reservations in 1901, the begin- ning of such reservations being in 1891. The statement, therefore, covers the period of the first ten years of forest reservation. During that period nearly 50,000,000 acres of forest land were reserved, distributed among 13 states. The list of states, the number of reservations, and the approximate number of acres involved are as follows, in 428 ELEMENTARY STUDIES IN BOTANY the order of total size of area in each state : California, nine reservations, 8,750,000 acres ; ' Washington, three reserva- tions, 7,000,000 acres ; Arizona, four reservations, 5,000,000 acres ; Oregon, three reservations, 4,750,000 acres ; Montana, three reservations, 4,500,000 acres ; Idaho and Montana, one reservation in common, 4,000,000 acres ; Wyoming, four reservations, 3,250,000 acres ; Colorado, five reservations, 3,000,000 acres; New Mexico, two reservations, 2,750,000 acres ; South Dakota and Wyoming, Black Hills reserva- tion, 1,200,000 acres; Utah, three reservations, 1,000,000 acres ; Idaho and Washington, one reservation in common, 650,000 acres ; Alaska, one reservation, 400,000 acres ; Oklahoma, one reservation, 60,000 acres. This list includes 41 reservations set apart as forests ; but since 1901 the amount of reservation has been very much increased, the total area in 1912 approximating 190,000,000 acres. An illustration of the increase can be obtained from Alaska, whose area of reservation increased from 400,000 acres in 1901 to 27,000,000 acres in 1912. 133. Street trees. — Even though the reader of this book may not have access to a forest, where forest conditions can be observed, he can at least observe trees growing in yards or along streets. In fact, the study of trees, even in cities, is not only possible, but interesting and profitable. There is nothing more neglected than street trees, and it will be helpful if school pupils are taught to know something about their care. The streets fitted for tree-planting usually provide a planting strip between the sidewalk and the curb ; and in a very wide street a parking strip in the middle is often seen. Much street planting has been done independently by the owners of different lots, so that the trees are of various kinds and the result is a ragged appearance. If possible, a reason- able uniformity in the kind of tree used improves the ap- pearance of a street very much. Not only should the trees be of the same kind, but their spacing should be uniform, FORESTRY 429 and this differs for different trees. The spacing should be a little greater than the natural spread of a tree ; for example, the following spacings are recommended : white elm, 50 feet ; maples, 40-45 feet (dependent on the kind) ; linden, 40 feet ; Carolina poplar, 30 feet. The selection of trees is important, and the judgment of different people will vary. The primary choice is between a fast-growing tree and a slow-growing tree. The former brings results quicker, which mean beauty and shade, but it is usually a short-lived and brittle tree. The latter de- velops beauty and shade very slowly, but it is usually long- lived and tougher. It would seem wise to select for city streets the slow-growing and long-lived trees, the most popu- lar of which is the white or American elm. The rapid-grow- ing trees, which impatient people select, are usually Carolina poplar, willow, box elder, or silver maple. 134. Planting street trees. — The space for soil prepara- tion is very restricted, so that instead of breaking up the soil in the usual way for a crop, large holes are dug and filled with proper soil, which in this case means a pulverized soil thoroughly mixed with fine manure. Great care must be taken to see that there is proper drainage, and often a tile drain has to be laid. The young trees are usually obtained from a nursery, and before they are " set," they are pruned, so that the stem system may balance better the more or less injured root system. In case the root system is com- plete, no trimming is necessary, but it would be a rare amount of care that could transplant a young tree without injuring the roots more or less. In the bottom of the hole a bed of fine soil is placed, the tree is settled in place care- fully and watered, and the hole filled up. Of course trees must be transplanted while they are dormant, and this means either spring-planting or fall-planting, the former being the better. Sometimes very large trees are trans- planted, but the larger the tree, the greater the danger. 430 ELEMENTARY STUDIES IN BOTANY 135. Care of street trees. — In observing most street trees, one might infer that after the trees are planted they need no attention. While they need little attention after they are full grown, the young and growing trees cannot be neglected. Perhaps the greatest cause of failure in the growing of street trees is the poor physical condition of the soil, a thing which the reader of this book might infer. The soil, therefore, must be kept in good physical condition around the young trees, and since the feeding ground of street trees is much restricted, certain fertilizers are a great help. It is evident that the cultivation of the soil beneath the tree helps the movement of air through the soil and helps the soil retain moisture. If there is sod around a tree, it should be broken up every few years. Of course street trees must be pruned, and pruning is done while the tree is dormant. In connection with pruning, the large wounds (over two inches in diameter) must be cared for, or they will permit the entrance of destructive fungi. They are dressed with something that excludes fungi, as thick paint or coal tar. When a wound is very large (over six inches in diameter), it is usually covered after treatment with a zinc plate, a process called " tinning." Wounds less than two inches in diameter usually heal up before the fungi effect an entrance. 136. Injuries to city trees. — There are many sources of injury to city trees, due chiefly to city conditions. Smoke poured out abundantly from smoke stacks, and gas from leaking pipes escaping into the soil about the roots, are common causes of dead and dying trees seen along streets. Electric linemen are often reckless in chopping out branches to clear the way for wires. Trees are also often seen to be used for anchoring guy ropes. Regrading streets often de- stroys trees ruthlessly and needlessly. Ignorant pruning probably destroys more trees than any other danger, not only because the pruning is wrong, but also because the FORESTRY 431 wounds are not cared for. The old days of using trees for hitching posts and subjecting them to wounding by horse bites have nearly passed. Of course storms are to be reckoned with, and a sheeting of ice breaks many twigs and even large limbs. The best protection against damage from such storms is to select for street trees those that are not brittle. The Carolina poplar, willow, and silver maple are notably brittle, and after a storm the ground beneath them is strewn with a litter of branches. 