E1OLOGY LIBRARY G A PRACTICAL COURSE IN BOTANY WITH ESPECIAL REFERENCE TO ITS BEARINGS ON AGRICULTURE, ECONOMICS, AND SANITATION BY E. F. ANDREWS WITH EDITORIAL REVISION BY FRANCIS E. LLOYD PROFESSOR OF BOTANY, ALABAMA POLYTECHNIC INSTITUTE NEW YORK •:• CINCINNATI •:• CHICAGO AMERICAN BOOK COMPANY BIOLOGY LIBRARY G COPYRIGHT, 1911, BY E. F. ANDKEWS. ENTERED AT STATIONERS' HALL, LONDON. ANDKEWS'8 PR. BOTANY. W.P.I PREFACE IN preparing the present volume, the aim of the writer has been to meet all the college entrance requirements and at the same time to bring the study of botany into closer touch with the practical business of life by stressing its relations with agriculture, economics, and, in certain of its aspects, with sani- tation. While technical language has been avoided so far as the requirements of scientific accuracy will permit, the student is not encouraged to shirk the use of necessary botani- cal terms, out of a mere superstitious fear of words because they happen to be a little new or unfamiliar. Such a practice not only leads to careless and inaccurate modes of expression, but tends to foster a slovenly habit of mind, and in the long run causes the waste of more time and labor in the search after roundabout, and often misleading, substitutes, than it would require to master the proper use of a few new words and phrases. In the choice of materials for experiment and illustration, the endeavor has been to call for such only as are familiar and easily obtained. The specimens for flower dissection have been selected mainly from common cultivated kinds, because their wide distribution makes them easy to obtain everywhere, while in cities and large towns they are practically the only specimens available. Another important consideration has been the desire to spare our native wild flowers, or at least not to hasten the extinction with which they are threatened by the ravages of Sun- day excursionists and summer tourists, to whose unthinking, but none the less destructive, incursions, the automobile has laid open the most secret haunts of nature. The influence of the public school teacher, and more especially the teacher of botany, is the most potent factor from which we can hope for aid in putting a stop to the relentless persecution that has practically exterminated many of our choicest wild plants and is fast iii 226071 iv PREFACE reducing the civilized world to a depressing monotony of weediness and artificiality. Except for purely systematic and anatomical work, flowers can be studied to better purpose in their living, active state than as dead subjects for dissection ; and the best way to show our interest in them, or to get the most rational enjoyment out of them, is not, as a general thing, to cut their heads off and throw them away to wither and die by the roadside. The teacher, by instilling into the minds of the rising generation a reverence for plant life, may do a great deal to aid in the conservation of one of our chief national assets for the gratification of the higher esthetic instincts. The fruits and flowers of cultivation do not stand in the same need of pro- tection, since they are produced solely with a view to the use and pleasure of man, and their propagation is provided for to meet all his demands. To avoid too frequent interruptions of the subject matter, the experiments are grouped together at the beginning or end of the sections to which they belong, according as they are intended to explain what is coming, or to illustrate what has gone before. A few exceptions are made in cases where the experiment is such an integral part of the subject that it would be meaningless if separated from the context. Under no circumstances should those capable of being performed in the schoolroom be omitted, as much of the information which the book is intended to give is conveyed by their means. For this reason, and also because the aim of the book is to present the science from a practical rather than from an academic point of view, the experiments outlined are for the most part of a simple, practical nature, such as can be performed by the pupils them- selves with a moderate expenditure of ingenuity and money. The experience of the writer has been that for the average boy or girl who wishes to get a good general knowledge of the subject, but does not propose to become a specialist in botany, the best results are often obtained by the use of the simplest and most familiar appliances, as in this way attention is not distracted from the experiment itself to the unfamiliar appa- ratus for making it. In saying this, it is not meant to under- PREFACE V rate the value of a complete laboratory equipment, but merely to emphasize the fact that the lack of it, while a disadvantage, need not be an insuperable bar to the successful teaching of botany. It is, of course, taken for granted that in schools pro- vided with a suitable laboratory outfit, teachers will be pre- pared to supplement or to replace the exercises here outlined with such others as in their judgment the subject may demand. There are as many ideals in teaching as 'there are teachers, and the most that a textbook can do is to present a working model which every teacher is free to modify in accordance with his or her own method. The writer takes pleasure in acknowledging here the many obligations due to Professor Francis E. Lloyd, of the Botanical Department of the Alabama Polytechnic Institute, at Auburn, Ala., for his valuable aid in the revision of the manuscript, for the highly interesting series of illustrations relating to photo- tropic movements, and for advice and information on points demanding expert knowledge which have contributed very ma- terially to whatever merit this volume may possess. Other members of the Auburn faculty to whom the author feels especially indebted are Mr. C. S. Ridge wa}% assistant in the Botanical Department, Professor J. E. Duggar, of the Agricul- tural Department, and Dr. B. B. Ross and Professor C. W. Williamson of the Department of Chemistry. Acknowledg- ments are due also to Professor George Wood of the Boys' High School, Brooklyn, for suggestions which have been of great assistance in the preparation of this work ; to Professor W. R. Dodson, of the University of Louisiana, for illustrative material furnished, and to Professor William Trelease for the loan of original material used in reproducing the beautiful cuts from the Reports of the Missouri Botanical Garden, credit for which is given in the proper place. E. F. ANDREWS. AUBURN, ALABAMA. FULL-PAGE ILLUSTRATIONS PLATE PA.GR 1. A GROVE OF LIVE OAKS NEAR SAVANNAH, GEORGIA . Frontispiece 2. CARRYING WATER OVER THE MISSISSIPPI LEVEE BY SIPHON TO IRRIGATE RICE FIKLDS ........ 8 3. AERIAL ROOTS OF A MEXICAN STRANGLING FIG ... 73 4. A FOREST OF BAMBOO 99 5. A GROUP OF CONIFERS 108 6. A WHITE OAK, SHOWING THE GREAT SPREAD OF BRANCHES • 117 7. A TIMBER TREE SPOILED BY STANDING TOO MUCH ALONE . 125 8. AN AMERICAN ELM, ILLUSTRATING DELIQUESCENT GROWTH . 130 9. VEGETATION OF A MOIST, SHADY RAVINE ..... 151 10. A MOSAIC OF MOONSEED LEAVES ....... 179 11. HYBRID BETWEEN A RED AND A WHITE CARNATION . . . 227 12. GOOSEBERRIES, SHOWING IMPROVEMENT BY SELECTION . . 251 13. THE EFFECTS OF IRRIGATION 272 14. A XEROPHYTE FORMATION OF YUCCAS AND SWITCH PLANTS . 282 15. A GIANT TULIP TREE OF THE SOUTH ATLANTIC FOREST REGION 293 CONTENTS CHAPTER I. THE SEED PAGE I. THE STORAGE OF FOOD IN SEEDS 1 II. SOME PHYSIOLOGICAL PROPERTIES OF SEEDS .... 10 III. TYPES OF SEEDS '. ... 12 IV. SEED DISPERSAL .......... 21 FIELD WORK 28 CHAPTER II. GERMINATION AND GROWTH I. PROCESSES ACCOMPANYING GERMINATION 29 II. CONDITIONS OF GERMINATION 33 III. DEVELOPMENT OF THE SEEDLING 40 IV. GROWTH 47 FIELD WORK 52 CHAPTER III. THE ROOT I. OSMOSIS AND THE ACTION OF THE CELL ..... 53 II. MINERAL NUTRIMENTS ABSORBED BY PLANTS^ ... 58 III. STRUCTURE OF THE ROOT 61 IV. THE WORK OF ROOTS 65 V. DIFFERENT FORMS OF ROOTS" 72 FIELD WORK 80 CHAPTER IV. THE STEM I. FORMS AND GROWTH OF STEMS 81 II. MODIFICATIONS OF THE STEM 88 III. STEM STRUCTURE A. MONOCOTYLS 96 B. HERBACEOUS DICOTYLS 102 C. WOODY STEMMED DICOTYLS ..,,.. J07 vu viii CONTENTS PAGE IV. THE WORK OF STEMS 112 V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES . 118 VI. FORESTRY 124 FIELD WORK 128 CHAPTER V. BUDS AND BRANCHES I. MODES OF BRANCHING 131 II. BUDS 138 III. THE BRANCHING OF FLOWER STEMS 141 FIELD WORK 145 CHAPTER VI. THE LEAF I. THE TYPICAL LEAF AND ITS PARTS 147 II. THK VEINING AND LOBING OF LEAVES 154 III. TRANSPIRATION 160 IV. ANATOMY OF THE LEAF ........ 164 V. FOOD MAKING . . .168 VI. THE LEAF AN ORGAN OF RESPIRATION 174 VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL RELATIONS . 177 VIII. MODIFIED LEAVES ......... 189 FIELD WORK .194 CHAPTER VII. THE FLOWER I. DISSECTION OF TYPES WITH SUPERIOR OVARY . . . 196 II. DISSECTION OF TYPES WITH INFERIOR OVARY . . . 204 III. STUDY OF A COMPOSITE FLOWER 210 IV. SPECIALIZED FLOWERS 214 V. FUNCTION AND WORK OF THE FLOWER 219 VI. HYBRIDIZATION . 223 VII. PLANT BREEDING 230 VIII. ECOLOGY OF THE FLOWER A. THE PREVENTION OF SELF-POLLINATION . . . 235 B. WIND POLLINATION 239 C. INSECT POLLINATION ....... 241 D. PROTECTIVE ADAPTATION ...... 245 FIELD WORK 249 CONTENTS ix CHAPTER VIII. FRUITS PAGE I. HORTICULTURAL AND BOTANICAL FRUITS .... 250 II. FLESHY FRUITS 255 III. DRY FRUITS 260 IV. ACCESSORY, AGGREGATE, AND MULTIPLE FRUITS . . . 265 FIELD WORK 269 CHAPTER IX. THE RESPONSE OF THE PLANT TO ITS SURROUNDINGS I. ECOLOGICAL FACTORS 271 II. PLANT ASSOCIATIONS 277 III. ZONES OF VEGETATION 288 FIELD WORK 294 CHAPTER X. CRYPTOGAMS I. THEIR PLACE IN NATURE . 296 II. ALG*: 299 III. FUNGI 303 A. BACTERIA 306 B. YEASTS 314 C. RUSTS 317 D. MUSHROOMS 323 IV. LICHENS 329 V. LIVERWORTS .......... 334 VI. MOSSES 341 VII. FERN PLANTS 344 VIII. THE RELATION BETWEEN CRYPTOGAMS AND SEED PLANTS . 354 IX. THE COURSE OF PLANT EVOLUTION 359 FIELD WORK 362 APPENDIX 1. SYSTEMATIC BOTANY . . 364 2. WEIGHTS, MEASURES, AND TEMPERATURES 367 CHAPTER I. THE SEED I. THE STORAGE OF FOOD IN SEEDS MATERIAL. — In addition to the four food tests described in Exps. 1-6, there should be provided some raw starch, a solution of grape sugar, the white of a hard-boiled egg, and any fatty substance, such as lard or oil. For Exps. 8 and 9, a little diastase solution will be nec- essary. "Taka" diastase, made from rice acted upon by a fungus, can be obtained for a trifle at almost any drug store. LIVING MATERIAL. — Grains of corn and wheat, and seeds of some kind of bean, the larger the better. The "horse bean" (Vicia faba), if it can be obtained, makes an excellent object for study, as the cells are so large that they can be seen with the naked eye. For showing the presence of proteins (aleurone grains) and oily matter, use thin cross sec- tions through the kernel of a castor bean or a Brazil nut. Specimens for the study of the individual cell will be found in the hairs growing on squash seedlings, in the epidermis of one of the inner coats of an onion, in the roots of oat or radish seedlings, or in the section of a young corn root. A compound microscope will be required for this study. i. The economic importance of seeds. — As a source of food to both man and the lower animals, the importance of seeds can hardly be overrated. All the flour, meal, rice, hominy, and other breadstuffs sold in the market come from them, to say nothing of the fleece from the cotton seed that clothes the greater part of the world, besides furnishing a substitute for lard and an important food for cattle. The oils and fats stored in nuts are also to be taken into account, the peanut alone yielding the greater part of the so-called olive oil of commerce. Since the value of our farm crops depends largely upon the kind and quantity of these sub- stances furnished by them, it is worth our while, as a matter of economic as well as scientific interest, to learn something about the nature of the different foods contained in plants. 1 PRACTICAL COURSE IN BOTANY cba 1 2 FIGS. 1-3. — The world's three most important food grains (magnified) : 1, sec- tion of a rice grain ; a, cuticle ; b, aleurone, or protein layer ; c, starch cells ; d, germ ; 2, section of a wheat grain ; k, germ ; s, starch ; a, gluten ; t, t, t, layers of the seed coat ; 3, section of a grain of corn ; c, husk ; e, aleurone layer containing proteins ; eg, yellowish, horny endosperm, containing proteins and starch ; ew, lighter starchy endosperm : the darker part below is rich in oil and proteins, and contains the em- bryo, consisting of the absorbing organ, or cotyledon, sc; the rudimentary bud, s ; and the root, w. (1, from Circular 77, La. Exp. Station ; 2, from France ; 3, from Sachs.) 2. Why food is stored in seeds. --The one purpose for which plants produce their seed is to give rise to a new generation and so carry on the life of the species. The seed is the nursery, so to speak, in which the germ destined to produce a new plant is sheltered until it is ready to begin an inde- pendent existence. But the young plant, like the young animal, is incapable of providing for itself at first, and would die unless it re- ceived nourishment from the mother plant until it has formed roots and leaves so that it FIGS. 4-7. — Sections of corn grains showing different qualities of food contents : 4, 5, small germ and large proportion of horny part, show- ing high protein ; 6, 7, large germ and smaller pro- portion of horny part, showing high oil content. SO manufacture food can for THE SEED itself. Plants in general require very much the same food that animals do, and they have the power, which animals have not, of manufacturing it out of the crude materials con- tained in the soil water and in the air. Such of these foods as are not needed for immediate consumption, they store up to serve as a provision for the young shoot when the seed begins to germinate. 3. Food substances contained in seeds. — There are four principal nutriments stored in seeds: sugars, starches, oils, and proteins. The first are held in solution and can be detected, if in sufficient quantity, by the taste. The most important varieties of this group are cane and grape sugar, the latter occurring most abundantly in fruits, the former in roots and stems. Oil usually appears in the form of globules. It is very abundant in seeds of the flax, castor bean, and Brazil nut. In the corn grain it is found in the part constitut- ing the germ, or embryo (Figs. 6, 7). Starches and proteins occur in the form of small granules, which have specific shapes in different plants (Figs. 8, 9). Those containing pro- teins are called ateurone grains, and are, as a rule, smaller than the starch grains with which they are intermixed in the bean and some other seeds. In wheat, corn, rice, and most grains they form a layer just inside the husk, as shown in Fig. 10. This is the reason why polished rice and finely bolted flour are less nu- tritious than the darker kinds, from which this valuable food substance has not been removed. The two most familiar kinds of proteins are the albumins, of which the white of an egg is a well-known example, and the glutins, which give to the dough of wheat flour and oatmeal their peculiar gummy or " glutinous " structure. FIGS. 8-9. — Different forms of starch grains : 8, rice ; 9, wheat. PRACTICAL COURSE IN BOTANY FIG. 10. — Transverse section hear the outside of a wheat grain : e, the husk ; a, cells containing protein granules ; s, starch cells (after Tschirch). 4. Organic foods. - - These four substances, starch, sugar, fats, and proteins, with some others of less frequent oc- currence, are called organic foods, because they are pro- duced, in a state of nature, only through the action of organized living bodies, or, _________ more strictly speaking, of US living vegetable bodies. 5. Our dependence upon plants. — While the animal organism can digest and assimilate these substances after they have been formed by plants, it has no power to manufacture them for itself, and, so far as we know at present, is wholly depend- ent upon the vegetable world for these necessaries of life. In one sense the whole animal kingdom may be said to be parasitic on plants. The wolf that eats a lamb is getting his food indirectly from the grains and grasses consumed by its victim, and the lion that devours the wolf that ate the lamb is only one step further removed from a vegetable diet. 6. The vegetable cell. — If you will break open a well- soaked horse bean and examine the contents with a lens, you will see that they are composed of small oval or roundish granules packed together like stones in a piece of masonry. These little bodies, called cells, are the ultimate units out of which all animal and vegetable structures are built up, as a wall is built of bricks and stones. They differ very much from bricks and stones, however, in that they are, or have been, living structures with their periods of growth, activity, decline, and death, just like other living matter, as will be seen by and by, when we come to look more particularly into their life history. They consist usually of an inclos- THE SEED 5 ing membrane which contains a living substance called protoplasm. This is the essential part of the cell, and, so far as we know at present, the physical basis of all life. Cells are commonly more or less rounded in shape, though they take different forms according to the purpose they serve. Sometimes, as in the fibers of cotton and the down of young leaves, they are long and hairlike; when closely packed, they often become angular by pressure, like those shown in Figs. 10, 11. The cells composing the thick body of the bean are for the most part starch and other substances stored up for food, which render observation difficult. It will, therefore, be better to choose for a study of the indi- vidual cell some kind that will show the essential parts more distinctly. 7. Microscopic examination of a cell. — Place under a high power of the microscope a portion of fresh skin from one of the inside scales of an onion, or a piece of the root tip of a very young corn or oat seedling, and fix your attention on one of the individual cells. Notice (1) the cell wall or inclosing membrane, w (Fig. 11) ; (2) the protoplasm, p, which may be recognized by its granular appearance ; (3) the nucleus, n] and (4) the cell sap, s. In very young cells the protoplasm will be seen to fill most of the interior; but FlG 1 1_Typical cells. in mature ones, like the large one on the n> nucleus ; p, protoplasm ; • v , r .-•_ r> •, f ,1 • T • w, cell wall; s, sap. right of the figure, it forms a thin lining around the wall, with the nucleus on one side, while the cell sap, composed of various substances in solution, occupies the central portion. Though there is generally an inclosing wall, this is not essential, its office being to give strength and me- chanical support by holding the contents together, as an India-rubber bag holds water. It is the turgidity of the cell, when distended with liquid, that gives firmness to herba- ceous plants and the tender parts of woody ones. This 6 PRACTICAL COURSE IN BOTANY may be illustrated by observing the difference between a rubber bag when quite full and when only half full of water, or a football when partially and when fully inflated. In its simplest form, however, the cell is a mere particle of protoplasm, which has one part, constituting the nucleus, a little more dense in appearance than the rest, but this kind is not common in vegetable structures. 