137. Suggestions for work. — If a forest is available, it should be visited by all means. The trees should be named, the crown examined, the uniformity or irregularity of growth noted, and judgment passed as to the condition of the forest and its needs. Special pains should be taken to learn to recognize all the common street and yard trees in the vicinity, both in their winter condition (from their habit and bark) and foliage condition. Street trees should be examined to discover their condition and the care they are receiving ; if any work is being done with them, it should be watched. If trees are sickly looking, the cause should be inquired into. This kind of interest in street trees will stimulate the community to a more intelligent care of them. CHAPTER XIII PLANT DISEASES 138. Definition. — In the cultivation of plants there must be some knowledge of the diseases to which they are subject. Sometimes whole crops are destroyed by some disease, or at least much reduced in quantity and quality. The great losses from this cause have led the national and state gov- ernments to provide for the study of plant diseases in the hope of preventing them. Very much has been accom- plished, but very much more remains to be done. A multi- tude of facts in reference to diseases and treatments have been accumulated, but these cannot be detailed here. Only the general facts in reference to plant diseases and the general principles of treatment can be indicated ; for special details the student must consult the larger works in which the known facts are assembled. It is difficult to define exactly what is meant by a plant " disease." In a large sense it is anything that interferes with the normal activities of a plant, so that it is not " doing well." It is evident that this would include a great variety of causes, such as soil conditions, climatic conditions, me- chanical injuries, attacks of animals (especially insects), and attacks of parasitic fungi ; in fact, anj^thing that affects unfavorably the vigor of a plant. It is clear that we can include no such indefinite range of causes, and must restrict ourselves to the diseases induced by parasitic fungi, for these are the most common and most studied of the diseases. The distinction between a disease and its cause must be kept clear. A parasite (like wheat rust, for example) is a cause, but the disease is the condition of the attacked plant 432 PLANT DISEASES 433 (host) brought about by the presence of the parasite, a con- dition which is more or less unfavorable to the work of the plant. This means that while we investigate the parasite to discover its habits, the patient that has the disease is the host plant. The study of plant diseases, therefore, so far as plant parasites are concerned, is the study of the effect of the parasite on the host plant. The practical application of our knowledge of parasites and diseases has not resulted so much in curing diseases as in preventing them, which means preventing the attack of parasites. This involves enough knowledge of the parasite to know the form in which it makes its attack, as well as the part attacked and the time of attack. 139. The groups of parasites. — Almost all of the groups of fungi contain parasites that are dangerous to cultivated plants. These parasites are more or less selective, that is, they do not all attack all plants indiscriminately. Each parasite is more or less restricted to certain hosts, and often to a single host. This explains why one kind of plant is subject to a certain disease (" susceptible "), and another is not (" immune "). The groups of parasites are very numerous, and it would be impossible for an elementary student to learn to recog- nize them ; but this is not important for our purpose. All that is necessary in this first contact is to learn to recognize certain " symptoms " of disease which attacked plants show. Any symptom suggests troubles which may be brought about by a great variety of parasites, and it is not always necessary to distinguish the -parasite exactly before using the appropriate preventive measures. 140. The groups of diseases. — All plant diseases can be referred to three groups, which differ as to the relation of parasite and host. In one group, the parasite kills living cells, and its de- structiveness depends upon the number and kind of cells 434 ELEMENTARY STUDIES IN BOTANY killed. A plant attacked by such a parasite may live along in a more or less enfeebled way, or it may be destroyed completely. In a second group, the parasite does not kill living cells, but lives in association with them, feeding upon their prod- FIG. 83. — A spot disease of apple leaf. — After SORAUER. ucts. Often as a result of the presence of such a parasite, the living cells are " stimulated " into doing unusual things, such as the development of " galls " or other unusual growths. Such growths are symptoms of the presence of such a para- site. This peaceful living together is usually brought to an end when the parasite begins to form spores. PLANT DISEASES 435 In a third group the parasites neither destroy living cells nor live peaceably with them, but invade the water-conduct- ing vessels (woody fibres) and live in the sap. This inter- feres with the movement of water, and if the parasites develop so as to block the vessels, the water supply is cut off and the plant wilts. These " wilt diseases " are very common and destructive, especially in the case of seedlings. Fiu. 84. — A spot disease of maple leaf. — After SORAUER. 141. Diseases of the first group. — In this group of dis- eases the parasite kills living cells. No list of these diseases can be given, but a few representative cases will illustrate them. Pear blight. — This is one of the common diseases, not only of pear trees, but of apple trees and other fruit trees. It is sometimes called " fire blight " or " twig blight," and these names suggest the appearance of trees with this dis- ease. The flowers and branch tips begin to wilt and finally blacken, and this may extend to every branch tip, until the 436 ELEMENTARY STUDIES IN BOTANY tree appears as though its branches had been badly scorched with fire. This disease is caused by certain bacteria that spread through the living cells' and destroy them. It is always necessary to determine how a parasite effects an entrance in a plant, for this suggests the method of preven- tion. The entrance of a parasite is spoken of as an " infec- FIG. 85. — A spot disease of currant leaf. — After HALL. tion," and in the case of pear blight, it is found that the infection is brought about by insects (especially bees) visit- ing the flowers. This infection spreads to other flowers and through them into the young twigs. Just how the insects get the bacteria is a detail that is not needed for practical purposes. Spot diseases. — It is very common to see leaves spotted, PLANT DISEASES 437 the spots indicating that they have been attacked by some fungus (Figs. 83-87). Among the parasites that produce spotted leaves are the " mildews." One kind of mildew is called the " downy mildew" because it appears on the sur- face (usually leaf) of the host plant as small downy patches. FIG. 86. — A spot disease of strawberry leaves. — After MASSEE. These