8. How food substances get into the cells. — As there are no openings in the cell walls, the only way substances can get into a cell or out of it is by soaking through the inclosing membrane, as will be explained in a later chapter. Since starch, oil, and proteins, the most important foods stored in seeds, are none of them soluble in the cell sap, it is clear that they could not have got into the cells in their present state, but must have undergone some change by which they were rendered capable of passing through the cell wall. 9. Digestion. - - The process by which this change is brought about is known as digestion, from its similarity to the same function in animals. Not only are foods, in the state in which we find them stored in the seed, incapable of passing through the cell wall, but the protoplasm, the living part of the cell, has no power to assimilate and to utilize these substances as food until they have been re- duced to a soluble form in which they can be diffused freely from cell to cell through any part of the plant. By diffusion is meant the gradual spread of soluble substances through the containing medium, as when a lump of sugar or salt, dropped into a glass of water, dissolves and slowly diffuses through the contents, imparting a sweet or salty taste to the whole. During the process of digestion the different kinds of food are acted upon and made soluble by certain chemical ferments, which are secreted in plants for the purpose. The digestion of starch, the most abundant of plant foods, is effected by diastase, a common ferment obtained from ger- THE SEED M. minating grains of barley, wheat, corn, rice, etc. By the presence of diastase starch is converted into grape sugar, a substance which is readily soluble in water, and which can be diffused easily through the tissues of the plant to any part where it is needed. In this way food travels from the leaf, where it is made, to the seed, where the sugar is generally reconverted into starch and stored up for future use, though some- times, as in the sugar corn and sugar pea, it remains in part unchanged. The kernels of this kind of corn can be distinguished readily from those of the ordinary starch corn, after maturity, by their wrinkled appear- ance, owing to their greater loss of water in drying. 10. Food tests. — In or- der to tell whether any of the food substances named occur in the seeds that we are going to examine, it will be necessary to understand a few simple tests by which their presence may be recognized. The chemicals required can be ordered ready for use from a druggist or may be prepared in the laboratory as needed, according to the directions given. Write in your notebook a brief account of each ex- periment made, with the conclusions drawn from it. EXPERIMENT 1 . To DETECT THE PRESENCE OF FATS. — Rub a small lump of butter or a drop of oil on a piece of thin white paper. What is the effect ? EXPERIMENT 2. ANOTHER TEST FOR FATS. — Place some macerated alcanna root in a vessel with alcohol enough to cover it, and leave for an hour. Add an equal bulk of water and filter. The solution will stain fats, oils, and resins deep red. FIG. 12. — Starch grains of wheat in different stages of disintegration under the action of a ferment (diastase), accompany- ing germination : a, slightly corroded ; b, c, and d, more advanced stages of decomposi- tion. 8 PRACTICAL COURSE IN BOTANY THE SEED 9 EXPERIMENT 3. To SHOW THE PRESENCE OF STARCH. — Put a drop of iodine solution on some starch. What change of color takes place ? To make iodine solution, add to one part of iodine crystals 4 parts potas- sium iodide and 95 parts water. It should be kept in the dark, as light decomposes it. Iodine colors starch blue, protein substances light brown. In testing for starch, the solution should be diluted till it is of a pale color, otherwise the stain will be so deep as to appear black. EXPERIMENT 4. A TEST FOR PROTEINS. — Place a small quantity of the white of an egg, diluted with water, in a clean glass and add a few drops of nitric acid ; or drop some of the acid on the white of a hard- boiled egg. What is the effect ? Nitric acid turns proteins yellow ; if the color is indistinct, add a drop of ammonia, when an orange color will ensue. EXPERIMENT 5. ANOTHER TEST FOR PROTEINS. — Place on the sub- stance to be examined a drop of a saturated solution of cane sugar and water ; add a drop of pure sulphuric acid ; if proteins are present, they will be colored red. See also Exp. 3. EXPERIMENT 6. A TEST FOR GRAPE SUGAR. — Heat a teaspoonful of Fehling's Solution to the boiling point in a test tube (a common glass vial can be used by heating gradually in water) and pour in a few drops of grape sugar solution. Heat again and observe the color of the precipitate that forms. Fehling's Solution may be obtained of the druggist, or, if preferred, it may be prepared in the laboratory as follows : (a) Dissolve 173 grams of crystallized Rochelle salts and 125 grams of caustic potash in 500 cc. of water; (6) dissolve 34.64 grams crystallized copper sulphate in 500 cc. of water, and mix equal parts as needed. (For English equivalents, see Appendix, Weights and Measures.) The two mixtures must be kept sep- arate till wanted for use, or prepared fresh as needed. Grape Sugar causes Fehling's Solution to form a red precipitate. EXPERIMENT 7. To SHOW THE DIFFERENCE BETWEEN SUGAR AND STARCH IN REGARD TO SOLUBILITY. — Mix some sugar with water and notice how readily it dissolves. Try the same experiment with starch and observe its different behavior. EXPERIMENT 8. To SHOW HOW STARCH is DISINTEGRATED IN THE ACT OF DIGESTION. — Place a few grains of starch on a slide, add a drop or two of diastase solution, and observe under the microscope ; the starch granules will be seen to disintegrate and melt away. Even with a hand lens it can be seen, from the greater clearness of the liquid in comparison with a mixture of untreated starch and water, that the grains have been dissolved. 10 PRACTICAL COURSE IN BOTANY EXPERIMENT 9. To SHOW THAT DIASTASE CONVERTS STARCH INTO SUGAR. — Make a paste of boiled starch so thin that it looks like water. Pour a small quantity of it into each of two tubes, adding a little diastase to one and leaving the other untreated. Keep in a warm place for twenty- four hours, then test both tubes for starch, as directed in Exp. 3, and note the result. If the diastase has not acted, add a little more and watch. Practical Questions 1. Name all the food and other economic products you can think of that are derived from the seed of maize; from wheat; from flaxseed; from cotton. 2. Mention some seeds from which medicines are procured. 3. Name all the seeds you can think of from which oil is obtained ; starch; some that are rich in proteins. (Exps. 1-5.) 4. Describe some of the ways in which these products are frequently adulterated. 5. If you were raising corn to sell to a starch factory, what part of the seed would you seek to develop ? If to feed stock, what part ? Why, in each case? (3; Figs. 4-7.) 6. What grain feeds more human beings than does any other ? 7. Name all the seeds you can think of that contain sugar in sufficient quantity to be detected without chemical tests ; that is, by tasting alone. 8. Is " coal oil" a mineral or an organic substance? Explain, by giving an account of its origin. 9. What is gluten ? (3.) Name some grains that are especially rich in it. 10. Which of our three chief food grains is a water plant ? (See Plate 2.) Which grows farthest south ? Which farthest north ? Which one is of American origin ? II. SOME PHYSIOLOGICAL PROPERTIES OF SEEDS MATERIAL. — Seeds of squash, pumpkin, or other melon ; castor bean ; any kind of common kidney bean ; grains of Indian corn. APPLIANCES. — In the absence of gas, an alcohol or kerosene lamp may be used for heating. A double boiler can easily be made by using two tin vessels of different sizes. Partly fill the larger one with water, set in it the smaller one with the substance to be heated, and place over a burner. A pair of scales, a strong six-ounce bottle, wire-netting, cord, and wax or paraffin should be provided. EXPERIMENT 10. Do SEEDS IN THEIR ORDINARY QUIESCENT STATE CONTAIN ANY WATER ? — Place a number of beans, or grains of corn or wheat in a glass bottle, making a small perforation in the cork to allow the air to escape, and heat gently. Does any moisture form on the glass ? THE SEED 11 A better test is to weigh two or three ounces of seeds, and heat them in a double boiler or in oil to prevent scorching. Weigh at intervals. If there is any loss of weight, to what is it due ? EXPERIMENT 11. Do SEEDS ABSORB WATER? — Soak a number of beans or grains of corn in water for 12 to 24 hours and compare with dry ones. What difference do you notice ? To what cause is it due ? EXPERIMENT 12. How DID WATER GET INTO THE SOAKED SEEDS? — Dry gently with a soft cloth some of the seeds used in the last experiment and press thorn lightly to see if water comes out, and where. Place a num- ber of dry seeds of different kinds — squash, bean, castor bean, quince, etc. — in warm water and notice whether any bubbles of air form on them and at what point. Examine with a lens and see if this point differs in any way from the rest of the seed cover. Does it correspond with the point from which water exuded in the soaked seeds? Could hard seeds like the squash, castor bean, buckeye, and Brazil nut get water readily without an opening somewhere in the coat ? EXPERIMENT 13. To FIND OUT WHETHER WATER is ABSORBED THROUGH THE SEED COATS. — Place in moist sand or sawdust two rows of beans as nearly as possible of the same size and weight, with the eye pressed down to the substratum in one row and turned up in the other, so that no moisture can enter through it. In the same way arrange two rows of castor beans with the little end down in one row and uppermost in the other. In the last set carefully break away the spongy mass near the tip, without injuring the parts about it. Watch and see in which rows water is absorbed most readily. What change takes place in the spongy masses at the tips of those castor beans on which they were left ? EXPERIMENT 14. Is THE RATE OF GERMINA- TION AFFECTED BY THE PRESENCE OR ABSENCE OF OPENINGS ? — Seal up with wax or paraffin all the openings of a number of air-dry peas or beans, and leave an equal number of the same size and weight untreated. Be careful that the sealing is absolutely water-tight, since otherwise the experiment will be worthless. Plant both sets and keep under like conditions of soil, temperature, and moisture. Do you see any difference in the rate of germination of the two sets? EXPERIMENT 15. Do SEEDS EXERT FORCE IN FlG< 13- ~~ Effect ABSORBING WATER ? - Fill a common six-ounce bot- s1edtl?Tabsorp- tle as full as it will hold with dry peas, beans, or tion of water. 12 PRACTICAL COURSE IN BOTANY grains of corn; then pour in water till the bottle is full. Tie a piece of wire-netting or stout sackcloth over the top to keep the seeds from being forced out. Bind both the neck and the body of the bottle tightly with strong cords encircling it in both a horizontal and vertical direction, and place under water in a moderately warm temperature. Watch for results. EXPERIMENT 16. Is THE FORCE EXERTED IN THE LAST EXPERIMENT A MERELY MECHANICAL ONE, LIKE THE BURSTING OF A WATER PIPE, OR IS IT PHYSIOLOGICAL AND THUS DEPENDENT ON THE FACT THAT THE SEEDS ARE ALIVE? — To answer this question try Exp. 15 with seeds that have been killed by heat or by soaking in formalin. Practical Questions 1. Will a pound of pop corn weigh as much after being popped as be- fore? (Exp. 10.) 2. What causes the difference, if there is any? (Exp. 10.) 3. Does the tuft of downy hairs at the tip of wheat and oat grains influence their water supply ? The spongy covering of black walnuts and almonds? The pithy inside layers of pecans and English walnuts? (Exps. 12, 13.) 4. Why will seeds, as a general thing, germinate more readily after being soaked? (Exps. 11, 14, 16.) III. TYPES OF SEEDS MATERIAL. — Dry and soaked grains of corn, wheat, or oats ; bean, squash, castor bean, and pine seed, or any equivalent specimens showing the differences as to number of cotyledons and the presence or absence of endosperm. Each student should be provided with several specimens, both soaked and dry, of the kind under consideration. Corn, beans, and wheat need to be soaked from 12 to 24 hours ; squash and pumpkin from 2 to 5 days, and very hard seeds, like the castor bean and morning-glory, from 5 to 10. If such seeds are dipped, before soaking, that is, if a small piece of the coat is chipped away from the end opposite the scar, or eye, they will soften more quickly. Keep them in a warm place with an even temperature till just before they begin to sprout, when the contents become softened. Very brittle cotyledons may be softened quickly by boiling for a few minutes. No appliances are needed beyond the pupil's individual outfit and some of the food tests given in Section I of this chapter. ii. Dissection of a grain of corn. — Examine a dry grain of corn on both faces. What differences do you notice? Sketch the grooved side, labeling the hard, yellowish outer THE SEED 13 portion, endosperm, the depression near the center, embryo, or germ. Next take a grain that has been soaked for twenty-four hours. What changes do you see ? How do you account for the swelling of the embryo? Remove the skin and observe its texture. Make an enlarged sketch of a grain on the grooved side with the coat removed, labeling the flat oval body embedded in the endosperm, cotyledon; the upper end of the little budlike body embedded in the cotyledon, plumule, the lower part, hypocotyl — words meaning, respectively, " seed leaf," " little bud/' and " the part under the cotyle- don." As this part has not yet differentiated into root and stem, we cannot call it by either of these names. The cotyledon, hypocotyl, and plumule together com- pose the embryo. Pick out the embryo and sketch as it appears under the lens. Crush it on a piece of white paper; what does it contain? Make a vertical section of another soaked grain at right angles to its broader face, and sketch, labeling the parts as they appear in profile. Make a cross section through the middle of another grain and sketch, labeling the parts as be- fore. What proportion of the grain is endosperm and what embryo ? Put a drop of iodine and of nitric acid separately on pieces of the endosperm, and note the effects. Test the seed coats and the cotyledon to see if they contain any starch. Notice that the corn grain has but one cotyledon, hence such seeds are said to be monocotyledonous, or one-cotyledoned. The grains are not typical seeds, but are selected for examina- tion because they are large and easy to handle, can be ob- tained everywhere, and germinate readily. 14 15 16 FIGS. 14-16. — Dissection of a grain of corn : 14, soaked grain, seen flatwise, cut away a little and slightly enlarged, so as to show the embryo lying in the endosperm ; 15, in profile section, dividing the grain through the embryo and cotyledon ; 16, the embryo taken out whole. The thick mass is the cotyledon ; the narrow body projecting upwards, the plumule ; the short projection at the base, the hypocotyl (after GRAY). 14 PRACTICAL COURSE IN BOTANY 17 18 FIGS. 17, 18. — A kid- ney bean : 17, side view ; 18, front view, showing h, hilum, m, micropyle. 12. Dissection of a bean. — Sketch a dry bean as it lies in the pod, showing its point of attachment and any markings that may appear on its surface. Then take it from the pod and examine the narrow edge by which it was attached. Notice the rather large scar (commonly called the eye of the bean) where it broke away from the point of attachment. This is the hilum. Near the hilum, look for a minute round pore like a pinhole. This is called the micropyle, from a Greek word meaning " a little gate," because it is the entrance to the interior of the seed coat. There was no micropyle observed in the corn grain, because it is not a true seed but a fruit inclosing a single seed.- The inclosing membrane is the fruit skin, which has become incorporated with the seed coat and taken its place as a protective covering. Compare a soaked bean with a dry one ; what difference do you perceive ? How do you account for the change in size and hardness? Find the hilum and the micropyle in the soaked bean. Lay it on one side and sketch, with the micropyle on top ; then turn toward you the narrow edge that was attached to the pod and sketch, labeling all the parts. Make a section through the long diam- eter at right angles to the flat sides, press it slightly open, and sketch it. Notice the line or slit that seems to cut the section in half longitu- dinally, and the small round object between the at one end ; can you tell what it is ? ip off the coat from a whole bean and notice its texture. Hold it up to the light and see if it shows any signs of veining. See whether the scar at the hilum extends through the kernel, or marks only the seed coat. Lay open the two flat bodies into which the kernel divides when stripped of its coats, keeping them side by side, with the part above the micropyle toward the top. Sketch their inner face and label FIG. 19. — Cotyledon of a bean, show- ing plumule. THE SEED 15 them cotyledons. Be careful not to break or displace the tiny bud packed away between the cotyledons, just above the hilum. Label the round portion of this bud, hypocotyl, and the upper, more expanded part, plumule. Which way does the base of the hypocotyl point ; toward the micropyle, or away from it ? Pick out this budlike body entire and sketch as it ap- pears under the lens. Open the plumule with a pin and exam- ine it with a lens ; of what does it appear to consist ? Do you find any endosperm around the cotyledons, as in the corn and oats? Break one of the soaked cotyledons, apply the proper tests (Exps. 2, 3, 5), and report what substances it contains. Where is the nourishment for the young plant stored ? What part of the bean gives it its value as food? Notice that in the bean the embryo consists of three parts, the hypocotyl, plumule, and the two cotyledons, which com- pletely fill the seed coats, leaving no place for endosperm. Seeds like the bean, squash, and castor bean, which have two cotyledons, are said to be dicotyledonous. 13. The castor bean. — Lay a castor bean on a sheet of paper before you with its flat side down ; what does it look like? The resemblance may be increased by soaking the seed a few minutes, in order to swell the two little pro- tuberances at the small end. Can you think of any benefit a plant might derive from this curious resemblance of its seed to an insect? Sketch the seed as it lies before you, labeling the pro- tuberance at the apex, caruncle. The caruncle is an append- age of the seed-covering developed by various plants; its uj is not always clear. What appears to be its object i castor bean? Refer to Exp. 13 and see if there is any offier purpose it might serve. Turn the seed over and sketch the other side. Notice the colored line or stripe that runs from the large end to the car- uncle. This is the rhaphe, and shows the position that would be occupied by the seed stalk if it were present. Its starting point near the large end, which is marked in fresh 16 PRACTICAL COURSE IN BOTANY seeds by a slight roughness, is the chalaza, or organic base of the seed, where the parts all come together like the parts of a flower at their insertion on the stem. Where was it situated in the common bean? How does this differ from its position in the castor bean? Where the rhaphe ends, just at the beak of the caruncle, you will find the hilum. The micropyle is covered by the caruncle, which is an outgrowth around it. Now cut a vertical section through a seed that has been soaked for several days, at right angles to the broad sides, and sketch it. Label the white, pasty mass within the seed coats, endosperm. Can you make out what the narrow white line running through the center of the endosperm, divid- ing it into two halves, represents? Make a similar sketch of a cross section. Notice the same white line running horizontally across the endosperm, di- viding it into two equal parts. To find out what these lines are, take an- other seed (always use soaked seeds for dissection) and remove the coats without injuring the kernel. Split the kernel carefully round the edges, remove half the endosperm, and sketch the other half with the delicate em- bryo lying on its inner face. You will have no difficulty now in recognizing the lines in your drawings as sections of the thin cotyledons. Where is the hypocotyl, and which way *does its base point ? Remove the embryo from the endosperm, separate the cotyledons with a pin, hold them up to the light, and observe their beautiful texture. Sketch them under the lens, showing the delicate venation. Is there any plumule? Test the endosperm with a little iodine. Does it give a -ca FIGS. 20-22. — Castor bean (slightly magnified) ; 20, back view ; 21, front view ; ch, chalaza ; r, rhaphe ; ca, caruncle ; 22, vertical section ; en, endosperm ; cc, cotyle- dons ; hy, hypocotyl ; hi, hilum ; m, micropyle. THE SEED 17 blue or a brown reaction ? Crush another bit of it on a piece of white paper and see if it leaves a grease spot. What does this show that it contains ? Test the embryo in the same way, and see whether it contains any oil. NOTE. — It should be borne in mind that the castor bean bears no rela- tion whatever to the true beans. It belongs to the spurge family, which « is botanically very remote from that of the peas and beans. — C h. - — -p 23 24 25 FIGS. 23-25. — Seed of a squash ; 23, seed from the outside ; 24, vertical section perpendicular to the broad side ; 25, section parallel to the broad side, showing inner side of a cotyledon ; a, seed coat ; c, cotyledons ; h, hypocotyl ; p, plumule. 14. Study of a squash or gourd seed. — How does the coat of a squash seed differ from that of the bean ? At the small end, look for two dots, or pinholes, close together. Refer to your drawing of the bean and see if you can make out, with the help of a lens, what they are. The bean is a curved seed, which is bent so as to bring the hilum close to the micropyle on one side. But by far the greater number of seeds are inverted, or turned over on their stalks, as you sometimes see huckleberry blossoms and bell flowers on their stems, so that when the stalk breaks away from its attachment, the scar and the micropyle come close to- gether at one end, as in the squash seed. Make a drawing of the outside of a seed, labeling all the parts you have observed ; then gently in FIG. 26. — Diagram of an inverted or anatro- pous seed, showing the parts in section : a, outer coat ; b, inner coat ; c, kernel ; d, rhaphe ; ch, chalaza ; h, hilum ; m, micropyle (After GRAY). V / 18 PRACTICAL COURSE IN BOTANY remove the hard coat, or testa, as it is called. The thin, green- ish covering that lines it on the inside is the endosperm. How does it compare in quantity with that in the corn and castor bean? How do the cotyledons compare in thickness with those of the bean? Carefully separate them and draw, label- ing the parts as you make them out. The tiny pointed object between the cotyledons at their point of union is the plumule ; is it as well developed as in the bean ? Can you see any reason why seeds like the pea and bean, which have coty- ledons too thick and clumsy to do well the work of true leaves, should have a well-developed plumule, while those with thin cotyledons, like the squash and pumpkin, do not, as a general thing, form a large plumule in the embryo ? The little pro- jection in which the cotyledons end is the hypocotyl; which way does it point ? Where did you find the micropyle to be ? Test the cotyledons and some of the endosperm for food sub- stances ; what do you find in them ? 15. Study of a pine seed. — Remove one of the scales from a pine cone and sketch the seed as it lies in place on the cone scale. Notice its point of attachment to the scale, and look near this point for a small opening, which you can easily recog- nize as the micropyle. The seed with its wing looks very much like a fruit of the maple, but differs from it in being a naked 27 28. see(j borne on the inner side of a cone scale, FIGS. 27, 28. — Pitch pine seeds: without a pod or husk or outer covering of 27, scale or open any \^A such as beans and nuts and grains carpel, with one seed . . in place ; 28, winged are provided with. Plants like the pine, ged, removed. (After Gymnosperms, a word that means " naked seeds/' in contradistinction to the Angiosperms, which bear their seeds in pods or other closed envelopes. Remove the coat from a seed that has been soaked for twenty-four hours, and examine it with a lens. Does it con- sist of one or more layers? Is there any difference in color THE SEED 19 between the inner and outer layers ? Look at the base of the hypocotyl for some loose, cobwebby appendages. These are the remains of other embryos with certain append- ages belonging to them that were formed in the endosperm, but failed to develop. Did you find remains of this kind in any of the other seeds ex- amined? Pick out the embryo from the endo- sperm and test both for food substances. Which of these do you find? Which are absent? How does the embryo differ from those already exam- ined ? How many cotyledons are there ? Make an enlarged sketch of a seed in longitudinal section, labeling correctly all the parts observed. 16. Comparison as to food value of seeds. — Make in your notebook a tabular statement after the model here given, of the food contents found in the different seeds you have ex- amined. Indicate the relative quantity of each by writing under it, in the appropriate column, the words, " much," " little," or " none/' as the case may be. By far the greater •lumber of seeds contain endosperm; that is, they consist of an embryo with more or less nourishing • * MODEL FOR RECORD OF SEEDS EXAMINED FIG. 29. - — Section of pine seed, showing the polycotyle- donous em- bryo (GRAY). SEEDS EXAMINED FOODS TESTED , Starch Sugar Oil Proteins Corn .... • Wheat .... • Bean .... Squash. . . . Castor bean . . Pine .... 20 PRACTICAL COURSE IN BOTANY matter stored about it. Even in seeds which appear to have none, the endosperm is present at some period during development, but is absorbed by the cotyledons before ger- mination. ( 17. Manner of storing nourishment. — In the various seeds examined, we have seen that the nourishment for the young plant is either stored in the embryo itself, as in the coty- ledons of the bean, acorn, squash, etc., or packed about them hi the form of endosperm, as in the corn, wheat, and castor bean. 18. The number of cotyledons. — Seeds are also classed according to the number of their cotyledons, as having onej two, or many cotyledons. The first two kinds make up the great class of Angiosperms, which includes all the true flower- ing plants and forms the most important part of the vegeta- tion of the globe. The last is characteristic of the great natural division of Gymnosperms, or naked-seeded plants, of which we have had an example in the pine. They are the most primitive type of living seed-bearing plants. Though they are not so abundant now as h^past age,s, numbering only about four hundred known species, they pie^rit many diversities of formf wSiich seefh to ally them on the one hand with the lower, or spore-bearing plants (ferns, mosses, etc.), and on the othor hand*w-ith the Angiosperms. • PracticM Questions 1. Make a list of all the seeds you can find that have very thick coty- ledons, and underline those that are used asjfood by man or beast. 2. Make a similar list tff all the kinds WTOI thin cotyledons and more or less endosperm, that are usecf for food or other purposes. 3. Do you find a greater number of foodstuffs among the one kind than the other ? 4. How do the two -kinds compare, as a general thing, in size and weight ? . 5. From whalTpart of the castor bean do we get oil ? of the peanut ? of cotton seed? (Exps. 1-6.) 6. Is there any valid objection to the wholesomeness of peanut oil, and of cottonseed lard as compared with hog's lard? (1, 3.) THE SEED 21 7. What is bran? Does it contain any nourishment? (11, 12; Exps. 1-G.) 8. What gives to Indian corn its value as food? to oats? wheat? rice? (3; Exps. 1-6.) 9. Which of these grains has the larger proportion of endosperm to embryo? (Figs. 1-3.) 10. Which contains the larger amount of nutriment in proportion to its bulk, rice or Indian corn ? 11. If you wished to produce a variety of corn rich in oil, you would select seed for planting with what part well developed? (3; Figs. 4-7.) IV. SEED DISPERSAL MATERIAL. — Fruits and seeds of any kind that show adaptations for dispersal. Some common examples are: (1) Wind: ash, elm, maple, ailanthus, milkweed, clematis, sycamore, linden, dandelion, thistle, hawkweed. (2) Water: pecan, filbert, cranberry, lotus, hickory nut, coconut — obtain one with the husk on, if possible. (3) Animal agency (involuntary) : cocklebur, tickseed, beggar-ticks, burdock ; (voluntary) almost all kinds of edible fruits, especially the bright-colored ones — wild plums, cherries, haws, dogwood, persimmons, etc. (4) Explosive and self-planting: witch-hazel, wood sorrel, violet, crane's-bill, wild vetch, peanut, medick, stork's-bill (Erodium). EXPERIMENT 17. To SHOW HOW SEEDS ARE DISPERSED BY WIND. — Take a number of winged and plumed fruits and seeds, such as those of the maple, ash, ailanthus, dandelion, clematis, milkweed, and trumpet creeper; stand on a chair or table in a place where there is a draft of air and let them all go. Which travel the farther, the winged or the plumed kinds? Which sort is better fitted to aerial transportation ? EXPERIMENT 18. DISPERSAL BY WATER. — Place in a bucket of water a hazelnut, an acorn, an orange, a cranberry, a pecan, a hickory nut, a fresh apple, and a coconut with the husk on. Which are the best floaters ? Cut open or break open the good swimmers, compare with the non-floaters, and see to what peculiarity of structure their floating qualities are due. In what situations do the cranberry and the coconut grow? Can you see any advantage to a plant so situated in producing fruits that float easily ? EXPERIMENT 19. DISPERSAL BY EXPLOSIVE CAPSULES. -- Moisten slightly some mature but unopened capsules of witch hazel, wood sorrel, rabbit pea, or violet, and leave in a warm, dry place for fifteen to forty- five minutes. What happens when the pods begin to dry ? Measure the distance to which the different kinds of seeds have been ejected. Which were thrown farthest? What was the object of the movement? What caused the explosion ? 22 PRACTICAL COURSE IN BOTANY EXPERIMENT 20. THE USE OF ADHESIVE FRUITS. — Scatter broadcast a handful of hooked or prickly seeds or fruits — cocklebur, tickseed, beggar- ticks, bur grass, etc. Are they suited for wind transportation ? Drop one of them on your sleeve, or on the coat of a fellow student ; will it stay there? What would be the effect if it became attached to the fur of a roaming animal ? Is this a successful mode of dissemination ? FIGS. 30-32. — 30, A pod of wild vetch, with mature valves twisting spirally to discharge the seed ; 31, pod of crane's-bill discharging its seed ; 32, capsules of witch- hazel exploding. 19. Agencies of dispersal. - - The means at nature's dis- posal for this purpose, as shown by the experiments just made, are four ; namely, wind, water, the explosion of capsules due to the withdrawal of water, and the agency of animals, in- cluding man. The first three are purely mechanical. The 33 34 35 36 FIGS. 33-36. — Fruits adapted to wind dispersal : 33, winged pod of pennycress ; 34, spikelet of broom sedge ; 35, akene of Canada thistle ; 36, head of rolling spin- ifex grass. last, animal agency, is either voluntary or involuntary, ac- cording as it is conscious and intentional, or accidental merely. Man, of course, is the only consciously voluntary agent. Of THE SEED 23 the four agencies named, animals and wind are the most effec- tive, and the greater number of adaptations observed will be found to have reference to these. 20. Involuntary dispersal. - - The lower animals may be voluntary agents in a way, though not designedly so, as when FIG. 37. — Good quality of clo- ver seed. FIG. 38. — Inferior quality of clover seed mixed with " screen- ings." a squirrel buries nuts for his own use and then forgets the lo- cation of his hoard and leaves them to germinate ; or when a jaybird flies off with a pecan in his bill, intending to crack and eat it, but accidentally lets it fall where it will sprout and take root. Both man and the lower animals are not only in- voluntary, but often unwilling agents of dispersal. Some of the most troublesome weeds of civili- zation have been unwittingly dis- tributed by man as he journeyed from place to place, carrying, along with the seed for planting his crops, the various weed seeds, nr "ciprpprnncrc: " Q« thp^p rmvtnrp^ enmgs, as tnese mixtures are called by dealers, with which they have been adulterated either through carelessness and ignorance, or from unavoidable causes. The neglected animals, also, that are allowed by short-sighted farmers to wander about with their hair full of cockleburs and other FlG' 39.— Dodder on red clover, showing how the seeds get mixecL 24 PRACTICAL COURSE IN BOTANY adhesive weed pests, are no doubt very unwilling carriers of those disagreeable burdens. 21. Tempting the appetite. -- This is the most important adaptation to dispersal by animals. Have you ever asked yourself how it could profit a plant to tempt birds and beasts to devour its fruit, as so many of the bright berries we find in the autumn woods seem to do? To answer this question, examine the edible fruits of your neighborhood and you will find that almost without exception the seeds are hard and bony, and either too small to be destroyed by chewing, and thus capable of passing uninjured through the digestive system of an animal ; or, if too large to be swal- lowed whole, com- pelling the animal, by their hardness or disagreeable flavor, to reject them. In cases where the seeds themselves are ed- ible and attractive, the fruits are usually armed during the growing season with % protective coverings, like the bur of the chestnut and the astringent hulls of the hick- ory nut and walnut. The acidity or other disagreeable quali- ties of most unripe fruits serves a similar purpose, while their green color, by making them inconspicuous among the foliage leaves, tends still further to insure them against molestation. 22. Voluntary agency. --The cultivated fruits and grains owe their distribution and survival almost entirely to the FIGS. 40-42. — Adhesive fruits : 40, fruit of hound's- tongue ; 41, akene of bur marigold ; 42, fruit of bur grass (cenchrus). THE SEED 25 voluntary agency of man. Dispersal by this means, whether intentional or accidental, is purely artificial, and except in the case of a few annuals like horseweed, bitterweed, ragweed, goosefoot, and other field pests that have adjusted their sea- son of growth and flowering to the conditions of cultivation, is not correlated with any special modification of the plants for self-propagation. On the contrary, many of the most widely distributed weeds of cultivation, such as the ox-eye daisy, the rib grass, mayweed and bitterweed, possess very imperfect natural means of dispersal, and are largely depend- ent for their propagation on the involuntary agency of man. 23. Use of the fruit in dispersal. — It will be seen from the foregoing observations that the fruit plays a very important part in the work of dispersal, most of the adapta- tions for this pur- pose being con- nected with it. In cases where a number of seeds are contained in a large pod that could not conveniently be blown about by the breeze, adaptations for wind dispersal are attached to the individual seeds, as in the willow, milkweed, trumpet creeper, and paulonia; but as a general thing, adaptations of the seed are for protection, the work of dispersal being provided for by the fruit. In the case of the large class of plants known as " tumbleweeds, " the whole plant body is fitted to assist in the work of transporta- tion. Such plants generally grow in light soils and either have very light root systems, or are easily broken from their FIG. 43. — A fruiting plant of winged pigweed (Cycloloma), showing the bunchy top and FIG. 44. — Panicle of weak anchorage of a typical "old witch grass," a com- tumbleweed. mon tumbleweed. 26 PRACTICAL COURSE IN BOTANY anchorage and left to drift about on the ground. The spread- ing, bushy tops become very light after fruiting, so as to be easily blown about by the wind, dropping their seeds as they go, until they finally get stranded in ditches and fence corners, where they often accumulate in great numbers during the autumn and winter. 24. The advantages of dispersal. — Seed cannot germinate unless they are placed in a suitable location as to soil, moisture, and temperature. In order to increase the chances of secur- ing these conditions, it is clearly to the advantage of a species that its seeds should be dispersed as widely as possible, both that the seedlings may have plenty of room, and that they may not have to draw their nourishment from soil already exhausted by their parents. The farmer recognizes this principle in the rotation of crops, because he knows that successive growths of the same plant will soon exhaust the soil of the substances re- quired for its nutrition, while they may leave it richer in nourishment for a different crop. 25. Self-planting seeds. - Dispersal is not the only problem the seed has to meet. The majority of seeds cannot germinate well on top of the ground, and must depend on various agencies for getting under the soil. Some of them do this for themselves. The seeds of the stork's-bill, popularly known as "filarees," have a sharp-pointed base and an auger-shaped appendage at the apex, ending in a projecting arm (the " clock" of the filaree) by which it is blown about by the wind with a whirling motion FIG. 45. — Self -planting pod of peanut. THE SEED 27 till it strikes a soft spot, when it begins at once to bore its way into the ground. The common peanut is another exam- ple. The blossoms are borne under the leaves, near the base of the stem, and as soon as the seeds begin to form, the flower stalks lengthen several inches, carrying the young pods down to the ground, where they bore into the soil and ripen their seeds. Practical Questions 1. Name the ten most troublesome weeds of your neighborhood. 2. What natural means of dispersal have they ? 3. Which of them owe their propagation to man ? 4. Are there any tumbleweeds in your neighborhood ? 5. Would you expect to find such weeds in a hilly or a well- wooded region? (19; P]xp. 17.) 6. What situations are best fitted for their propagation? (19, 23; Exp. 17.) 7. Make a list of all the fruits and seeds you can think of that are adapted to dispersal by wind ; by water ; by animals. 8. By what means of dissemination, or protection, or both, is each of the following distinguished : the squash; apple; fig; pecan; poppy; bean ; beggar-tick ; linden ; grape ; rice ; pepper ; olive ; cranberry ; jimsonweed; thistle; corn; wheat; oats? 9. What is the agent of dispersion, or what the danger to be provided against, in each case ? 10. Could our cultivated fruits and grains survive in their present state without the agency of man ? (22. ) 11. Name all the plants you can think of that bear winged seeds and fruits ; are they, as a general thing, tall trees and shrubs, or low herbs ? 12. Name all you can think of that bear adhesive seeds and fruits ; are they tall trees or low herbs ? 13. Give a reason for the difference. (Exps. 17, 20.) 14. Why is the dandelion one of the most widely distributed weeds in the world? (19; Exp. 17.) 15. Is the wool that covers cotton seed for dispersal or protection ? 16. What advantage to the Indian shot (canna) is the excessive hardness of its seeds? (21.) 17. What is the use to the species, of the bitter taste of lemon and orange seed? (21.) 18. Why are the seeds of dates and persimmons and haws so hard? (21.) 28 PRACTICAL COURSE IN BOTANY 19. Do you find any edible seeds without protection? If so, account for the want of it. (21, 22.) 20. Name some of the agencies that may assist in covering seeds with earth. 21. Do you know of any seeds that bury themselves? 