patches are numerous minute branches bearing spores, that have arisen from the parasite deep within the host, where it is destroying living cells. Before the downy patches appear, the presence of such a parasite in a leaf is shown by the dying and dead spots. This attack on leaves reduces their ability to manufacture food, and it may be so general an attack that the leaves are destroyed entirely. Such 29 438 ELEMENTARY STUDIES IN BOTANY attacks are common on many vegetables, as radishes, tur- nips, cucumbers, onions, lettuce, etc., but the most con- spicuous case is that of the grape (Fig. 88). These mildews represent one of the most destruc- tive of the "dis- of the eases grape-vine, the FIG. 87. — A spot disease of beet leaf. — After HALSTED. most susceptible grape being the wine grape ( Vitis vinifera) of Eu- rope and Cali- fornia. In the account of the grape (p. 396) it was stated that the wine grape could not be grown in our eastern states on account of this disease. It can be grown in Eu- rope and Califor- nia because for some reason the destructive mil- dew is absent or is harmless. Infection in this case is by spores that fall upon young leaves, and the suggested pre- vention is to destroy the spores in some way before they can effect an entrance. PLANT DISEASES 439 Another kind of mildew (" powdery mildew ") attacks the young grapes, producing corky spots that destroy the value FIG. 88. — Grape leaf, showing patches of downy mildew. of the fruit. This spotting of the fruit does not destroy the plant, for it is only a skin disease, but it destroys the value of the plant for our use. 440 ELEMENTARY STUDIES IN BOTANY Potato disease. — This is a notable and dangerous disease. Famines in Ireland have been brought about by its ravages, because in destroying the potato crop there were no other crops to replace it as a food supply. The spores of the parasite enter the young leaves and they begin to spot (Fig. 89), and fi- nally the parasite invades all the leaves and the young stem, and the plant dies. The disease is so very epidemic that if it enters ^v-.-£,- ••-*>* a potato field, it ^fH Ifc B f^ life. sweeps through it H W* w^ great rapid- ^^^SBB mr ' ity. If the attack is early in the sea- fj^i5^ son, the formation % of tubers may be ^j| . stopped; if it is later, the tubers may have begun to develop, and in this case the tubers also are in- vaded. Tubers in this condition are said to have the " potato rot" (Fig. 90), but the rotting is not caused by the destructive parasite ; it is merely the natural rotting of a plant structure that has been killed. This is one of the hardest diseases to prevent, for since potatoes are propa- gated by tubers, the danger of infected tubers is very great. FIG. 89. — Potato disease on the leaves. — After JONES. PLANT DISEASES 441 Stone fruit diseases. — The common disease of stone fruits is the " brown rot," and probably its destructiveness is noticed more in the case of peaches than in any other one of the stone fruits (plum and cherry), many of the " failures " of the peach crop being due to it. Along with the peach FIG. 90. — Potato disease ("potato rot ") in tubers. — After DUGQAK. are associated its near relatives, the apricot and the nec- tarine. In this case the fruit is infected directly by the spores of the parasite, and it seems to be most susceptible from the time it is half grown until it ripens. The first symptom of the attack is a small, brown, decayed spot which increases in size until the whole fruit is infected. Often the 442 ELEMENTARY STUDIES IN BOTANY fruit is completely dried out, and such " mummies/' as they are called, may be seen hanging on the trees. It should be realized that these mummies are exceedingly dangerous, for they are the chief source of infection the next year. Often infections are so late that the disease is not detected until after the fruit is picked and shipped, in which case a lot of slightly specked fruits when shipped may arrive as mum- mies or nearly so. Cankers. — These are diseases that arise in connection with open wounds, and are con- spicuous in trees (Fig. 91). Some knowledge of cankers is of great practical importance in the handling of forests and orchards. As they are wound diseases, it is evident how the parasite enters, and the wounds are formed in nature by storms, and in cultivation by trimming and bruising. If the wound is small, it may heal naturally ; but if it is large, it may remain as an open wound, exposed to continuous infection. Bitter rot. — This is a very destructive disease of apples and other fruits, and is known wherever -apples are culti- vated. It is recognized by the characteristic spot it forms on apples. It is at first small, increases rapidly in size, turns FIG. 91. — Canker on apple tree. — After SORAUER. PLANT DISEASES 443 brown, and becomes sunken through rotting of the tissue (Fig. 92) . These spots may be recognized from other kinds of spots by their sunken appearance, their bitter taste, and their ringed border. This disease was observed for many years before the method of infection was discovered. Now it is known that the parasite is a wound parasite that develops cankers on the twigs (Fig. 93). Abundant spores are formed in these cankers and are washed down by rains on the fruit FIG. 92. — Bitter rot of apple. — After CLINTON. below. It had long been noticed that a sudden attack of bitter rot was brought about by a few rainy days. 142. Diseases of the second group. — In this group of diseases the parasite does not kill living cells, but lives on their products and often induces them to develop unusual structures. Rust. — This is a very conspicuous disease of cereals, in which the parasite and host live peaceably together for a time, but in which there is usually no abnormal growth. The " disease," therefore, consists in the gradual weakening of the living cells by the drain upon their food supplies, until finally they can work no more and are destroyed by 444 ' ELEMENTARY STUDIES IN BOTANY the parasite. It is easy to discover this trouble, for the rusty patches of spores become abundant on the leaves and stem of the host plant, but the cure seems hopeless, and preven- tion is uncertain as yet. Crown gall. — This is a very common bacterial disease of trees and shrubs, and among cultivated plants it is note- worthy in the various fruit trees and street trees. As the name implies, the symptom of the disease is the develop- ment of a gall-like growth (tumor) on the " crown " of the FIG. 93. — Canker of bitter rot on apple twigs. — After BURRILL. plant, which means the base of the stem where it joins the root (Fig. 94). During the autumn and winter the gall disintegrates and leaves an open wound. At the margin of an old gall, new galls arise, and so the wounds are en- larged from year to year. A most interesting fact has been discovered in connection with these galls, and that is that they give rise to a disease- carrying tissue (" infecting strands ") that penetrates to other regions of the plant and gives rise to new galls. This makes it impossible to remove the trouble by surgery, for while galls may be removed and the