22. The seeds of weeds and other refuse found mixed with grain sold on the market are known, commercially, as " screenings." Wheat brought to mills in Detroit showed screenings that contained, among other things, seeds of black bindweed, green foxtail grass, yellow foxtail, chess, oats, ragweed, wild mustard, corn cockle, and pigweed. Can you mention some of the ways in which these foreign substances may have gotten into the crop and suggest means for keeping them out ? Field Work The subjects treated in the foregoing chapter are, in general, better suited to laboratory than to field work. There are some details, however, which can be observed to advantage out of doors. Many of the seeds found in your walks will show peculiarities of shape and external markings and color that will invite observation. Examine also the contents of dif- ferent kinds you may meet with, as to the presence or absence of endosperm and the arrangement and development of the embryo. Note: (1) whether, as a general thing, there is any difference in size and weight and amount of nourishing matter in the two kinds ; (2) the greater variety in the shape and arrangement of the cotyledons in the albuminous kind, and in the ar- rangement of the embryo ; (3) the differences in the development of the plumule in the two kinds, — and give a reason for the facts observed. Among the different seeds you may find, look for adaptations for dispersal, and decide to what particular method each is suited. Study the agencies by which various kinds may get covered with soil. If the common stork' s- bill (Erodium cicutarium) grows in your neighborhood, its seeds will well repay a little study, and if there is a field of peanuts within reach, do not fail to pay it a visit. CHAPTER II. GERMINATION AND GROWTH I. PROCESSES ACCOMPANYING GERMINATION MATERIAL. — A pint or two of corn, peas, beans, or any quickly germi- nating seed. APPLIANCES. — Matches ; wood splinters ; gas jet or alcohol lamp ; test tubes ; a small quantity of mercuric oxide ; a thermometer ; a couple of two-quart preserve jars, and a smaller wide-mouthed bottle that can be put into one of them ; some limewater ; a glass tube (the straws used by druggists for soft drinks will answer). 26. Preliminary exercises. — Before taking up the study of germinating seeds, it is important to learn from what sources the organic substances used by the growing plant are derived, and some of the processes that accompany growth and development. EXPERIMENT 21. To SHOW THE CHANGES THAT ACCOMPANY OXIDA- TION. — Strike a match and let it burn out. Examine the burnt portion remaining in your hand ; what changes do you notice ? These changes have been caused by the union of some substance in the match with something outside of it, in the act of burning ; let us see if we can find out what this outside substance is. EXPERIMENT 22. To SHOW THE ACTIVE AGENT IN OXIDATION. - Heat some mercuric oxide in a test tube over the flame of a burner. The heat will cause the oxygen to separate from the mercury, and in a short time the tube will be filled with the gas. Extinguish the flame from a lighted splinter and thrust the glowing end into the tube ; what happens ? The oxygen unites with something in the wood and causes it to burn just as the match did. Compare your burnt splinter with the burnt end of the match ; what resemblance do you notice between them ? EXPERIMENT 23. To SHOW THAT CARBON DIOXIDE is A PRODUCT OF OXIDATION. — Your experiment with the match showed that ignition is accompanied by heat, and if active enough, by light, and also that it left behind a solid substance in the form of charcoal. But how about the part that united with the oxygen to produce these results? 29 30 PRACTICAL COURSE IN BOTANY Let us see what became of it. Hold a lighted candle under the open end of a test tube, or under the mouth of a small glass jar. Does any vapor collect on the inside? After two or three minutes quickly invert the jar or the tube, and thrust in a lighted match: what happens? Can the substance now in the jar be ordinary air? Why not? (Exps. 21, 22.) Pour in a small quantity of limewater, holding your hand over the mouth of the tube to prevent the air from getting in ; the gas inside, being heavier than air, will not escape immediately unless agitated. What change do you notice in the limewater ? It has been proved by experiment that the kind of gas formed by the burning candle has the property of turning limewater milky; hence, whenever you see this effect produced in limewater, you may conclude that this gas, known as carbon dioxide, is present ; and conversely, the presence of carbon dioxide, especially if accompanied by some of the other effects observed, as the giving out of heat and moisture, may be taken as evidence that some process similar to that going on in the burning candle is, or has been, at work. EXPERIMENT 24. Do THESE EFFECTS ACCOMPANY ANY OF THE LIFE PROCESSES OF ANIMALS ? — Blow your breath against the palm of your hand ; what sensation do you feel ? Blow it against a mirror, or a piece of common glass ; what do you see ? Blow through a tube into the bottom of a glass containing limewater ; how is the water affected ? How do these facts cor- * respond with the results of Exp. 23 ? EXPERIMENT 25. Is THERE ANY EVIDENCE THAT A SIMILAR PROCESS GOES ON IN PLANTS ? — (1) Half fill a small, wide-mouthed jar with limewater, place it in- side a larger one (Fig. 46), and fill the space between them, up to the neck of the smaller vessel, with well- soaked peas, beans, or barleycorns, on a bed of moist cotton or blotting paper. Cover with a piece of glass and keep at a moderately warm temperature. (2) As a control experiment, place beside this another jar ar- ranged in precisely the same way, except that seeds must be used whose vitality has been destroyed by heat. To prevent the entrance of germs among the dead seeds, which might cause fermentation and thus interfere with the experiment, set the jar containing them in a vessel of water and boil an hour or two before the experiment begins. Otherwise, treat precisely as in (1). After germination has taken place in (1), what change do you notice in the limewater ? If the effect is not apparent, gently stir with a straw or FIG. 46. — Dia- grammatic section, showing arrange- ment of jars for Exp. 25. GERMINATION AND GROWTH 31 a glass rod to mix it with the gas in the larger jar. Has the limewater in the control experiment undergone the same change? (It may show a slight milkiness due to the carbon dioxide in the air.) Insert a thermom- eter among the seeds in both of the larger jars, and compare their tem- perature with that of the outside air; which shows the greater rise? From this experiment and the last one, what process, common to animals, would you conclude has been going on in the germinating seeds ? NOTE. — Heat in germinating seeds is not always due to this cause alone, but is sometimes increased by the presence of minute organisms called bacteria. Germinating barley and rye in breweries sometimes show an increase in temperature of 40 to 70 degrees, due to these organisms, and spontaneous combustion in seed cotton has been reported from the same cause. 27. Oxidation. - - The process that brought about the results observed in the foregoing experiments, and popularly known as combustion, is more accurately defined by chemists as oxidation. It takes place whenever substances enter into new combinations with oxygen. The most familiar examples of it are when oxygen enters into combination with substances containing carbon. It was the union of a portion of the oxygen of the air in Exp. 21, and of that in the tube in Exp. 22, with some of the carbon in the wood, that caused the burning. The effect was more marked in the second case because the oxygen in the tube was pure, while in the air it is mixed with other substances. 28. Carbon. - - The black substance left in your hand after oxidation of the wood in Exps. 21 and 22 is carbon. It composes the greater part of most plant bodies, and, in fact, is the most important element in the realm of organic nature. There is not a living thing known, from the smallest microscopic germ to the most gigantic tree in existence, that does not contain carbon as one of its essential constituents. 29. Carbon dioxide. - - The gas produced by the burning candle in Exp. 23, by the germinating seeds in Exp. 25, and expelled from your own lungs in Exp. 24, is carbon dioxide. Chemists designate it by the symbol CO2, which means that it consists of one part carbon to two parts oxygen. It is an 32 PRACTICAL COURSE IN BOTANY invariable product wherever the oxidation of substances containing carbon goes on. Heat and moisture are evolved at the same time, and if oxidation is very active, as in Exps. 21 and 22, light also. When the process takes place very slowly, no light is evolved, and so little heat as to be imper- ceptible without special observation. Hence, oxidation may go on around us and even in our own bodies without our being conscious of the fact. Carbon dioxide is of prime importance to the well-being of plants. It furnishes the material from which the greater part of their organic food is derived, as will be seen when we take up the study of the leaf and its work. To animals, on the contrary, its presence is so injurious that if the pro- portion of it in the air we breathe ever rises much above 1 part to 1000, the ill effects become painfully sensible. It is not, however, as was formerly supposed, a poison, the harm it does being to decrease the proportion of oxygen in the atmosphere so that animals cannot get enough of it to breathe, and die of suffocation. 30. Respiration in plants and in animals. — It was shown in Exp. 24 that respiration in animals is accompanied by the products of oxidation ; hence we conclude that respiration is a form of oxidation. And since these same products are given off by plants (Exp. 25), the inference is clear that the same process goes on in them. But in plants the life func- tions are so much more sluggish than in animals that it is only in their most active state, during germination and flowering, that evidence of it is to be looked for. 31. Respiration and energy. — In plants, as in animals, respiration is the expression or measure of energy. Sleeping animals breathe more slowly than waking ones, snakes and tortoises more slowly than hares and hawks. The more we exert ourselves and the more vital force we expend, the harder we breathe ; hence, respiration is more active in children than in older persons and in working people than in those at rest. It is the same with plants ; respiration is most GERMINATION AND GROWTH 33 perceptible in germinating seeds and young leaves, in buds and flowers, where active work is going on. Hence, in this condition they consume proportionately larger quantities of oxygen and liberate correspondingly larger quantities of carbon dioxide, with a proportionate increase of heat. In some of the arums, — calla lily, Jack-in- the-pulpit, colo- casia, etc., — and in large heads of compositse, like the sun- flower, where a great number of small flowers are brought together within the same protecting envelope, the rise of temperature is sometimes so marked that it may be per- ceived by placing a flower cluster against the cheek. Practical Questions 1. What is charcoal? (28.) 2. Is any of this substance contained in the seed? in the flour and meal made from seed ? (28; Exp. 25.) 3. What combination takes place when the cook lets the stove get too hot and burns the biscuits ? (27, 28.) 4. Of what does the burned part consist? (28.) What was it before it was burned? (27, 28). 5. Which burns the more readily, an oily seed or a starchy one? Which leaves the more solid matter behind ? (Suggestion : test by put- ting a bean, or a large grain of corn, and an equal quantity of the kernel of a Brazil nut on the end of apiece of wire and thrusting into a flame.) 6. Is there any rational ground for the statement that the wooden buildings formerly used on Southern plantations as cotton ginneries were sometimes destroyed through spontaneous combustion due to the heat generated by piles of decaying cotton seed ? (Exp. 25, Note.) n. CONDITIONS OF GERMINATION MATERIAL. — Several ounces each of various kinds of seed. For the softer kinds, pea, bean, corn, oats, wheat are recommended; for those with harder coverings, squash, castor bean, apple, pear, or, w ere ob- tainable, cotton ; for still harder kinds, persimmon and date seeds, or the stones of plum and cherry. APPLIANCES. — 1 dozen common earthenware plates for germinators ; 1 dozen two-ounce wide-mouthed bottles; 2 common glass tumblers; clean sand, sawdust, or cotton batting, for bedding ; a double boiler ; a gas burner, or a lamp stove. 34 PRACTICAL COURSE IN BOTANY 32. Recording observations. — For this purpose a page should be ruled off in the notebook of each student, after the model here given, and the facts brought out by the differ- ent experiments set down as observed. NUMBER OF SEEDS GERMINATED No. of hours . . No. of vessel. . No. of vessel. . No. of vessel . . No. of vessel. . No. of vessel . . No. of vessel. . 1 24 48 72 4d. 5 d. 6d. 7d. 8d. 10 d. 2w. 2 3 4 ~ 5 6 EXPERIMENT 26. CAN SEEDS HAVE TOO MUCH MOISTURE ? — Drop a number of dry beans or grains of corn, oats, or other convenient seed, into a vessel with a bedding of cotton or paper that is barely moistened, and an equal number of soaked seeds of the same kind into another vessel with a saturated bedding of the same material. In a third vessel place the same number of soaked seed, covering them partially with water, and in a fourth cover the same number entirely. Label them 1, 2, 3, and 4; keep all together in a warm, even temperature, and observe at intervals of twenty-four hours for a week. What condition as to moisture do you find most favorable to germination ? Would seeds germinate in the entire absence of moisture ?. How do you know ? EXPERIMENT 27. WAS IT THE PRESENCE OF TOO MUCH WATER, OR THE LACK OF AIR CAUSED BY IT, THAT INTERFERED WITH GERMINATION IN THE LAST EXPERIMENT? — To answer this question experimentally is not easy, since it is difficult to obtain a complete vacuum without special appliances. The simplest way is to fill with mercury a glass tube 30 inches long, closed at one end, and invert it over a small vessel — a tea- cup, or an egg cup will answer — containing mercury enough to cover the bottom to a depth of two or three centimeters (see Appendix, Weights and Measures, for English equivalents.) The tube must be supported in such a way that its lower end will dip into the mercury without touching the bottom of the vessel. With a pair of forceps insert under the mouth of the tube two or three seeds that have been well soaked in water deprived of air by previous boiling. Being lighter than mercury, they will float to the top, where there is a complete absence of air while other conditions GERMINATION AND GROWTH 35 favorable to germination are present. Before releasing, they should be well shaken under the mercury to free them from air bubbles, and if the coats are loose fitting so that they can be removed without injury to the parts inclosed in them, they should be slipped off in order to get rid of any imprisoned air they may contain. Additional moisture may be supplied, if necessary, by injecting, by means of a medicine dropper inserted under the mouth of the tube, a drop or two of water that has been previously boiled. Keep in a warm, even temperature, under conditions favorable to germination, and compare the behavior of the seeds with those placed in the different vessels in Exp. 26. If appliances for this experiment are lacking, a rough approximation can be made by using the seeds of aquatic plants, such as the lotus, water lily, and the so-called Chinese sacred bean, sold in the variety stores, which we know are capable of germinating in the limited amount of air contained in ordinary soil water. Place an equal number of such seeds, of about the same size and weight, on a bedding of common garden soil in two glass tumblers. Fill one vessel a little over half full of ordinary soil water and the other to the same height with water from which the air has been expelled by boil- ing. Pour over the liquid a film of sweet oil or castor oil, to prevent the access of air, leaving the surface of the water in the other vessel exposed. In which do the seeds come up most freely ? Some seeds, especially those rich in proteins, as peas and beans, ill germinate in a vacuum, because oxygen is supplied for a time by the chemical decom- position of substances in their tissues which contain it, but when these are exhausted, respiration ceases and death ensues. EXPERIMENT 28. DOES THE DEPTH AT WHICH SEEDS ARE PLANTED AFFECT THEIR GERMINATION ? — Plant a number of peas or grains of corn at different depths in a wide-mouthed glass jar filled with moist sand, as shown in Fig. 47, the lowest ones at the bottom, the top ones barely covered. Try different kinds of seed and grain, — radish, squash, cotton, or wheat, — and watch them make their way to the surface. Do you notice any difference in this respect between large seed and small ones ? Between those with thick coty- ledons and thin ones ? At what depth do you find, from your recorded observations, that seed germinate best? FIG. 47. — To find out the proper depth at which to plant 36 PRACTICAL COURSE IN BOTANY EXPERIMENT 29. WHAT TEMPERATURE is MOST FAVORABLE TO GERMI- NATION ? — Put half a dozen soaked beans on moist cotton or sawdust in three wide-mouthed bottles of the same size or in germinators arranged as in Figs. 48, 49, the seed also being selected with a view to similarity of size and weight. Keep one at a freezing temperature ; the second in a temperature of 15° to 20° C. (see Appendix for Fahrenheit equivalents) ; and the third, at 30° C. If a place can be found near a stove or a register, where an even temperature of about 125° F. is maintained, place a fourth receptacle there. Observe at intervals of twenty- four hours for a week or ten days, keeping the temperature as even as possible, and maintaining an equal quantity of moisture in each vessel. Make a daily record of your observations. What temperature do you find most favorable to germination ? FIGS. 48,49. — Home-made ger- minators : 48, closed ; 49, showing interior arrangement. EXPERIMENT 30. AT WHAT TEMPERATURE DO SEEDS LOSE THEIR VITAL- ITY ? — Place about two dozen each of grains of corn, beans, squash seed, and castor beans, with an equal number of plum or cherry stones, in water, and heat to a temperature of 150° F. After an exposure of ten minutes, take out six of each kind and place in germinators made of two plates with moist sand or damp cloth between them, as shown in Figs. 48, 49. Raise the temperature to 175° F., and after ten minutes take out six more of each kind of seed and place in another germinator. Raise the water in the vessel to 200°, take out another batch of seeds; raise to the boiling point for ten minutes more, and plant the remain- ing six of each lot. Number the four germinators, and .observe at in- tervals of twenty-four hours for two weeks. The harder kinds should be kept under observation for three or four weeks, as they germinate slowly. Try the same experiments with the same kinds of seeds at a dry heat, using a double boiler to prevent scorching, and record observations as before. EXPERIMENT 31. TIME REQUIRED FOR GERMINATION. — Arrange in germinators seeds of various kinds, such as corn, wheat, peas, turnip, apple, orange, grape, castor bean, etc. "Clip" some of the harder ones and keep all the kinds experimented with under similar conditions as to moisture, temperature, etc., and record the time required for each to sprout. What is the effect of clipping, and why ? EXPERIMENT 32. ARE VERY YOUNG OR IMMATURE SEEDS CAPABLE OF GERMINATING ? — Plant some seeds from half-grown tomatoes, and grains GERMINATION AND GROWTH 37 of wheat, oats, or barley before they are ready for harvesting. Try as many kinds as you like, and see 'how many will come up. Notice whether there is any difference in the health and vigor of plants raised from seeds in different stages of maturity. EXPERIMENT 33. THE RELATIVE VALUE OF PERFECT AND INFERIOR SEED. — From a number of seeds of the same species select half a dozen of the largest, heaviest, and most perfect, and an equal number of small, inferior ones. If a pair of scales is at hand, the different sets should be weighed and a record kept for com- parison with the seed- lings at the end of the experiment. Plant the two sets in pots con- taining exactly the same kind of soil, and keep under identical conditions as to light, temperature, and moisture. Keep the seedlings under obser- vation for two or three weeks, making daily notes and occasional drawings of the height and size of the stems, and the number of leaves produced by each. 33. Resistance to heat and cold.