wounds healed, the " infecting strands " are spreading the trouble into other regions. The whole trouble begins by some wounding or PLANT DISEASES 445 bruising of the crown that permits the gall-forming bacteria to enter. Peach leaf curl. — It is a frequent trouble in peach orchards that the leaves become curled up and twisted into various shapes, the surface looking wrinkled and blistered. This interferes with the work of the leaves so much that there may be an extensive failure of the crop. This curling and twisting is due to the fact that the presence of the parasite causes the leaf cells to grow very un- evenly. Black knot. — This is an exceedingly common disease, and among cultivated plants it is most commonly seen on plum (Fig. 95, a) and cherry trees, but it is common also on shrubs, as currants (Fig. 95, 6) and gooseberries. It appears as small hard knots or " warts " that break through the bark and finally become dark brown or black. The knot is made up of a mixed mass of cells devel- oped by the host plant because of the presence of the fun- gus, and interlaced in the tissues of the knot is the thready body of the parasite. The twigs of the plant may not be killed, but when they are girdled by knots they are destroyed. 143. Diseases of the third group. — In this group of dis- eases the parasite invades the water-conducting vessels and FIG. 94. — Crown gall on daisy. — After ERWIN SMITH. 446 ELEMENTARY STUDIES IN BOTANY lives in the sap, cutting off the water supply and causing the host plant to wilt and die. Since the first symptom of the presence of these parasites is the wilting of the host, these diseases are known in general as " wilts." There are a great many kinds of wilt-producing fungi, but their relation to the host and their effect upon it are the same. A few illustrations will be given. Cabbage wilt. — In this disease, the water-conducting vessels are invaded by bacteria that enter through the " water pores " of the leaves, which are minute openings along the edges of the leaves that are connected with the system of water-conducting vessels. They are in fact the open terminals of this system. The disease is often called the " black rot of cabbage " (Fig. 96), but the rotting is not due to the wilt-producing bacteria, but to the decay of the leaves or of the whole head which they have been the means of killing. Cucurbit wilt. — This is often a very destructive disease among In this case there is no natural opening for the entrance of wilt-producing bacteria, as in cabbage, but the infection is through wounds produced by the bites of insects. From the point of entrance the in- fection extends through the vessel system. If the infection is at the tip of a branch, the wilting is gradual ; if it is in the main stem, the wilting is rapid. Fusarium wilts. — Bacteria are not the only fungi that FIG. 95. — Black knot: a, on plum b, on currant. — After MASSEE. melons and cucumbers. PLANT DISEASES 447 produce wilt diseases. Among the other wilt-producing forms are the Fusariums. Under this head come three dis- eases of great importance in the south, namely the wilts of cotton, cowpea, and watermelon. The Fusarium is a soil fungus, so that the infection is probably what is called a " soil-infection," the most difficult kind to guard against. FIG. 96. — Black rot of cabbage: c, healthy plant; s, diseased plant. —After HARDING. It means that the soil of a field becomes infected, and that continued planting on that area simply increases the in- fected area every year. Another notable Fusarium wilt is the flax wilt, which is the great enemy to the raising of flax. Fusarium-infected soils are often spoken of as " sick soils," as " cotton sick," " flax sick," etc. Mushroom wilts. — These are our most important tree diseases, and since they are wood-destroying diseases, they are of great importance to the forester. The invading 448 ELEMENTARY STUDIES IN BOTANY fungus is a mushroom (Fig. 97), which enters the tree by its spores lodging in wounds, or penetrates directly into the tree by way of the soil. In either event, the wood- vessels are in- vaded, and the destruction of wood is due to the action of sub- stances formed by the fungus. In this way the various "rots" of trees are brought about. 144. Control of diseases. — All of the study of plant diseases has for its purpose the control of dis- eases. It is evi- dent that this is a vast and com- plicated subject. A great many " treatments " are suggested that are not based in knowledge; they may do good, or they may be useless. Naturally, people use any treatment that may do good, rather than no treatment at all. But as the knowledge of plant diseases increases, treatments are FIG. 97. — Tree fungus on aspen. — After VON SCHRENK and SPAULDING. PLANT DISEASES 449 becoming more and more intelligent and effective. There are a few general principles that lie at the basis of any intel- ligent and effective treatment, and these principles should be known to all who cultivate plants. 145. Infection. — No intelligent control of disease is pos- sible without exact knowledge of the sources of infection. A good illustration of the truth of this statement may be obtained from the case of peach curl. For a long time it was supposed that the infection came from a parasite that lived year after year in the peach tree, and therefore that no control was possible. But when it was found that the infection came from spores that lodged on the buds, thus getting a chance at very young leaves, the control became obvious and easy. It is well to recall the various sources of infection known, and to remember that they are not yet known in the case of most diseases. There are soil infections, the parasites living from season to season in the soil ; spore infections, in which spores are carried by the wind, by insects, by rain- drops, by seeds, etc. ; wound infections ; and infections by parasites that live from season to season in the host. There are also parasites on the surfaces of host plants, and para- sites within the tissues of host plants; the former can be treated easily, and the latter not. 146. Fungicides. — A fungicide is a substance that kills fungi. It is applied usually either as a powder or as a liquid, and it is obvious that its application depends upon whether the fungus can be reached. The obvious conditions for application are when the parasite is a superficial one, or when its spores are lodged somewhere on the surface of the plant. Such applications are clearly not appropriate in the case of soil infections, or in the case of parasites living per- manently within the tissues of the host. It should be remem- bered, also, that some fungicides injure some plants, so that their use upon them, no matter what may be the position of the parasite, is impossible. 450 ELEMENTARY STUDIES IN BOTANY The list of fungicides is a long one, and would not be appropriate here. Their names and their composition can be obtained easily if needed. The most famous and the most generally useful is called " Bordeaux mixture," which was discovered in connection with the ravaging of European vineyards by mildew. It is a mixture of copper sulphate and lime. When it is discovered that a fungicide is appropriate, the next thing is to know when to apply it. This can be made plain by a few illustrations. The grape mildew infects the grape-vine by means of its spores falling upon young leaves. Accordingly, the young leaves are sprayed with the fungi- cide, and this treatment has proved to be completely effective in controlling the disease. The case of potato disease (" potato rot ") is somewhat different. Here also the disease is spread by wind-blown spores, which infect young leaves. Therefore, early spray- ing of potato plants with Bordeaux mixture checks the spread of the disease. But the more serious trouble comes from the infected tubers which pass the disease on from generation to generation. The fungicide treatment in this case, therefore, does not eliminate the disease, but simply checks its spread. In the brown rot of stone fruits, the infecting spores are lodged on the bark and leaf buds. It follows that these spores should be destroyed by the application of a fungicide in late winter or early spring. In brown rot, in addition to spores lodged on bark and leaf buds, there is danger of infec- tion from mummied fruits hanging on the twigs or fallen on the ground, and it is evident that all such fruits should be destroyed. Of course the powdery mildews, such as attack grapes and induce a skin disease of the fruit, are easily reached and killed by a fungicide while the fruit is young. These illustrations will serve to indicate what is meant PLANT DISEASES 451 by the statement that fungicides are appropriate only for certain parasites ; that in each case there is a most effective time for their application ; and that in some cases they are only of supplementary use, not reaching all the sources of infection. 147. Surgery. — This means the removal of infection and guarding against further infection. Perhaps no treatment of plants is done more thoughtlessly and needlessly than surgery. Before any such operation, one must be sure of three things : (1) whether the infection exists in the part proposed to be removed; (2) if so, whether it will do any good to remove it ; (3) and if so, whether it can be removed. A few illustrations will make this plain. In the case of pear blight, the flowers are infected by in- sects that obtain the bacteria from certain affected branches in which they have passed the winter. It happens that these branches show their character, for they are " blighted. " It is obvious that such branches must be pruned out before the opening of the flowers. Crown gall was once thought to be a case for surgery, but now it is shown that the removal of a gall (tumor) is in- effective because there are infecting strands (p. 444) which cannot be removed. This illustrates a case in which the infected area is known, but it cannot be removed. The only surgery useful in crown gall is to destroy all affected nursery stock. One of the most common applications of surgery is in connection with the treatment of wounds on trees, to prevent cankers and invasions of the water-conducting vessels. A race of " tree surgeons " has been developed, some of whom are reliable, and others are ignorant of their business. The general method is to clean out the wound so that a fresh surface is exposed for healing, and then to cover it so as to prevent the entrance of wound-infecting fungi. 148. Soil infection. — When soil infection is involved in 452 ELEMENTARY STUDIES IN BOTANY any disease, it is peculiarly hard to control. Once the use of soil fungicides was recommended, but since we have learned something about the soil, this has been shown to be a very dangerous proceeding. The soil is swarming with bacteria and other fungi, many of which are extremely im- portant, and fungicides cannot pick out one organism for destruction and leave the others alive. Such a treatment is much like annihilating the population of a city to get at one criminal. There is no evidence, as yet, that any so- called soil fungicide does any good. If fungicides are not available for soil infections, such as occur in numerous wilt diseases, what can be done? In the case of garden crops, as cabbage, infected plants can be re- moved or destroyed, but in the case of field crops this is impracticable. The only known method of controlling soil infection is to stop planting the susceptible crop on the infected area, and to plant some other crop. This rotation generally eliminates the infection or weakens it. 149. Uninfected stock. — In all cases of infection by parasites living from one season to the next in a plant, the only safe thing to do is to see to it that seeds or tubers or cuttings used in propagation are obtained from absolutely uninfected stock. This has been tried with the potato dis- ease and found to be most effective. 150. Resistant races. — The breeding of races of plants resistant (" immune ") to the different diseases is the final resort in the matter of control. When nothing else avails, the cultivation of immune races must be resorted to. Prob- ably this will be the final remedy for all our plant diseases, but those that can be controlled can afford to wait. For this reason, the work on resistant races as yet has had to do chiefly with diseases that arise from soil infections. The following illustrations indicate that some progress has been made. In the case of the potato disease it was shown how a PLANT DISEASES 453 fungicide, like Bordeaux mixture, can be used on very young plants to reduce the spread of infection during a growing season ; but the more serious trouble is in the soil, from infected tubers. It was in connection with this im- portant disease that the first attempts were made to develop resistant races, and many have been obtained. The trouble has been that resistant races do not continue to be resistant, and in a few seasons they are no more resistant than other races. Also, the resistant races have not proved to be re- sistant in all localities. In the case of the Fusarium wilts, as of cotton, the cultiva- tion of resistant races began seven or eight years ago, and in four or five years success was attained. Several resistant races of cotton, and also of cowpea, were secured. As in the case of resistant races of potato, however, the resistant races of cotton have not always retained this character in all localities. The discovery and development of a race of wheat resist- ant to rust have been described (p. 355). The cultivation of races resistant to disease is very new work, but it promises to be the method by which we shall finally eliminate all the diseases of cultivated plants. 151. Suggestions for work. — Probably no work can be done with plant diseases except in learning to recognize some common diseases. As many cultivated plants as possible, including street trees, should be examined for diseases, especially for spotted leaves, wilts, galls, black knot, and cankers. All wild plants are subject to disease, and these might be used to extend the observations. In addition to this, specimens showing the usual diseases of the common cultivated plants can probably be obtained by any school from its state Agricultural Experiment Station. These will serve as valuable guides to the recognition of these diseases among the plants cultivated in the neighborhood of the school. 