— In making experi- 50 51 FIGS. 50, 51. — Stem development of seedlings: 50, raised from healthy grains of barley ; weight, 39.5 grams (about 500 grs.) ; 51, raised under exactly similar conditions from the same number of inferior grains ; weight, 23 grams (about 350 grs.). 52 53 FIGS. 52, 53. — Improvement of corn by selection: 52, original type ; 53, improved type developed from it. ments with regard to temperature, notice how the extremes tolerated are influenced, first, by the length of time the seeds are exposed ; second, by the amount of water contained in them ; and third, by the nature of the seed coats. Every farmer knows that the effect of freezing is much more in- 38 PRACTICAL COURSE IN BOTANY jurious to plants or parts of plants when full of sap (water) than when dry. This, in the opinion of the most recent investigators, is because the water in the spaces outside the cells freezes first and as moisture is gradually withdrawn from the inside to take its place, the soluble salts which may be present in the cell sap become more concentrated, and by their chemical action on the contained proteins cause them to be precipitated, or " salted out," as we see sugar or salt precipitated from solutions of those substances when water is withdrawn by evaporation. In this way, it is believed, the fundamental protoplasm of the cell may be so disorganized that death ensues if the freezing is continued long enough, since the protein precipitates become " denatured " and cannot be reabsorbed if kept in a solid state too long. The length of time necessary to produce death from this cause is, of course, different in different plants, according to the kind of salts dissolved in the sap and the nature of the proteins acted on by them. The proteins in the sap of Begonia, or Pelargo- nium, plants which are very sensitive to cold, yield a dena- tured precipitate at, or a little below the freezing point of water, while those of winter rye withstand a temperature of -15° C., and of pine needles, -40° C. Mechanical injury through rupture of parts by freezing is not apt to cause serious damage except in cases of sudden and violent cold at a time when the tissues are gorged with sap, as not infrequently happens during the abrupt changes of temperature which sometimes occur in spring after the trees have put forth their leaves. In an extreme case of this kind, the writer has seen the trunk of an oak a foot or more in diameter split in deep seams from the effects of freezing. 34. The length of time during which seeds may retain their vitality. — No direct experiment can be made to test this point, since it would require months, or even years, covering in some instances more than the lifetime of a genera- tion. It has been stated on good authority that seeds of the GERMINATION AND GROWTH 39 water chinquapin (Nelumbo) have germinated after more than a hundred years, and moss sp'bres preserved in her- bariums, after fifty. But the records in such cases are not always trustworthy, and there is absolutely no foundation for the statements sometimes made about the germination of wheat grains found preserved with mummies over two thousand years old. If kept perfectly dry, however, seed may sometimes be preserved for months, or even years. Peas have been known to sprout after ten years, red clover after twelve, and tobacco after twenty. Ordinarily, however, the vitality of seeds diminishes with age, and in making ex- periments it is best to select fresh ones. Those used for comparison should also, as far as possible, be of the same size and weight. 35. Effect of precocious germination. — It has been found by experiment that plants raised from immature seed, when they will germinate at all (Exp. 32), yield earlier and larger crops than the same kinds from mature seed. Early toma- toes and some other vegetables are produced in this way. The majority of seeds, however, require a period of rest before beginning their life work. Those that are forced to take up the burden of " child labor " show the effect of such abnormal condition by yielding fruits that are smaller and less firm than those raised from mature seed, so that they do not keep well and have to be marketed quickly. Under what circumstances does it pay to cultivate such fruits? Practical Questions 1. What are the principal external conditions that affect germination? (Exps. 26-29.) 2. What effect has cold? want of air? too much water? 3. Is light necessary to germination ? 4. What is the use of clipping seeds ? (Exps. 12, 13, 14, and Material, p. 12.) 5. In what cases should it be resorted to ? (Exp. 31.) 6. Why will seed not germinate in hard, sun-baked land without 40 ' PRACTICAL COURSE IN BOTANY abundant tillage ? Why not on undrained or badly drained land ? (Exps. 26, 27.) 7. Will seeds that have lost their vitality swell when soaked? (Exp. 16. ) 8. Are there any grounds for the statement that the seeds of plums boiled into jam have sometimes been known to germinate ? 1 (33; Exp. 30.) 9. Could such a thing happen in the case of apple -or sunflower seed, and why or why not ? (33.) 10. Does it make any difference in the health and vigor of a plant whether it is grown from a large and well-developed seed or from a weak and puny one? (Exp. 33.) 11. Would a farmer be wise who should market all his best grain and keep only the inferior for seed ? 12. What would be the result of repeated plantings from the worst seed? 13. Of constantly replanting the best and most vigorous ? 14. Suppose seed would germinate without moisture; would this be an advantage, or a disadvantage to agriculturists ? 15. Why is a cool, dry place best for keeping seeds ? (Exps. 26, 29.) 16. Why are the earliest tomatoes found in the market usually smaller than those offered later ? (35.) 17. Why is continued rain so injurious to wheat, oats, and other grains before they are mature enough to be harvested ? (35; Exp. 32.) 18. Would the same effect be likely to occur in the case of very oily seeds, such as flax and castor beans ? Why ? (Suggestion : try the effect of putting water on a piece of oiled paper.) 19. Explain why many seeds cannot germinate successfully without air. (30,31; Exp. 25.) 20. Mention some of the practical advantages that a farmer, a gardener, or a careful housewife might gain from experiments like those made in this section. 21. Explain why seeds can endure so much greater extremes of tempera- ture than growing plants. (23, 33.) III. DEVELOPMENT OF THE SEEDLING MATERIAL. — Seedlings of various kinds in different stages of growth. It is recommended that the same species be used that were studied in Section III, Chapter I, or such equivalents as may have been substituted for them. Enough should be provided to give each pupil three or four specimens in different stages of development. Seeds, even of the same kind, 1 Vines, " Lectures on the Physiology of Plants," p. 282. See also Sachs, "Physiology of Plants." GERMINATION AND GROWTH 41 develop at such different rates that it will probably not be necessary to make more than two plantings of each sort, from 2 to 5 days apart. Soaked seeds of corn and wheat will germinate in from 3 to 7 days, according to the temperature; oats in 1 to 4; beans in 4 to 6; squash and castor beans in from 8 to 10. Very obdurate ones may be hastened by clipping. Keep the germinators in an even temperature, at about 70° to 80° F. Pine is .a very difficult seed to germinate, requiring usually from 18 to 21 days. By soaking the mast for twenty-four hours and planting in damp sand or sawdust kept at an even temperature of 23° C. or about 75° F., specimens may be obtained. 36. Seedlings of monocotyls. — Examine a seedling of corn that has just begun to sprout ; from which side does the seedling spring, the plain or the grooved one ? Refer to your sketch of the dry grain and see if this agrees with the position of the embryo as observed in the seed. Make sketches of four or five seedlings in different stages of advancement, until you reach one with a well-developed blade. From what part of the embryo has each part of the seedling developed? Which part -first appeared above ground?.' I§ it straight, or bent in any way? In what direction does the plumule grow ? The hypocotyl ? Does the cotyledon appear above ground at all? Slip off the husk and see if there is any differ- ence in the size and appearance of the contents as you proceed from the younger to the older plants. How would you ac- count for the difference? 37. The root. — Examine the lower end of the hypocotyl and find where the roots originate ; would you say that they are an outgrowth from the stem, or the stem from the root? Observe that the root of the corn does not continue to grow in a single main axis like that of the castor bean, but that numerous adventitious and secondary roots spring from FIGS. 54, 55.— Seed- ling of corn (after GRAY) : 54, early stage of germination ; 65, later stage. 42 PRACTICAL COURSE IN BOTANY various points near the base of the hypocotyl and spread out in every direction, thus giving rise to the fibrous roots of grains and grasses. 38. Root hairs. — Notice the grains of sand or sawdust that cling to the rootlets of plants grown in a bedding of that kind. Examine with a lens and see if you can account for their presence. Lay the root in water on a bit of glass, hold up to the light and look for root hairs ; on what part are they most abundant? The hairs are the chief agents in absorbing moisture from the soil. They do not last very long, but are constantly dying and being renewed in the younger and tenderer parts of FIG. 56. — Seed- the root. These are usually broken away in ling of wheat, with tearing the roots from the soil, so that it is not easy to detect the hairs except in seedlings, even with a microscope. In oat, maple, and radish seedlings they are very abundant and clearly visible to the naked eye. The amount of absorbing surface on a root is greatly increased by their presence. 39. The root cap. — Look at the tip of the root through your lens and notice the soft, transparent crescent or horseshoe- shaped mass in which it terminates. This is the root cap and serves to protect the tender parts behind it as the roots burrow their way through the soil. Being soft and yielding, it is not so likely to be in- jured by the hard substances with which it comes in contact as would be the more compact tissue of the roots. It is composed of loose cells out of which the solid root substance is being formed; the growing point of the root, g, is at the extremity of the tip just behind the cap, c (Fig. 57). The cap is very apparent in a seedling of corn, and can easily c FIG. 57. — Diagram- matic section of a root tip : a, cortex ; b, central cylinder in which the conducting vessels are situated ; c, root cap ; g, growing point. GERMINATION AND GROWTH 43 be seen with the naked eye, especially if a thin longitudinal section is made. It is also well seen in the water roots of the common duckweed (Lemna), and on those developed by a cutting of the wandering Jew, when placed in water. Are there any hairs on the root cap ? Can you account for their absence ? NOTE. — For a minute study of the structure of roots, see 67. 40. Organs of vegetation. - - The three parts, root, stem, and leaf, are called organs of vegetation in contradistinction to the flower and fruit, which constitute the organs of reproduction. The for- mer serve to maintain the plant's indi- vidual existence, the latter to produce seed for the propagation of the species, so we find that the seed is both the be- ginning and the end of vegetable life. 41. D efinitions . — Organ is a general name for any part of a living thing, whether animal or vegetable, set apart Flo 58._seediings of bean to do a certain work, as the heart for in different stages of growth : , , , cc, cotyledons, showing the pumping blood, or the stem and leaves piumuie and hypocotyi before of a plant for conveying and digesting germination ; a, b d, and e, ° ° successive stages of advance- Sap. By function IS meant the ment. At d the arch of the particular work or office that an organ %$£ ; at .tt£±S«£ has to perform. erected itself . 42. Seedlings of dicotyls. The bean. — Sketch, with- out removing it, a bean seedling that has just begun to show itself above ground ; what part is it that protrudes first ? Sketch in succession four or five others in different stages of advancement. Notice how the hypocotyi is arched where it breaks through the soil. Does this occur in the monocotyls examined? Do the cotyledons of the bean appear above ground? How do they get out? Can you perceive any advantage in their being dragged out of the ground back- wards in this way rather than pushed up tip foremost? 44 PRACTICAL COURSE IN BOTANY What changes have the cotyledons undergone in the suc- cessive seedlings? Remove from the earth a seedling just beginning to sprout and sketch it. From what point does the hypocotyl protrude through the coats ? Does this agree with its position as sketched in your study of the seed? In which part of the embryo does the first growth take place ? Remove in succession the several seedlings you, have sketched and note their changes. How does the root differ from that of the corn and oats ? The first root formed by the extension of the hypocotyl is the primary root and should be so labeled in your drawings ; the branches that spring from it are secondary roots. Look for root hairs ; if there are any, where do they occur? 43. Germination of the squash. — How does the manner of breaking through the soil compare with that of the bean ? FIG. 59. — Stages in the germination of a typical seedling of the squash family : a, a seed before germination ; 6, c, e, the same in different stages of growth ; d, the empty testa, with kernel removed ; hi, hilum ; m, micropyle ; p, p, the peg in the heel ; h, h, h, the hypocotyl ; ar, arch of the hypocotyl ; co, cotyledons ; pi, plumule ; pr, primary root ; sc, secondary roots. With the corn? From which end of the seed, the large or the small one, does the hypocotyl spring ? Do the cotyledons come above ground ? How do they get out of the seed coat ? Notice the thick protuberance developed by the hypocotyl and pressing against the lower half of the coat at the point where the hypocotyl breaks through. This is called the GERMINATION AND GROWTH 45 " peg " ; can you tell its use? Could the cotyledons get out of their hard covering without it? Slip the peg below the coat in one of your growing specimens, leave it in the soil, and see what will happen. How do the cotyledons of the squash differ from those of the bean as they come out of the seed cover? Do they act as foliage leaves? Do you see any difference in the development of the plumule in the two seeds (Figs. 19, 25) to account for the different behavior of the cotyledons? Sketch three seedlings in different stages, labeling correctly the parts observed. Make a similar study of the castor bean, or other seedling selected by your teacher, and illustrate by drawings. 44. Arched and straight hypocotyls. - - This difference in the manner of getting above ground is an important one. That by means of the arched hypocotyl isk in general, charac- teristic of the process of germination in which the cotyledons come above ground, while the straight kind, which was illus- trated in the corn and wheat, is the prevail- ing method when the cotyledons remain below ground. Can you give a reason for the difference? 45. Polycotyledons ; germination of the pine. — Examine a pine seedling just begin- ning to sprout. What part emerges first from the seed coat? Where does it break through ? Where did you find the micropyle in the pine seed? (15.) Can you give a reason why the hypocotyl in seeds should break through the coats at this point ? How FIG. co! — Pine do the cotyledons get out of the testa? Is seedling (After GBAY)' the hypocotyl arched or straight in germination ? How does it compare with the bean and squash in this respect ? With the corn ? Is any endosperm left in the testa after the cotyle- dons have come out? What has become of it? Do the cotyledons function as leaves ? How many of them has the specimen you are studying ? Notice the little knob or button 46 PRACTICAL COURSE IN BOTANY at the upper end of the hypocotyl, just above the point where the cotyledons are attached ; this is the epicotyl, or part above the cotyledons, here identical with the plumule ; does it develop as rapidly as in the other seedlings you have ex- amined ? 46. Relation of parts in the seedling. — Before leaving this subject, it is important to fix clearly in mind the different parts of the germinating seedling and their relation to both the embryo from which they originated and the plant into which they are to develop. The part labeled " hypocotyl " in your sketches is all that portion of the embryo below the point of attachment of the cotyledons. In germination its upper part will become the stem, and in the embryo con- stitutes the caulicle, or stemlet, while its lower part, from which the root will develop, is the radicle, or rootlet ; hence the term " hypocotyl " includes both the future root and stem. The plumule is that part of the embryo between the cotyledons and above their point of attachment to the caulicle. It is the upward growing point of the young plant, and hence the place of attachment of the cotyledon is the first node, or point of leaf origin, on the stem. The epicotyl, in contradistinction to the hypocotyl, is all that part of the plant above the insertion of the cotyledons. Before germination it is identical with the plumule. As the seedling grows, the epicotyl advances its growing point by adding new nodes and internodes, as the spaces between the successive points of leaf insertion are called. 47. Botanical terms. — As the prefixes hypo and epi are of frequent occurrence in botanical works, it will aid in understanding their various compounds if you will remem- ber that hypo always refers to something below or beneath, and epi, to something over or above. With this idea in mind you will see that botanical terms are a labor-saving device, since it is much easier, in making notes, to use a single de- scriptive word than to write out the long English equivalent, such as " the part under (or over) the cotyledons," GERMINATION AND GROWTH 47 Practical Questions 1. Do the cotyledons, as a general thing, resemble the mature leaves of the same plants ? 2. Name some plants in which you have observed differences, and ac- count for them ; could convenience of packing in the seed coats, for in- stance, or of getting out of them, have any bearing on the matter ? 3. Does the position in which seeds are planted in the ground have anything to do with the position of the seedlings as they appear above the surface ? 4. Is this fact of any importance to the farmer ? 5. Will grain that has begun to germinate make good meal or flour? Why? (27,36; Exp. 25.) IV. GROWTH MATERIAL. — Two young potted plants ; some lily or hyacinth bulbs ; seedlings of different kinds, — some with well- developed taproots, — apple, cotton, and maple are good examples. APPLIANCES. — A small flat dish, some mer- cury, and a piece of cork. EXPERIMENT 34. How DOES THE ROOT IN- CREASE IN LENGTH ? — Mark off the root of a very young corn seedling into sections by moistening a piece of sewing thread with indelible ink and applying it to the surface of the root at intervals of about two millimeters (-fa of an inch), or by tying a thread lightly around it at the same inter- vals. Lay the seedling on a moist bedding be- tween two panes of glass kept apart by a sliver of wood to prevent their injuring the root by pressure. Watch for a day or two, and you will see that growth takes place from a point just back of the tip (Figs. 61, 62). Mark off a seedling of the bean in the same way and watch to see whether it increases in the same manner as the corn. EXPERIMENT 35. How DOES THE STEM INCREASE IN LENGTH ? — Mark off a portion of the stem of a bean seedling as explained in the last experi- ment, and find out how it grows. Allow a seedling to develop until it has put forth several leaves and measure daily the spaces between them. Label these spaces in your drawings, " intornodes," and the points where the leaves are attached, " nodes." Does an internode stop growing when the FIGS. 61, 62. — Seed- ling of corn, marked to show region of growth : 61, early stage of germi- nation ; 62, later stage. 