30 INDEX Heavy figures indicate pages on which illustrations occur. Acacia, flower of, 157. Adiantum, 90. Agave, 208. Agriculture, 296. Air-roots, 268j_269. Aleurone grains, 177. Alfalfa, 364. Alga?, 8. Alternation of generations, 75. Althaea, flower of, 137. Angiosperms, 115, 129. Annual rings, 239. Annuals, 238. Annular vessels, 238. Anther, 123, 134, 135, 136. Antheridium, 27 ; of ferns, 99 ; of liverworts, 74 ; of mosses, 80. Anthoceros, 83, 84, 85. Apple, 390; bitter rot of, 443, 444 ; canker on, tree, 442 ; flower of, 156; fruit of, 149; spot disease of, leaf, 434. Apricot, 393. Archegonium, of ferns, 98 ; of liverworts, 75 ; of mosses, 80. Ascomycetes, 57. Aspen, tree fungus on, 448. Aspidium, 92. Assimilation, 38, 176. Aster, 4(39, 490. Autumn colors, 214. • Axil, 226. B Bacteria, 43, 44. Bacteriology, 44. Bark, 240. Barley, 357, 358. Barley-production, map showing states of greatest, 357. Basidiomycetes, 58. Bast, 237. Bean, 167, 386; germination of, 177, 178, 179, 180, 181, 323, 324 ; section of, 319 ; seed-dis- charge, 168. Beet, 374; spot disease of, leaf, 438. Beggar-ticks, 173. Bilabiate, 134. Biology, 1. Bitter rot, 442. Black knot, 445. Bluebell, 133. Blue-green Algae, 31. Brown Algae, 31. Brown rot, 441. Bryophytes, 7, 66, 114. Bud, 225. Budding, 332. Bulb, 250, 377. Bulblet, 250. Burdock, 174. Cabbage, 373, 378, 379; black rot of, 447. Cactus, 209. Cactus deserts, 283. Calyx, 131. Cambium, 239. Cankers, 442. Canteloupe, 385. Capillary movement, 314. 455 456 INDEX Carbohydrate, 32, 35. Carbon dioxide, 32, 303. Carnation, 404, 405. Carnivorous plants, 218. Carpel, 120, 137. Carrot, 376. Catalpa, seed of, 171. Celery, 382. Cell, 9. Cellulose, 9. Cell-wall, 9. Cereals, 342. Chemistry of soil, 308. Cherry, 394. Chlorophycese, 31. Chlorophyll, 10, 33. Chloroplast, 10, 33. Chrysanthemum, 407. Cladophora, 16. Classification, 3. Climbers, 233. Clinging roots, 268. Clover, 363, 364. Club-mosses, 88, 91, 95, 101, 108. Cocklebur, 174. Coleochsete, 15. Colony, 12. Compass plants, 211. Conifers, 116. Cork cambium, 240. Corn, 137, 343, 344, 347, 348 349, 350 ; germination of, 182 section of a grain of, 318 ; selec- tion, 347 ; tester, 348. Corn-breeding, 337. Corn-production, map showing , states of greatest, 343. Corolla, 131. Cortex, 236. Cotton, 411, 412. Cotton-production, map showin; states of greatest, 414. Cotyledons, 126 ; escape of, 181 Cow-pea, 365. Cross-pollination, 158. Crown gall, 444. Cryptogams, 98. Cucumber, 384. Cultivated plants, 296. Currant, 400; black knot on, 446 ; spot disease of, leaf, 436. Cuticle, 205. buttings, 326, 327. iyanophycese, 31. Cycads, 117. Cyclic leaves, 229. iytoplasm, 10. Daffodil, 408. Dahlia, 254. Daisy, crown gall on, 445. Dandelion, fruit of, 169; root of, 253. Darlingtonia, 219. Deadnettle, 133. Deciduous forest, 286, 287. Deciduous habit, 214. Department of Agriculture, 333. Dicotyledons, 146. Digestion, 38, 176. Dionsea, 222. Diseases, 4, 41, 432 ; control of, 448. Disease-resistance, 335. Dogtooth violet, 153. Dormancy, 11. Dorsi ventral, 69. Dotted vessels, 238. Dros.era, 220, 221. Drought, 294. Drought-resistance, 336. Dunes, 282, 283. E Ectocarpus, 21, 26. Egg, 25. Elm, 228. Embryo, 318; of Angiosperms, 145 ; of Gymnosperms, 126. Embryo-sac, 142. Endosperm, 318; of Angio- INDEX 457 sperms, 167 ; of Gymnosperms, 127. Energy, 34. Epidermis, 69, 192, 205. Epigynous, 156. Epilobium, pollination of, 163. Epiphytes, 269. Equisetales, 102. Equisetum, 100, 101, 107. Evergreen habit, 215. Evolution, 4. Experiment Stations, 334. Fats, 177. Ferns, 88, 90, 92, 102, 103, 104, 105, 106, 107. Fertilization, 23 ; in Angio- sperms, 143 ; in Gymno- sperms, 125. Fibre plants, 411. Fig wort, pollination of, 162. Filament, 123, 134. Filicales, 104. Fireweed, seed of, 170. Flax, 414, 415. Flora, 8. Floriculture, 297, 401. Flowers, 130, 401 ; evolution of, 151. Food manufacture, 31. Food problem, 340. Food storage, 177. Foot, 76. Forage plants, 362. Forestry, 5, 419. Forests, care of, 422; character of, 420; and floods, 421; for- mation of, 421 ; products of, 424 ; protection of, 423 ; reser- vations, 427. Forest succession, 277. Fruit, 147, 383, 387. Fucus, 17, 26, 27, 28. Fungi, 40. Fungicides, 449. Funiculus, 141. Gametangium, 26. Gamete, 23. Gametophore, 77, 78, 79. Gametophytes, 76, 110, 111; of Angiosperms, 141 : of Ferns, 98 ; of Gymnosperms, 123, 124. Gardening, 368. Gemmae, 73. Geotropism, 179. Germination, 22 ; of seeds, 174. Germinator, seed, 321, 322, 324. Girdling, 240. Gloeothece, 12, 13. Gloeotrichia, 13, 14. Gooseberry, 400. Gourd family, 384. Grafting, 241, 330. 331, 332. Grape, 396 ; spot disease of, leaf, 439. Grape-fruit, 395. Grass family, 362. Green Algse, 31. Guard-cells, 193. Gymnosperms, 114, 115. H Habit, 224. Habitat, 273. Hairs, 206, 207. Haustoria, 46. Heart wood, 243. Heat, 301. Hemp, 416. Heredity, 5. Heterospory, 108. Homospory, 108. Horsetails, 102. Horticulture, 297. Host, 41. Houstonia, flower of, 164 ; pol- lination of, 163. Hybridization, 338. Hydrophytes, 279. Hydrotropism, 180. 458 INDEX Hypocotyl, 126, 185 ; escape of, 177. Hypogynous, 156. Infection, 449. Inorganic, 32. Insectivorous plants, 218. Insect-pollination, 158. Integument, 123. Internodes, 224, 326. Involucre, 380. Iris, flower of, 158 ; pollination of, 160. Irregularity, 133, 156. Irritability, 179. Jonquil, 408. Laminaria, 16. Layering, 232, 329. Leaf, 89, 187, 188; compound, 190 ; mosaic, 201, 202, 203 ; sec- tion of, 191 ; skeletonized, 189. Leaflet, 191. Leaves, as vegetables, 378. Legume family, 363. Legumes, 385. Lemon, 395. Lettuce, 380, 381. Lichens, 58, 59, 60, 61. Life of soil, 310. Life-relations, 5. Light, 301. Lily, anther of, 135. Limiting factors, 30Q. Linseed oil, 415. Liverworts, 67. Lycopodiales, 101. Lycopodium, 95. M Macrocystis, 16. Maple, fruit of, 170. Maple leaf, spot disease of, 435. Marchantia, 69, 70, 71, 73, 74, 75. Mass culture, 334. Meadows, 284, 285. Megasporangium, 108, 109. Megaspore, 108. Megasporophyll, 108, 109. Mesophyll, 194. Mesophytes, 279. Micropyle, 123. Microsporangium, 108, 109. Microspore, 108. Microsporophyll, 108, 109. Midrib, 189. Mildews, 437 ; downy, 47, 48, 49 ; powdery, 49, 50. Milkweed, seed of, 170. Molds, 46. Monocotyledons, 145. Mosses, 77. Motile leaves, 212, 213. Mucor, 45, 46, 47. Mushrooms, 53, 54, 55, 56, 57. Muskmelon, 384. Mycelium, 46. Mycorhiza, 64. N Narcissus, 408. Nectar, 159. Nepenthes, 219. Nereocystis, 17. Nitrogen, 303. Nodes, 224, 326. Nostoc, 12, 14. Nucellus, 123. Nucleus, 10. Nutrition, 2, 11. 0 Oak, 229. Oat-production, map showing states of greatest, 351. Oats, 351, 352, 353. INDEX 459 (Edogonium, 20, 21. Oils, 177. Onion, 377. Oogonium, 27. Oospore, 23. Orange, 394. Orchard fruits, 389. Orchards, 389. Orchid, flower of, 161 ; pollina- tion of, 161. Organic, 32. Oscillatoria, 13, 14. Osmosis, 264. Ovary, 138. Ovule, of Gymnosperms, 120, 122 ; of Angiosperms, 140. Oxygen, 300; as a by-product, 36. Palisade cells, 194, 206. Palmate, 189. Pansy, 405, 406. Parallel-veined, 189. Parasite, 40. Parsnip, 376. Peach, 148, 389, 392. Peach leaf curl, 445. Pear, 388, 391. Pear blight, 435. Peas, 386. Pedigree culture, 335. Peony, 131. Perennials, 238. Perianth, 130, 131. Perigynous, 156. Petal, 132. Petiole, 187. PhaeophycesB, 31. Phloem, 237. Phlox, 133. Phosphorus, 304. Photosynthesis, 34, 195. Phototropism, 183. Phycomycetes, 57. • Physics of soil, 309. Pine, 227. Pineapple, 149. Pine needles, 21^; section of, 215. Pinnate, 189. Pistil, 139. Pitcher-plants, 218, 219. Pith, 236. Pith rays, 237. Plains, 283. Plant associations, 272. yiant-breeding, 5, 164, 333. •Plant succession, 276. Plastid, 33. Pleurococcus, 12. Plum, 393 ; black knot on, 446. Plume, 126; escape, 181. Pods, of iris, 147 ; of sweet pea, 146. Pollen, 121. Pollen sac, 135. PoUen tube, 125. Pollination, 125 ; by insects, 158. Polypetalpus, 133. PoreUa, 72. Potato, 369, 370, 371; disease of, 440, 441 ; tuber, 328. Potentilla, 230; flower of, 156. Prairies, 284. Profile leaves, 211. Prop-roots, 265, 266, 267. Protective positions, 210. Protective structures, 204. Protein, 37. Protoplasm, 9. Protoplast, 9. Pteridophytes, 7, 88, 114. Pumpkin, 385. R Radish, 254, 372, 374. Rain, protection against, 209. Raspberry, 391, 399. Reaction, 185. Receptacle, 152. 460 INDEX Red Algse, 31. Reed swamp, 280. Regular, 133. Reproduction, 2, 11 ; in Algae, 17 ; in Liverworts, 73. Resistance, 452. Respiration, 36, 38, 175. Response, 178. Rhizoids, 71. Rhodophyceae, 31. Ribs, 189. Riccia, 68. Rice, 360, 362. Rice-production, map showing states of greatest, 361. Root, 94, 253, 372 ; development of, 180 ; structure of, 256. Root-cap, 255. Root-hairs, 256. Root-pressure, 244. Rootstock, 247, 248. Rose, 403, 404. Rosette-habit, 199, 200, 211. Rotation of crops, 363. Rust, 51, 52, 443. Rye, 359, 360. Rye-production, map showing states of greatest, 359. 8 Salts, movement of, in soil, 315.' Sap, ascent of, 242. Saprophyte, 40. Sap wood, 243. Sargassum, 18. Sarracenia, 218. Scales, 216. Seed, 126, 317; of Angiosperms, 147 ; box for germination of, 324 ; dispersal, 169 ; germina- tion of, 174, 320; of Gym- nosperms, 127; selection of, 319. Seed-firms, 333. Selaginella, 91, 108, 111. Self-pollination, 158. Senecio, fruit of, 169. Sensitive plant, 212. Sepal, 131. Sex, differentiation of, 25 ; ori- gin of, 23. Sex-organs, 26. Shading, projection against, 199.. Shasta daisy, 403. Sieve vessels, 238. Smilax, 225. Snapdragon, 133. Snowflake, 157. Soil, 259, 298, 308. Soil fungi, 61. Sorus, 96, 97, 98. Spanish needles, 173. Spermatophytes, 7, 114, 129. Sperms, 25 ; of Cycads, 125. Spiral leaves, 228. Spiral vessels, 237. Spirogyra, 27, 29. Spongy tissue, 194. Sporangium, 22 ; of Ferns, 96, 97. Spore, 21. Sporophore, 47. Sporophyll, 97. Sporophyte, 76, 81, 83; of Angiosperms, 130 ; of Gym- nosperms, 118. Spot diseases, 434, 435, 436, 437, 438, 439. Squash, 385. Stamen, 121, 123; of Angio- sperms, 134. Stem, 93, 224 ; structure of, 235. Stigma, 138. Stimulus, 178. Stomata, 192, 193. Stone-fruit diseases, 441. Storage form, 36. Strawberry, 391, 398; spot dis- ease of, leaves, 437. Strawberry-plant, 231. Street trees, 428 ; care of, 430. Strobilus, 104 ; of Gymno- sperms, 118, 119, 120, 121, 122. INDEX 461 Style, 138. Substratum, 69. Subterranean stems, 245. Summaries, Algae, 30 ; Angio- sperms, 148 ; Bryophytes, 87 ; dispersal and germination of seeds, 185 ; the flower and insect-pollination, 165 ; food- manufacture, 39 ; Fungi, 64 ; Gymnosperms, 128 ; leaves, 222 ; plant associations, 289 ; Pteridophytes, 112; roots, 269 ; stems, 251. Sundew, 220, 221. Surgery, 451. Swamp forest, 281. Sweet corn, 350. Sweet pea, 406; pollination of, 160. Sweet potato, 375, 376. Sympetalous, 133, 154. Tap-root, 255. Tendrils, 216, 217, 246. Testa, 127, 167, 317. Thallophytes, 6, 8, 40, 114. Thorns, 217, 245. Tillage, 312. Toadflax, 133. Tobacco, flower of, 132. Tomato, 383. Toxic substances, 305. Tracheary vesselsi237. Transfer form, 36. Transpiration, 195. Tropical forest, 288. Tube nucleus, 141. Tuber, 249, 369; potato, 328. Tulip, 409. Tumbleweed, 172. Turgor, 10. Turnips, 373, 374. U Ulothrix, 15, 16, 21, 23. Vascular bundles, 237. Vascular cylinder, 93, 94, 236. Vascular system, 89. Vaucheria, 27, 28. Vegetables, 367. Vegetative multiplication, 18. Vegetative propagation, 326. Veins, 90, 195. Venus fly-trap, 222. Viability, 318. Violet, 405 ; seed of a, 317 ; seed- discharge, 168. W Water, 302 ; movement of, in soil, 314. Watermelon, 385. Water roots, 266. Water storage, 208. Wheat, 354, 355, 356. Wheat-production, map show- ing states of greatest, 364. Wheat rust, 51, 52. Wild wheat, 355. Wilts, 446. Wood, 237. Woodbine, 234, 235. X Xerophytes, 279. Xylem, 89, 237. NATURE STUDY AND AGRICULTURE Practical Nature Study and Elementary Agriculture A Manual for the Use of Teachers and Normal Students. By JOHN M. COULTER, Director of the Department of Botany, University of Chicago; JOHN G. COULTER^ Professor of Biology, Illinois State Normal University ; ALICE JEAN PATTERSON, Department of Biology, in charge of Nature Study, Illinois State Normal University. 1 2 mo, cloth, $1.35 net. This book is an attempt, on very practical lines, to help the teacher of nature study to become more independent in his work, and to make his work more definite. The volume has grown out of the experience of the authors. The material has largely been used in regular class work, and found efficient under conditions similar to those of the average school. _______ Part I is devoted to presenting the principles of nature study, its mission and spirit, as well as the dangers which the study entails and how to avoid them. It is practically a guide to the teaching of nature study. Part. II contains a detailed topical outline by grades and seasons of the materials used in nature study in the training school at the Illinois State Normal University. Its definite outlines of work will be of important service to teachers who are called upon to handle the subject with slight previous training. Part III is principally devoted to an outline course for elementary agriculture in the seventh and eighth grades, with most of the lessons worked out in detail. These lessons have all satisfactorily met the test of class-room use. Part IV comprises certain chapters on more general topics — material which will prove serviceable for teachers whose general science training has been slight or is lacking entirely. The aim is to provide a scientific point of view of the materials arid principles which are to be used in the work. The study of this exceedingly practical book, the aim of which is to aid in making nature study practical under present teaching conditions, should produce better teachers and more enlightened students. D. APPLETON AND COMPANY NEW YORK CHICAGO 441e ~^^~""""~~~ ~~~""~~~ ~~"" " CHEMISTRY FROM A NEW STANDPOINT An Inductive Chemistry By ROBERT H. BRADBURY, A.M., Ph.D., Head of the Department of Science, Southern High School, Philadelphia. I2mo, Cloth, $1.25. This is a complete, modern text, practical and teachable, for high-school students. The subject is developed along lines adapted