48 PRACTICAL COURSE IN BOTANY one next above it has formed ? When is growth most rapid ? Reverse the position of a number of seedlings that have just begun to sprout and watch what will happen. After a few days reverse again and note the effect. 63 64 FIGS. 63, 64.— Root of bean seed- ling, measured to show region of growth : 63, early stage of germina- tion ; 64, later stage. 65 63 FIGS. 65, 66. — Stem of bean seedling, measured to show region of growth : 65, early stage of growth ; 66, later stage. EXPERIMENT 36. CAN PLANTS GROW AND LOSE WEIGHT AT THE SAME TIME ? — Remove the scales from a white lily bulb, weigh them, and lay in a warm, but not too damp place, away from the light. After a time bulblets will form at the bases of the scales. Weigh them again, and if there has been any loss, account for it. The experiment may be tried by allowing a potato tuber or a hyacinth bulb to germinate without absorbing moisture enough to affect its weight. EXPERIMENT 37. Is THE DIRECTION OF GROWTH A MATTER OF ANY IMPORTANCE ? — Plant in a pot suspended as shown in 67 68 Fig. 67, a healthy seedling of some kind, FIGS. 67, 68. — Experiment show- two or three inches high, so that the ing the direction of growth in stems: plumule shall point downward through 67, young potato planted in an in- , . , verted position ; 68, the same after the dram nole and thc root upward into an interval of eight days. the soil. Watch the action of the stem GERMINATION AND GROWTH 49 for six or eight days, and sketch it at successive intervals. After the stem has directed itself well upward, invert the pot again, and watch the growth. After a week remove the plant and notice the direction of the root. Sketch it entire, showing the changes in direction of growth. At the same time that this experiment is arranged, lay another pot with a rapidly growing plant on one side, and every forty-eight hours reverse the position of the pot, laying it on the opposite side. At the end of ten or twelve days remove the plant and examine. How has the growth of root and stem been affected? What do we learn from these experiments and from Exp. 35 as to the normal direction of growth in these two organs respectively? Can you think of any natural force that might influence this direction ? EXPERIMENT 38. To SHOW THAT PLANTS WILL EXERT FORCE RATHER THAN CHANGE THEIR DIRECTION OF GROWTH. — Pin a sprouted bean to a cork and fasten the cork to the side of a flat dish, as shown in Fig. 69. Cover the bottom of the dish with mercury at least half an inch deep, and over the mercury pour a layer of water. Cover the whole with a pane of glass to keep the moisture in, ,_, FIG. 69. — Experiment and leave for several days. The root will force its showing the root of a seed- way downward into the mercury, although the ling forcing its way down- latter is fourteen times heavier than an equal ward throush mercury, bulk of the bean root substance, and the root must thus overcome a resistance equal to at least fourteen times its own weight. 48. What growth is. — With the seedling begins the growth of the plant. Most people understand by this word mere increase in size ; but growth is something more than this. It involves a change of form, usually, but not necessarily, accompanied by increase in bulk. Mere me- chanical change is not growth, as when we bend or stretch an organ by force, though if it can be kept in the altered position till such position becomes permanent, or as we say in common speech, " till it grows that way," the change may become growth. To constitute true growth, the change of form must be permanent, and brought about, or main- tained, by forces within the plant itself. 49. Conditions of growth. - - The internal conditions de- pend upon the organization of the plant. The essential external conditions are the same as those required for germi- 50 PRACTICAL COURSE IN BOTANY nation : food material, water, oxygen, and a sufficient degree of warmth. It may be greatly influenced by other circumstances, such as light, gravitation, pressure, and (probably) electricity ; but the four first named are the essen- tial conditions without which no growth is possible. 50. Cycle of growth. — When an organ becomes rigid and its form fixed, there is no further growth, but only nutri- tion and repair, — processes which must not be confounded with it. Every plant and part of a plant has its period of beginning, maximum, decline, and cessation of growth. The cycle may extend over a few hours, as in some of the fungi, or, in the case of large trees, over thousands of years. 51. Geotropism. - - The general tendency of the growing axes of pknts to take an upward and downward course as shown in Exp. 37 — in other words, to point to and from the center of the earth — is called geotropism. It is positive when the growing organs point downward, as most primary roots do ; negative when they point upward, as in most primary stems ; and transverse, or lateral, when they extend horizon- tally, as is the case with most secondary roots and branches. 52. Gravity and growth. — It cannot be proved directly that geotropism is due to gravity, because it is not possible to remove plants from its influence so as to see how they would behave in its absence. The effect of gravity may be neutralized, however, by arranging a number of sprouting seeds on the vertical disk of a clinostat, an instrument fitted with a clockwork movement by means of which they may be kept revolving steadily for several days. By this constant change of position gravity is made to act on them in all directions alike, which is the same in some respects as if it did not act at all. As the roots, under these circum- stances, turn their growing tips toward the axis of motion, without showing a tendency to grow downward, we may con- clude that geotropism is a response of the plant to gravity. 53. Geotropism an active force. — It must be noted, however, that the force here alluded to is not the mere me- GERMINATION AND GROWTH 51 chanical effect of gravity, due to weight of parts, as when the bough of a fruit tree is bent under the load of its crop, but a certain stimulus to which the plant reacts by a spontaneous adjustment of- its growing parts. In other words, geotro- pism is an active, not a passive function, and the plant will overcome considerable resistance in response to it. (Exp. 38). 54. Other factors. - - The direction of growth is influ- enced by many other factors, such as light, heat, moisture, contact with other bodies, electricity. The result of all endless variety in the forms organs that seems to defy Heat, unless excessive, gen- growth ; contact sometimes causing the stem to curve turbing object, and sometimes the stem to curve toward the by growing more rapidly on and perhaps by these forces is an and growth of all law. erally stimulates stimulates it, away from the c 1 i s- retards it, causing object of contact the opposite side, FIG. 70. — A piece of a haulm of millet that has been laid horizontally, righting itself through the combined influence of contact and negative geotropism. as in the stems of twining vines. Light stimulates nutrition, but generally retards growth. The movements of plants toward the light are effected in this way; growth being checked on that side, the plant bends toward the light. Practical Questions 1. Why do stems of corn, wheat, rye, etc., straighten themselves after being prostrated by the wind ? (51, 54.) 2. Do plants grow more rapidly in the daytime, or at night ? (54.) 3. Reconcile this with the fact that green plants will die if deprived of light. 52 PRACTICAL COURSE IN BOTANY 4. Which grows more rapidly, a young shoot or an old one ? (31, 50.) 5. Which, as a general thing, are the more rapid growers, annuals or perennials ? Herbaceous or woody-stemmed plants ? 6. Name some of the most rapid growers you know. 7. Of what advantage is this habit to them ? 8. Why do roots form only on the under side of subterraneous stems ? (51.) 9. Why do new twigs develop most freely on the upper side of hori- zontal branches ? (51.) Field Work (1) Notice the various seedlings met with in your walks and see how many you can recognize by their resemblance to the mature plants. Ac- count for any differences you may observe between seedlings and older plants of the same species. Observe the cotyledons as they come up and their manner of getting out of the ground, and notice the ways in which this is influenced by moisture, light, and the nature of the soil. Where the cotyledons do not appear, dig into the ground and find out the reason. Notice which method of emergence occurs in each case, the arched, or straight, and account for it. Observe particularly the behavior of seed- lings in hard, sunbaked soil. If you see any of them lifting cakes of earth, compare the size and weight of the cake with that of the seed ; if there is any disparity, what does this imply ? What is the force called which the plant exercises in lifting the weight? (51.) (2) Notice if there are any seeds germinating successfully on top of the ground, and find out by what means their roots get into the soil. Observe what effect sun and shade, moisture and drought, and the nature of the soil have on the process. Find out whether roots exercise force in penetrating the soil ; what kinds they penetrate most readily, and what kinds, if any, they fail to penetrate at all. Notice whether seedlings with taproots, like the turnip and castor bean, or those with fibrous roots, like corn and wheat, are more successful in working their way downward. (3) Look for tree seedlings. Explain why seedlings of fruit trees are so much more widely distributed in cultivated districts, and so much easier to find than those of forest trees. Where do the latter occur, as a general thing? Account for the fact that seedling trees are so much more rare than germinating herbs, and why trees like the oak and chestnut and black walnut propagate so much more slowly, in a state of nature, than the pine, cedar, ash, and maple. (4) Observe the direction of growth in plants on the sides of gullies and ravines, and tell how it is influenced by geotropism. Notice whether there are other influences at work ; for instance, light, or in the case of roots, the attraction of moisture. CHAPTER III. THE ROOT I. OSMOSIS AND THE ACTION OF THE CELL MATERIAL. — For experiments in osmosis provide fresh and boiled slices of red beet, a fresh egg, a piece of ox bladder or some parchment paper; glass tubing, thread, twine, elastic bands, salt and sugar solutions. A common medicine dropper with the small end cut off will answer instead of tubing for making an artificial cell; or an eggshell may be used, by blowing out the contents through a puncture in the small end, and care- fully chipping away a portion of the shell at the big end, leaving the lining membrane intact. The different liquids can be put into the shell and the exposed membrane placed in contact with the liquid in the glass, by fitting over the latter a piece of card- board with a hole in the center large enough for the exposed surface to protrude sufficiently to touch the water. 55. Object of the experiments. — In or- der to understand clearly the action of roots in absorbing moisture from the soil, it will be necessary to learn something about the movement of liquids through the cells, upon which the physiological processes of the plant depend. For this purpose make an artificial cell by tying a piece of ox bladder or parchment paper tightly over one end of a small glass tube, as shown in Fig. 71. EXPERIMENT 39. How DOES ABSORPTION TAKE PLACE IN THE CELL ? — (a) Put some salt water in a wineglass, partly fill the tube of the artificial cell with fresh water, and mark on the outside of both vessels the height at which the contained liquid stands. Set the tube in the glass of saltwater and wait for results, having first tested care- fully to make sure that there are no leaks in the membrane. After half an hour, notice whether there is any increase of water in the glass, as indicated by the mark. If so, where did it come from ? Is there any loss 53 FIG. 71.— Artificial cell. 54 PRACTICAL COURSE IN BOTANY of water in the tube ? What has become of it ? How did it get out ? Taste it to see if any of the salt water has got in. Which is the heavier, salt water, or fresh ? (If you do not know, weigh an equal quantity of each.) In which direction did the principal flow take place; from the heavier to the lighter, or from the lighter to the heavier liquid ? (6) Put a sugar or salt solution in the tube, and clear, fresh water in the glass, marking the height in each as before. Does the liquid rise or fall in the tube ? Does any of it escape into the water of the glass, and if so, is it more or less than before ? Which now contains the denser fluid, the tube or the glass ? What principle governs the course of the liquid ? Try the same experiment with (c), the same liquid in both vessels, and notice whether there is a greater flow in one direction than the other, as indicated by a comparison with the marks on the outside, (d) Put in the tube some of the white of a raw egg, insert in a glass of pure water, and note the effect, (e) Reverse, with water in the tube and white of egg in the glass. Does the water rise in the tube as before ? Test the contents for proteins ; has any of the albumin passed through the membrane into the tube? EXPERIMENT 40. To TEST THE BEHAVIOR OF LIVING AND DEAD CELLS. — Slice a fresh piece of red beet into a vessel of water and of a boiled one into another vessel of the same liquid at the same temperature. What differ- ence do you notice ? Can you think of any reason why the boiled one gives up its juices and the other one does not ? 56. Osmosis. - - The passage of liquids through mem- branes is known as osmosis. Our experiments have shown that the principles governing the osmotic movement are : (1) the flow of the thinner and lighter liquid toward the denser and heavier takes place more rapidly than in the opposite direction ; (2) the rapidity of the flow depends on the difference in density; (3) solutions of crystallized sub- stances, like sugar and salt, osmose readily ; (4) albuminous substances, such as the white of an egg, osmose so slowly that the cell wall may be regarded as practically imperme- able to them. 57. Osmosis a form of diffusion. — Osmosis is related to diffusion as a part to the whole. In other words, it is a name given to the process when it takes place through a membrane, whether solid, as the outer wall of the cell, or fluid, as the inner wall of living protoplasm. Diffusion may THE ROOT 55 take place without osmosis, — for example, when we sweeten our te.a or coffee by allowing sugar to diffuse through it. It may also take place through the cell wall in connection with the osmotic current ; or substances may diffuse into or out of the cell independently of osmosis. For this reason it is not safe to rely on the evidence of differently colored or differently tasting liquids in making experiments, unless we are sure of the osmotic properties of the solution, as the contained substances may diffuse through the membranes even though no interchange of liquids is going on at the time. 58. Absorption in living and dead cells. - - There is one great difference between the action of the artificial cell used in the foregoing experiments and that of the cells of which a living body is built up. The former contains no proto- plasm, and the osmosis is a purely mechanical process depend- ing on the nature of the liquids, or possibly on some physical property of the membrane. Any substance to which the membrane is permeable can pass through. In the living cell the protoplasm exercises a power of absorption independent of the cell wall, sometimes rejecting substances admitted by the latter, sometimes retaining others to which it is perme- able, as shown in Exp. 40. In the boiled beet the protoplasm had been killed and the red coloring matter passed through it unhindered, while in the living one it was held back by the protoplasmic lining, which is thus seen to control the absorptive properties of the cell. 59. Plasmolysis. — Cells can be killed or injured in other ways than by heat ; for example, by cold, by poisons, by starvation, and by overfeeding through the use of too much fertilizer or too rich a one. In this last case, the soil water becomes impregnated with soluble matter from the manure, which may render it denser than the sap in the roots. When this happens, it will cause the osmotic flow to set outward and thus deplete the cell of its contents ; whence we have the paradox that a cell, or even a whole plant, may be starved 56 PRACTICAL COURSE IN BOTANY by overfeeding. This action of osmosis in withdrawing the contents from a cell is termed plasmolysis, and you can easily understand how very important a knowledge of the principles governing it is to the farmer in determining the application of fertilizers to his crops. Dead cells, although powerless to carry on the life processes of a plant, have nevertheless important uses in serving the purposes of mechanical support and also to some extent in assisting in the work of absorption, though their function here is a purely mechanical one. 60. Selective absorption. — Different plants through their roots absorb different substances from the soil water, or the same substance in varying degrees. Hence, one kind of crop will exhaust the soil of certain minerals while leav- ing other kinds in- tact, or very little diminished; and vice versa, another kind will take up abun- dantly what its pred- ecessor has rejected. In this sense, plants are said to exercise a selective power in the absorption of nu- trients. The expres- sion must not be understood, however, as implying any kind of volitional discrimination. It is merely a short and con- venient way of saying that the cells of different plants possess different degrees of permeability to certain substances, some being more permeable to one thing, some to another. But beyond this rejection of untransmissible substances there is no FIG. 72. — Root absorbing mineral food from rock. The large sycamore, whose base is partly con- cealed by the trumpet creeper on the left of the pic- ture, is growing in very hard, stony soil, and one of its main roots has molded itself so completely to the ledge of rock protruding on the right, that when a portion of it was torn away, as shown where the light streak ends at a, the impress of its fibers was so strongly marked on the rock as to give the latter the appearance of a petrified root. THE ROOT 57 active power of discrimination, any substance that can pass through the cell wall and its protoplasmic lining being taken in, whether useful, unnecessary, or even harmful. The last two may be got rid of by excretion, as the superfluous water taken in with dissolved minerals is exhaled from the leaves ; or if incapable of passing out by osmosis, rendered harmless and retained in the form of the curious " crystalloids" found in various parts of plants. But while the kind of selection exercised by vegeta- ble cells implies no power of choice, as a matter of fact those substances most used by the plant in carrying on its life processes are ab- sorbed in much greater quantities than others, being transferred to parts where growth or other changes in the plant tissues are gO- FIG. 73. — Roots of elm and sycamore contending for inff on and thprp P°ssessi°n of the soil on a rocky bluff on the Potomac. used up in the work of nutrition, or excreted in part as waste products. In either case their passage from cell to cell will give rise to a continuous osmotic current in that direction, and the absorption of new matter will go on in proportion to the amounts used up. 61. Definition. -- Tissue is a word used to denote any animal or vegetable substance having a uniform structure organized to perform a particular office or function. Thus, 58 PRACTICAL COURSE IN BOTANY for instance, we have bony tissue and muscular tissue in animals ; that is, tissue made of bone substance and muscle substance and doing the work of bone and muscle respec- tively. Likewise in plants, we have strengthening tissue made up of hard, thick-walled cells, serving mainly for pur- poses of mechanical support, and vascular tissue, made up of conducting vessels for conveying sap — and so on, for every separate function. ' Practical Questions 1. Why do raspberries and strawberries have a flabby, wilted look if sugar has been put on them too long before they are served ? (7, 56.) 