to the pupil's equipment. Both method and order of presentation are par- ticularly sound. Constant appeal is made to the experience of the student's everyday life, and new material is introduced in logical order, according to the interest and natural com- prehension of the student. The text is eminently modern in spirit, as to subject matter. Recent developments of the first importance, absent in other texts, are simply but adequately treated here. Emphasis is likewise laid on the method of reasoning followed in attaining results as well as on the mere facts of the science. The book is unusually teachable, in many ways. It intro- duces the history of the subject to the best advantage. It contains helpful classifications, in the form of tables, and lists of definitions. The illustrations, too, are unusually clear and relevant. The Syllabus and Entrance Examination requirements have been thoroughly covered. The fact that these required topics are printed in bold-faced type in the index, will be of great assistance to teachers and students. D. APPLETON AND COMPANY NEW YORK CHICAGO 501e TWENTIETH CENTURY TEXT-BOOKS A High School Course in Physics By FREDERICK R. .GORTON, Ph.D., Associate Professor of Physics, Michigan State Normal College. Fully and Practically Illustrated. I2mo, Cloth, $1.25 net. The author has written a text-book in Physics which is above all things practical, from the point of view of both teacher and pupil. All scientific facts are clearly stated and referred, wherever such reference will be valuable, to the student's own experience and to the ordinary phenomena of his everyday observation. Without sacrificing the essentially scientific nature of the subject the author recognizes it as a science which has a very definite bearing upon everyday life. The author believes that the class-room work should be accompanied by suitable laboratory experimentation by the pupils supplemented with demonstrative experiments by the instructor. Stress is laid upon the beneficial results to which the study of Physics has led as its development has progressed. Espe- cial attention has been given to the interesting historical development of the subject. Portraits and adequate bio- graphical sketches of many scientists to whom the discovery of great principles is due have been inserted. The problems throughout the book eliminate the usual exercises in pure reduction and substitute those of a more concrete and practical nature. The apparatus described is as simple as experience has shown to be consistent with satisfactory results. The illustrations are abundant and each is given a descrip- tive legend. To aid the pupil in reviewing and the teacher in quizzing, there are summaries at the ends of the chapters. No subject has been left out that is called for in the report of the College Entrance Requirement Board. D. APPLETON AND COMPANY NEW YORK CHICAGO TWENTIETH CENTURY TEXT-BOOKS. An Introduction to Physical Geography. By GROVE KARL GILBERT, LL. D., United States Geological Sur- vey ; Author of "The Geology of the Henry Mountains," "Lake Bonneville," Numerous Reports, etc., in publications of United States Geological Survey ; and ALBERT PERRY BRIGHAM, A. M., Professor of Geology, Colgate University, Hamilton, N. Y., Fellow of the Geological Society of America, etc., Associate Editor Bulletin American Geographical Society, Author of " A Text-Book of Geology " (Twentieth Century Text-Books). Illustrated. I2mo. Cloth, $1.25. SIX SALIENT POINTS. The new pedagogy of Physical Geography receives in this book its first adequate presentation. Hence, this text meets the present requirements of high school and college-entrance work perfectly and in full detail. Treatment adapted to the early years of the course — the book will interest pupils aged fourteen. Statements throughout are not "merely theoretical, but definitely concrete, appropriately illustrated, and logically summarized. Topics cover "The Physical Environment of Man:" The Earth as a Globe, the Ocean, the Air, and the Land— in increasing proportion. ' The exquisite half-tone illustrations far surpass in beauty, helpfulness, and number anything before attempted. A most important and significant feature. THE IDEAL COURSE AND GILBERT AND BRIGHAM'S BOOK. This book meets fully, in minute detail, and for the first time, all the specifications set forth in the Report of the Committee on College Entrance Requirements to the National Educational Association in 1899. It keeps accurately to the definition laid down ; it furnishes the requisite kind and amount of instruction to train the observation and to prepare for later special courses in science ; and it elevates physical geography beyond cavil to the proper plane for a college-entrance requirement, by organizing its content to its highest capacity as a pedagogic discipline. D. APPLETON AND COMPANY, NEW YORK. An Elementary Commercial Geography. By CYRUS C. ADAMS, B.A., F.A.G.S., Presi- dent of The American Geographical Society ; Author of "A Text-Book of Commercial Geography " (Twentieth Century Text-Books). 1 2 mo. Cloth, $1.10. There are obvious reasons for teaching elementary commercial geography in grammar schools. 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It brings out the commercial powers of the United States in a way that is entirely within the realization and intelligence of the grammar-school maturity. D. APPLETON AND COMPANY, NEW YORK. BOSTON. CHICAGO. LONDON. 2??e ANCIENT HISTORY FOR THE HIGH SCHOOL The Story of the Ancient Nations By WILLIAM L. WESTERMANN, Associate Pro- fessor in History, University of Wisconsin. Illus- trated. 1 2 mo, Cloth, $1.50. There is no other branch of history taught in our High Schools in which so much new material has come to light during recent years as in ancient history. Much of the best source material is not available, in translated form, to the teacher. This text-book has been written with the desire to put into the hands of High School teachers and pupils, in simple and concrete form, the story of the development of ancient civilization as it appears in the light of the historical material recently discovered. It is the outcome of more than a decade of teaching, both in High School and University classes. The attempt has been made to present the progress of ancient civilization as a continuous and unified process. There has been included, in simple terms, as much of the business and social background as space would permit. The language of the book is clear and succinct. The order of presentation is logical, and the correlation of facts exact. There are exceedingly helpful and well-written generaliza- tions, giving the significance of the various periods. There are plentiful maps throughout the book. The illus- trations, with the exception of a few carefully selected restora- tions, are almost entirely drawn from ancient sources. They have been carefully chosen for the light which they throw on the life of the people. D. APPLETON AND COMPANY NEW YORK CHICAGO 504e THE FOURTH SEVENTH DAY OCT 31 1932 * FEB 6 1939 jyt 861958 2l-3m-6,'32 UNIVERSITY OF CALIFORNIA LIBRARY 11 m M 1 •! !;1 I! ill n I