2. Where has the juice gone ? What caused it to go out of the berries ? (56, 59.) 3. Is a knowledge of the principles governing osmosis of any practical use to the housekeeper ? 4. Why cannot roots absorb water as freely in winter as in summer? (Suggestion : which is the heavier, cold or warm water ? ) 5. Why does fertilizing too heavily sometimes injure a crop? (59.) 6. Do you see any apparent contradiction between the action of plas- molysis and the selective power of protoplasm ? Can you reconcile it ? 7. If a piece of beet that has been frozen is placed in water it will be- have just as the slice of boiled beet did in Exp. 40 ; explain. (58, 59.) II. MINERAL NUTRIMENTS ABSORBED BY PLANTS MATERIAL. — A dozen or two each of different kinds of seeds and grains. A small portion from a growing shoot of a woody and a herbaceous land plant, and of some kind of succulent water or marsh plant, such as arrow grass (Sagittaria) , water plantain, etc. APPLIANCES. — A pair of scales ; a lamp, stove, or other means of burn- ing away the perishable parts of the specimens to be studied. EXPERIMENT 41. — Do THE TISSUES OF PLANTS CONTAIN MINERAL MATTER ? — Take about a dozen each of grains and seeds of different kinds, weigh each kind separately, and then dry them at a high temperature, but not high enough to scorch or burn them. After they have become perfectly dry, weigh them again. What proportion of the different seeds was water, as indicated by their loss of weight in drying ? Burn all the solid part that remains, and then weigh the ash. What proportion of each kind of seed was of incombustible material? What proportion of the solid material was destroyed by combustion ? THE ROOT 59 EXPERIMENT 42. — Do THEY CONTAIN DIFFERENT KINDS AND QUANTI- TIES OF MINERALS ? — Test in the same way the fresh, active parts of any kind of ordinary land plant (sunflower, hollyhock, pea vines, etc.), and of some kind of succulent water or marsh plant (Sagittaria, water lily, fern). Do you notice any difference in the amount of water given off and of solid matter left behind ? In the character of the ashes left ? Have you observed in general any difference between the ashes of different woods ; as, for instance, hickory, pine, oak ? Compare with the residue left in Exp. 21 ; would you judge that the residual substances are of the same composition ? 62. Essential constituents. -- The composition of the ash of any particular plant will depend upon two things : the absorbent capacity of the plant itself and the nature of the substances con- tained in the soil in which it grows. But chemical analysis has shown that how- ever the ashes may vary, they always contain some proportion of the follow- ing substances : potassium (potash), calcium (lime), magnesium, phosphorus, and (in green plants) iron. These ele- ments occur in all plants, and if any one of them is absent, growth becomes ab- normal if not impossible. The part of the dried substances that was burned away after expelling the Water Consists, in all plants, mainly of different food elements: iii •, i 1, with all the elements; carbon, hydrogen, oxygen, nitrogen, and 2, without potassium ; 3, sulphur, in varying proportions. These with soda instead of pot- ash ; 4, without calcium ; five rank first in importance among the 5, without nitrates or am- essential elements of vegetable life, and monia salts- without them the plant cell itself, the physiological unit of vegetable structure, could not exist. They compose the greater part of the substance of every plant, carbon alone usually forming about one half the dry weight. Other sub- stances may be present in varying proportions, but the two groups named above are found in all plants without excep- 42135 FIG. 74.— Water cul- 60 PRACTICAL COURSE IN BOTANY tion, and so we may conclude that (with the possible addition' of chlorine) they form the indispensable elements of plant food. Carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus compose the structure of which the plant is built. The other four ingredients do not enter into the substance as component parts, but aid in the chemical processes by which the life functions of the plant are carried on, and are none the less essential elements of its food. Figure 74 shows the difference between a plant grown in a solution where all the food elements are present, and others in which some of them are lacking. 63. How plants obtain their food material. — Plants obtain their supply of the various mineral salts from solu- tions in the soil water which they absorb through their roots. With a few doubtful exceptions, they cannot as- similate their food unless it is in a liquid or gaseous form. Of the gases, carbon dioxide, oxygen, and hydrogen can be freely absorbed from the air, or from water with va- rious substances in solution, but most plants are so con- stituted that they cannot absorb free nitrogen from the air ; they can take it only in the form of compounds from nitrates dissolved in the soil, and hence the importance of ammonia and other nitrogenous compounds in artificial fertilizers. Some of the pea family, however, bear on their roots little tubers formed by minute organisms called bacteria, which have the power of extracting nitrogen directly from the free air mingled with the soil ; and hence the soil in which these tuber-bearing legumes decay is enriched with nitrogen in a form ready for use. FIG. 75. — Roots of soy bean bearing tubercle-forming bacteria. THE ROOT 61 Practical Questions 1 . Could any normal plant grow in a soil from which nitrogen was lack- ing? Potash? Lime? Phosphorus? (62.) 2. Could it live in an atmosphere devoid of oxj^gen ? Nitrogen ? Car- bon dioxide? (62.) ^ 3. Why are cow peas or other legumes planted on worn-out soil to renew it? (63.) 4. Is the same kind of fertilizer equally good for all kinds of soil ? For all kinds of plants ? (60, 62.) 5. Why does too much watering interfere with the nourishment of plants? (Exps. 26, 27.) 6. Are ashes fit for fertilizers after being leached for lye? (62.) 7. Why will plants die, or make very slow growth, in pots, unless the soil is renewed occasionally? (60, 62.) III. STRUCTURE OF THE ROOT MATERIAL. — Taproot of a young woody plant not over one or two years old ; apple and cherry shoots make good specimens. For showing root hairs, seedlings of radish, turnip, or oat are good, also roots of wan- dering Jew grown in water ; for the rootcap, corn, sunflower, squash. 64. Gross anatomy of the root. — Cut a cross section of any woody taproot, about halfway between the tip and the ground level, examine it with a lens, and sketch. Label the dark outer covering, epidermis, the soft layer just within that, cortex, the hard, woody axis that you find in the center, vas- cular cylinder, and the fine sil- very lines that radiate from the center to the cortex, medullary rays (in a very young root theec will not appear) . Cut a section through a root that has stood in coloring fluid for about three hours and note the parts colored by the fluid. What portion of FIG. 76. — Cross section of a young , i -, i • i /. taproot ; a, a, root hairs ; b, epider- the rOOt, WOUld yOU judge from mis ; c, cortical layer ; d, fibro vascular this, acts as a Conductor Of the cylinder. Note the absence of med- ullary rays during the first year of water absorbed from the ground r growth. 62 PRACTICAL COURSE IN BOTANY Make a longitudinal section passing through the central portion of the root and extending an inch or two into the lower part of the stem. Do you find any sharp line of divi- sion between them? Notice the hard, woody axis that runs through the center. This is the vascular cylinder and con- tains the conducting vessels, the cut ends of which were shown in cross section in Fig. 76. 65. Distinctions between root and stem. — Pull off a branch from the stem and one from the root ; which comes off the more easily ? Examine the points of attachment of the two and see why this is so. This mode of branching from the central axis instead of from the external layers, as in the stem, is one marked distinction be- tween the structure of the two organs. In stems, moreover, branches occur normally section of branching above the points of leaf insertion at the root, showing the branches, n, n, origi- nodes (46), while in the root they tend to nating in the central arrange themselves in straight vertical rows. The shoots and cions that often originate from them are not normal root branches, but outgrowths from irregular or adventitious buds, that may occur on any part of a plant. The root is not divided into nodes like the stem, and never bears leaves. 66. The active part of the root. — It is only the newest and most delicate parts of the root that pro- duce hairs and are engaged in the active work of absorp- tion, the older parts acting mainly as carriers. Hence, old roots lose much of their characteristic structure and , FIG. 78. — Root of a tree on the side of take on more ana more 01 a guiiey, acting as stem. FIG. 77. — Verti- axis, /, and passing through the cortex, r, r. THE ROOT 63 the office of the stem, until there is practically no difference between them. On the sides of gullies, where the earth has been washed from around the trees, we often see the upper portion of the root covered with a thick bark and ful- filling every office of a true stem. 67. Minute structure of the root. — (a) Mount in water and place under the microscope a portion of the root of an oat or radish seedling containing a number of hairs. In studying the thin, transparent roots of very young seedlings a section will not be necessary. Observe whether the hairs originate from the epidermis or from the interior. Are they true roots, or mere outgrowths from h' the cells of the epidermis? Do they consist of a single cell or a number of cells each? Notice what very thin cell walls the hairs have ; is there any advan- tage in this ? The interior, trans- parent portion of the hair con- tains the sap, and the protoplasm forms a thin lining on the inner FlG 79 _ Longitudinal section Surface of the Wall; why not through the tip of a young root, some- .. , , what diagrammatic : h, h, root hairs ; the Sap next the Wall and tile epj epidermis; a, cortex; b, central cylinder; e, sheath of the cylinder (endodermis) ; g, growing point ; c, root cap ; d, dead and dying cells loos- ened from the extremity of the cap. protoplasm in the interior ? (58, 60.) (b) Next examine a portion of the body of the root and try to make out the parts as shown in Fig. 79, and compare them with your observa- tions in 64. The light line running through the middle is the central cylinder, up which the water passes, as was shown by the colored liquid in 64. Outside this is a darker por- tion (a, Fig. 79), corresponding to the cortex (rr, Fig. 77). Besides other uses, the cortex serves to prevent the loss of water as it passes up to the stem, and also, in fleshy roots like the carrot and turnip, for the storage of nourish- 64 PRACTICAL COURSE IN BOTANY ment. Its innermost row of cells is thickened into the sheath, or endodermis (e), which serves as an additional protection to the conducting tissues. The extreme outer layer, from the cells of which the root hairs are developed, is, as already stated, the epidermis, and in the older and more exposed parts of perennial roots is displaced by the bark, which becomes indistinguishable from that of the stem. (66.) (c) Look at the tip of the root for a loose structure (c) fitting over it like a thimble. This is the rootcap. Do you see any loose cells that seem to have broken away from it ? These are old cells that have been pushed to the front by the formation of new growth back of them, and, being of no further use, are rubbed off by friction as the root bores its way through the soil. Draw a longitudinal section of the root as it appears under the microscope, labeling all the parts. If they cannot be made out distinctly in the specimen exam- ined, use sections of young corn or bean roots, which are larger and show the parts more distinctly. (d) Place under the microscope a thin cross section through the hairy portion of a primary root of a bean or pea seedling, and try to make out the parts noted above and shown in cross section in Fig. 80. Make a sketch of what you see, labeling all the parts you can recognize. Show in your drawing the differences in the size and shape of the cells composing the different tissues. No- tice in the central cylinder (jij gQ) several groUpS of 5 r what look in the section like little round pits, or holes, sp. These are the cut ends of large-sized tubes or ducts that convey the water absorbed FIG. 80. — Cross section of a young root, magnified : h, hairs ; a, cortex ; b, central cylinder ; c, sheath or endodermis ; ep, epi- dermis ; sp, cut ends of the ducts. THE ROOT 65 by the roots to the stem. Each set of these tubes, together with a number of smaller ones belonging to the same group, constitutes a fibrovascular bundle — a very important ele- ment in the structure of all roots and stems, as these bundles make up the conducting system of the plant body. IV. THE WORK OF ROOTS MATERIAL. — Germinating seedlings of radish, bean, corn, etc. ; a potted plant of calla, fuchsia, tropseolum, touch-me-not (Impatiens), or corn; a plant that has been growing for some time in a porous earthen jar. APPLIANCES. — Glass tumblers ; coloring fluid ; wax ; some coarse net- ting; dark wrapping paper, or a long cardboard box; a sheet of oiled paper ; some half-inch glass tubing ; a few inches of rubber tubing ; an ounce of mercury ; some blue litmus paper ; a flower pot full of earth ; a few handfuls of sand, clay, and vegetable mold; a pair of scales; a half dozen straight lamp chimneys, or long-necked bottles from which the bottoms have been removed as directed in Exp. 53. EXPERIMENT 43. USE OF THE EPIDERMIS. — Cut away the lower end of a taproot; seal the cut surface with wax so as to make it perfectly water-tight, and insert it in red ink for at least half the remaining length, taking care that there is no break in the epidermis. Cut an inch or two from the tip of the lower piece, or if material is abundant, from another root of the same kind, and without sealing the cut surface, insert it in red ink, beside the other. At the end of three or four hours, examine longitu- dinal sections of both pieces. Has the liquid been absorbed equally by both ? If not, in which has it been absorbed the more freely ? What con- clusion would you draw from this, as to the passage of liquids through the epidermis? From this experiment we see that the epidermis, besides protecting the more delicate parts within from mechanical injury by hard substances contained in the soil, serves by its comparative imperviousness to prevent evaporation, or the escape of the sap by osmosis as it flows from the root hairs up to the stem and leaves. EXPERIMENT 44. To SHOW THAT ROOTS ABSORB MOISTURE. — Fill two pots with damp earth, put a healthy plant in one, and set them side by side in the shade. After a few days examine by digging into the soil with a fork and see in which pot it is drier. Where has the moisture gone ? How did it get out ? 66 PRACTICAL COURSE IN BOTANY EXPERIMENT 45. To SHOW THAT ROOTS SHUN THE LIGHT. — Cover the top of a glass of water with thin netting, arid lay on it sprouting mustard or other convenient seed. Allow the roots to pass through the netting into the water, noting the position of root and stem. Envelop the sides of the glass in heavy wrapping paper, admitting a little ray of light through a slit in one side, and after a few days again observe the relative position of the two organs. How is each affected by the light ? EXPERIMENT 46. To FIND OUT WHETHER ROOTS NEED AIR. — Remove a plant from a porous earthenware pot in which it has been growing for some time ; the roots will be found spread out in contact with the walls of the pot instead of embedded in the soil at the center. Why is this ? EXPERIMENT 47. To SHOW THAT ROOTS SEEK WATER. — Stretch some coarse netting covered with moist batting over the top of an empty tumbler. Lay on it some seedlings, as in Exp. 45, allowing the roots to pass through the meshes of the netting. Keep the batting moist, but take care not to let any of the water run into the vessel. Observe the position of the roots at intervals, for twelve to twenty-four hours, then fill the glass with water to within 10 millimeters (a half inch, nearly) or less of the netting, let the batting dry, and after eight or ten hours again observe the position of the roots. What would you infer from this experiment as to the affin- ity of roots for water ? EXPERIMENT 48. WHAT BECOMES OF THE WATER ABSORBED BY ROOTS. — Cover a calla lily, young cornstalk, sunflower, tropseolum, or other succulent herb with a cap of oiled paper to prevent evaporation from the leaves, set the pot containing it in a pan of tepid water, and keep the tem- perature unchanged. After a few hours look for water drops on the leaves. Where did this water come from ? How did it get up into the leaves ? EXPERIMENT 49. To SHOW THE FORCE OF ROOT PRESSURE. — Cut off the stem of the plant 6 or 8 centimeters (3 or 4 inches) from the base. Slip over the part remaining in the soil a bit of rubber tubing of about the same diameter as the stem, and tie tightly just below the cut. Pour in a little water to keep the stem moist, and slip in above, a short piece of tightly fitting glass tubing. Watch the tube for several days and note the rise of water in it. The same phenomenon may be observed in the " bleeding " of rapidly growing, absorbent young shoots, such as grape, sunflower, gourd, tobacco, etc., if cut off near the ground in spring when the earth is warm and moist. By means of an arrangement like that shown in Fig. 81, the force of the pressure exerted can be measured by the dis- placement of the mercury. This flow cannot be due to the giving off of moisture by the leaves, since they have been removed. Their action, when present, by causing a deficiency of moisture in certain places may THE ROOT 67 influence the direction and rapidity of the current, but does not furnish the motive power, which evidently comes, in part at least, from the roots, and is the expression of their absorbent activity. EXPERIMENT 50. To SHOW THAT ROOTS GIVE OFF ACIDS. — Lay a piece of blue lit- mus paper on a board or on a piece of glass slightly tilted at one end to secure drainage. Cover the surface with an inch of moist sand and plant in it a number of healthy seedlings. Acids have the property of changing blue litmus to red ; hence, if you find any red stains on the paper where the roots have penetrated, what are you to conclude ? The kind of acid given off may differ ac- cording to the soil the roots are growing in and the solutions it contains. Carbon dioxide has a slight acid reaction and is exhaled in varying quantities by all roots. EXPERIMENT 51. CAN THE ABSORBENT POWER OF ROOTS BE INTERFERED WITH ? — Place the roots of a number of seedlings with well-developed hairs in a weak solution of saltpeter — 10 grams (about £ of an ounce) to a pint of water, and others in a stronger solution — say 30 grams, or 1 ounce, to a pint. Try the same experiment with weak and strong solutions of any conveniently obtainable liquid fertilizer. After 45 minutes or an hour examine the roots under a lens and note the change that has taken place. What has gone out of them ? What caused the loss of the contained sap ? EXPERIMENT 52. To TEST THE WEIGHT OF SOILS. — Thoroughly dry and powder a pint each of sand and clay, measure accurately, and balance against each other in a pair of scales. Which weighs more, bulk for bulk, a "light" soil, or a "heavy" one? EXPERIMENT 53. To TEST THE CAPACITY OF SOILS FOR ABSORBING AND RETAINING MOISTURE. — Arrange, as shown in Fig. 82, a number of long- necked bottles from which the bottom has been removed. This can be done by making a small indentation with a file at the point desired and leading the break round the circumference with the end of a glowing wire or a red-hot poker. The crack will follow the heated object with sufficient FIG. 81. — Arrangement for estimating the force of root pres- sure : s, stub of the cut stem ; g, glass tubing joined by means of the rubber tubing, t, to the stem ; ra, mercury forced up the glass tube by water, w, pumped from the soil by the roots. 68 PRACTICAL COURSE IN BOTANY regularity to answer the purpose. Tie a piece of thin cloth over the mouth of each bottle and invert with the necks extending an inch or two into empty tumblers placed beneath. Fill all to the same height with soils of different kinds — sand, clay, gravel, loam, vegetable mold, etc. — and pour FIG. 82. — Apparatus for testing the capacity of soils to take in and retain moisture. over each the same quantity of water from above. Watch the rate at which the liquid filters through into the tumblers. Which loses its mois- ture soonest ? Which retains it longest ? Next leave the soils in the bottles dry, fill the tumblers up to the necks of the bottles, and watch the rate at which the water rises in the different ones. The power of soils to absorb moisture is called capillarity. Which of your samples shows the highest capillarity ? Which the lowest ? Do you observe any relation between the capillarity of a soil and its power of retention ? 68. Roots as holdfasts. — One use of ordinary roots is to serve as props and stays for anchoring plants to the soil. Tall herbs and shrubs, and vegetation generally that is exposed to much stress of weather, are apt to have large, strong roots. Even plants of the same species will develop systems of very different strength according as they grow in sheltered or exposed places. THE ROOT 69 a b FIG. 83. — Dandelion : a, common form, grown in plains region at low altitude ; b, alpine form. 69. Root pull. — Roots are not mere passive holdfasts, but exert an active downward pull upon the stem. Notice the rooting end of a strawberry or raspberry shoot and observe how the stem appears to be drawn into the ground at the rooting point. In the leaf ro- settes of herbs growing flat on the ground or in the crevices of walls and pavements, the strong depression observable at the center is due to root pull. (Fig. 84.) 70. Storage of food. — Another of- fice of roots is to store up food for the use of the plant. This is done chiefly in the tissues of fleshy roots and tu- bers, and gives to them their great economic value. Next to grains and cereals, roots probably furnish a larger portion of food to the human race than any other crop. In addition to this they are also the source of valu- able drugs, condiments, and dyes. 71. Absorption and conveyance of sap. — But the most important func- tion of roots is that of absorption. By their action the soil water and the minerals contained in it are drawn up into the plant body and made avail- able f or conversion by the leaves into organic foods, as will be explained in another chapter. From the nature of their function, most roots have naturally a FIG. 84. — Raspberry sto- lon showing root pull. 70 PRACTICAL COURSE IN BOTANY strong affinity for water, and its presence or absence has a marked influence on their direction of growth, being often sufficient to overcome that of geotropism (Exp. 47). There are many trees and shrubs, notably willow, sweet bay, red birch, and the like, that grow best on the banks of streams and ponds, where their roots can have direct access to water. Excess of moisture, however, is injurious to most land plants by preventing the roots from getting sufficient air for res- piration. 72. The conditions of absorption. -- The sap in the root cells is normally denser than the water in the soil, so there is* a continuous flow from the latter to the former. But if, for any reason, the density of the liquids should be reversed, the flow would set in the opposite direction, and if continued long enough, the strength of the plant would be literally " sapped " by the exhaustion of its tissues, so that it would die. What is this process of cell exhaustion called ? 73. The use of acid secretions to the root. — It was shown in Exp. 50 that roots give off carbon dioxide, which has a slight acid reaction, and possibly other acids. These chemicals are ac- tive agents in dissolving the various mineral mat- ters contained in the soil, and as these last can be absorbed only in a liquid or a gaseous state (63), the advantage to the root as an absorbent or- gan, of being able to se- crete such active sol- vents, is obvious. 74. Relation of roots to the soil. — In order to FIG. 85. — A natural root etching, found on a piece of slate. perform their work of ab- THE ROOT 71 sorption, roots must have access to a suitable soil. To pro- duce the best results a soil must contain (1) all the essential mineral constituents (62) ; (2) moisture for dissolving these materials ; and (3) air enough to supply the oxygen which is necessary to the life processes of all green plants. 75. Composition of soils. — Sand, clay, and humus, or vegetable mold, with the various substances dissolved in them, constitute the basis of cultivated soils. A mixture of sand, clay, and humus is called loam. When the propor- tion of humus is very large and well decomposed, the mixture is called muck. Pure sand contains but little nourishing matter and is too porous to retain water well. Pure clay is too compact to be easily permeable to either air or water. Most soils are composed of a mixture of the two with vege- table mold in varying proportions, giving a sandy loam, or a clay loam, as the case may be. 76. Tillage. -- The advantages of tillage are: (a) that by breaking up the hard lumps it renders the soil more per- meable to air and water and more easily penetrable by the roots in their search for food ; (b) the covering of loose, friable earth left by the plow and the harrow acts as a mulch, and by shading the soil below, prevents too rapid a loss of water by evaporation. Where the essential food ingredients are present, good tillage counts for more in making a crop than the original quality of the soil. 77. Light and heavy soils. - - These terms are used by farmers not in relation to the weight of soils, but in reference to the ease or difficulty with which they are worked. Light soils contain a preponderance of sand ; heavy ones, of clay. Practical Questions 1, Will plants grow better in an earthen pot or a wooden box than in a vessel of glass or metal? Why? (Exp. 46.) 2. Which absorb more from the soil, plants with light roots and abun- dant foliage, or those with heavy roots and scant foliage ? (Suggestion: roots absorb from the soil ; leaves, mainly from the air.) 72 PRACTICAL COURSE IN BOTANY 3. Why are willows so generally selected for planting along the borders of streams in order to protect the banks from washing ? (71.) 4. Why are the conducting tissues of roots at the center instead of near the surface as in stems? (67, 6.) 5. Why does corn never grow well in swampy ground ? (74; Exp. 46.) 6. Why are fleshy roots so much larger in cultivated plants than in wild ones of the same species? (74, 76.) 7. When the use of a particular kind of fertilizer causes the leaves of the plants to which it has been applied to turn brown, so that the farmer says they have been " burned " by it, to what cause is the trouble due? (59,72.) 8. Why do farmers speak of turnips and other root crops as "heavy feeders"? (70,71.) 9. Which is more exhausting to the soil, a crop of beets, or one of oats ? Onions, or green peas? (See 2, suggestion.) 10. Why will inserting the end of a wilted twig in warm water some- times cause it to revive? (Exps. 48, 49.) V. DIFFERENT FORMS OF ROOTS MATERIAL. — Examples of taproots : bean, pea, cotton, maple seedlings, or any kind of very young woody root. Fibrous : any kind of grass or grain. Fleshy : parsnip, turnip, carrot, dahlia, sweet potato. Water : duckweed, pondweed, or a cutting of wandering Jew grown in water. Parasitic : mistletoe, dodder, beech drops. Aerial and adventitious : the aerial roots of old scuppernong vines, climbing roots of ivy and trumpet vine, prop roots from the lower nodes of cornstalks and sugar cane. 78. Basis of distinction. — Roots vary in form and ex- ternal structure according to their origin, function, and surroundings. In reference to the first, they are classed as primary or secondary ; in regard to the second, as dry or fleshy; while as to surroundings, they may be adapted to either the soil, water, air, or the parasitic habit. Soil roots are the normal form. According to their mode of growth they are either fibrous or axial. 79. Taproots. - - These are the common form of the axial type. Compare the root of any young hardwood cion a year or two old with one of a mature stalk of corn or other grain, and with the roots of seedlings of the same species. Notice the difference in their mode of growth. In THE ROOT 73 PLATE 3. — Aerial roots of a Mexican "strangling" fig, enveloping the trunk of a palm (From " Rep't. Mo, Bot. Garden"). 74 PRACTICAL COURSE IN BOTANY FIG. 86. -Branched tap- the first kind a single stout prolongation called a taproot proceeds from the lower end of the hypocotyl and continues the axis of growth straight downward, unless turned aside by some external influence. A taproot may be either simple, as in the turnip, radish, and dandelion, or branched, as in most shrubs and trees. In the latter case the main axis is called the primary root, and the branches are secondary ones. 80. Fibrous and fascicled roots. - Where the main axis fails to develop, as in the corn and grasses generally, a number of independent branches take its place, forming what are known as fibrous roots. Both fibrous and tap- r°°ts maV be elther hard OI> fleshy- root of maple. The turnip and carrot are examples of fleshy taproots, the dahlia and rhubarb of fascicled roots. The function of both is the storage of nourishment. The sweet potato is an example of a tuberous root. 81. Practical importance of this distinction. -- The dif- ference between axial and fibrous roots has important bear- ings in agriculture. The first kind, which are characteristic of most dicot- yls, strike deep and draw their nour- ishment from the lower strata of the soil, while the fibrous and fascicled, or radial kinds, as we may call them for want of a -better name, spread out near the surface and are more dependent on external conditions. FIG. ST.— Fibrous root. 82. Roots that grow above ground. - - The kinds of roots that have just been considered are all subterranean, and bring the plant into relation with the earth, whether for the purpose of absorbing nourishment, or of mechanical sup- port, or, as in the majority of cases, for both. Many plants, THE ROOT 75 however, do not get their mineral nutrients directly from the soil, and these give rise to various forms suited to other conditions of alimentation. 83. Adventitious roots. — This name applies to any kinds of roots that occur on stems, or in other unusual positions. They may be considered as intermediate between the two classes named in 81; for while their starting point is above ground, they generally end by fixing themselves in the soil, where they often function as normal roots. Familiar examples are the roots that put out from the lower nodes of corn and sugar cane stalks, and serve both to supply additional mois- ture and to anchor the plant more firmly to the soil. Most plants will develop adventitious roots if covered with earth, or even if merely kept in contact with the ground. The gardener takes advantage of this capacity when he propa- gates by cuttings and layers. 84. Water roots. - - These are generally white and thread- like and more tender and succulent than ordinary soil roots, because they have less work to do. Floating and immersed plants, such as bladderwort and hornwort (Ceratophyllum) have no need of absorbent roots, since the greater part of their surface is in contact with water and can absorb directly what is needed. Land plants will often develop water roots and thrive for a time if the liquid holds in solution a sufficient quantity of air and. mineral nutrients. Place a cutting of wandering Jew in a glass of clear water, and in from four to six days it will develop beautiful water roots in which both hairs and cap are clearly visible to the naked eye. 85. Haustoria, from a Latin word meaning to drain, or exhaust, is a name given to the roots of parasitic plants, or such as live by attaching themselves to some other living organism, from which they draw their nourishment ready made. Their roots are adapted to penetrating the sub- stance of the host, as their victim is called, and absorbing the sap from it. Dodder and mistletoe are the best-known 76 PRACTICAL COURSE IN BOTANY FIG. 88. — Beech root: A, grown in unsterilized wood humus : p, strands of fungal hyphse, associated at a, with humus ; B, grown in wood humus freed from fungus by sterilization — it is not provided with fungal hyphae, and has root hairs, h. (A and B both several times magnified.) examples of plant parasites, though the latter is only partially parasitic, as it merely takes up the sap from the host and manufactures its own food by means of its green leaves. 86. Saprophytes. - - Akin to parasites are saprophytes, which live on dead and decay- ing vegetable matter. They are only partially parasitic and do not bear the haustoria of true parasites. Many of them, of which the Indian pipe (Monotropa) and coral root are familiar examples, obtain their nourishment in part, at least, by association with certain saprophytic fungi, which enmesh their roots in a growth of threadlike fibers that take the place of root hairs and absorb organic food from the rich humus in which these plants grow. Such growths are called mycorrhiza, meaning " fungal roots." Similar associations are formed by some of the higher plants also. The root- lets of the common beech and of certain of the pine family, for instance, are often enveloped in a network of fungus fi- bers, and in this case root hairs are developed very poorly, or not at all. Besides greatly increasing the absorbent surface by their ramification through the soil, the mycorrhizal threads may possibly benefit the plant in other ways also, as, FIG. 89. — An air plant (Tillandsia), growing on the underside of a bough. THE ROOT 77 for instance, by bringing about chemical changes that might aid in the work of nutrition. 87. Epiphytes, or air plants. — In the proper meaning of the word these are not parasitic, but use their host merely as a mechanical support to bring them into better light relations. The name, however, is loosely applied to all plants that find a lodgment on the trunks and branches of trees, whether parasites or true epiphytes that draw no nourishment from the host. Not in- frequently the latter is killed by them through suffocation, overweight- ing, or the constriction of the stems by close clinging twiners. 88. Aerial roots are such as have no connec- tion at all with the soil or with any host plant, ex- cept as they may lodge Upon the trunks and FlG- 90.— A single strand of Tillandsia ii . ,. usneoides, a rootless epiphyte belonging to the branches OI trees lOr a pineapple family ; better known as the " Span- support. In other than ish moss" that drapes the boughs ,ofAtree- so conspicuously in the warm parts of America. purely epiphytic plants, Two-thirds natural size. (Photographed by C, which get all their nour- R °'Keefe-> 78 PRACTICAL COURSE IN BOTANY ishment from the air, they are generally subsidiary to soil roots, like the long dangling cords that hang from some species of old grapevines ; or they subserve other purposes altogether than absorbing nourishment, as the climbing roots of the trumpet vine and poison ivy. A very remark- able development of aerial roots takes place in the " stran- gling fig " of Mexico and Florida, which begins life as a small epiphyte, from seeds dropped by birds on the boughs or trunks of trees. When it gets well started, the young plant sends down enormous aerial roots, which find their way to the ground, and in time so completely envelop the host that it is literally strangled to death (Plate 3, p. 73). When this support is removed, the sheathing roots take its place and become to all intents and purposes the stem of the fig tree, which now leads an independ- ent life. 89- The root system. — The entire mass of roots belonging to a plant, with all its rami- fications and subdivi- FIG. 91. — Root system of a tobacco plant. gionS, Composes a root system. The extent of root expansion is in general about equal to that of the crown, thus bringing the new and active parts under the drip of the boughs where the moisture is most abundant. Some plants have root systems out of all seeming proportion to their size. A catalpa seedling six months old showed, by actual measurement, 250 feet of root growth, and it is estimated that the roots of a thrifty cornstalk, if laid end to end, would extend a mile. In the development of the root system, a great deal depends upon external conditions. In a poor, dry soil, the roots have to travel farther in search of a livelihood, and so a larger system has to be developed than in a more favorable location. THE ROOT 79 Practical Questions 1. Which is better to succeed a crop of turnips on the same land, hay or carrots? (81.) 2. Write out what you think would be a good rotation for four or five successive crops based on the forms of the roots. 3. Study the following rotations and give your opinion about them, on the same principle. Suggest any improvements that may occur to you, and give a reason for the change. Beets, barley, clover, wheat; cotton, oats, peas, corn; oats, melons, turnips; cotton, oats, corn and peas mixed, melons ; cotton, hay, corn, peas. 4. Give three good reasons in favor of a rotation over a single-crop system. (24, 60, 62, 81.) 5. Which will require deeper tillage, a bed of carrots or one of straw- berries? (81.) 6. Explain why some plants keep green and fresh when the surface of the soil is dry, while others wilt or die. (81, 89.) 7. Which will better withstand drought, a crop of alfalfa or one of Indian corn? Why? (81.) 8. Which will interfere less with the trees if planted in an orchard, beets or onions ? (81.) 9. Ought a crop of hemp and tobacco to succeed each other on the same land? (81, 89.) 10. Why does a gardener manure a grass plot by scattering the ferti- lizer on the surface, while he digs around the roses and lilacs and 'deposits it under ground ? (81.) 11. Do the adventitious roots of such climbers as ivy and trumpet vine draw any nourishment from the objects to which they cling? (83-88.) 12. How can you tell ? 13. Do partial dependents of this kind injure trees by climbing upon them; and if so, how? (87,88.) 14. What is the use of the aerial roots of the scuppernong grape ? (88.) 15. Is the resurrection fern (Polypodium incanum), that grows on tree trunks in our Southern States, a parasite or an air plant? (87.) 16. On what plants in your neighborhood does mistletoe grow most abundantly ? Dodder ? 17. Is mistletoe injurious to the host? (85.) 18. Name some plants that are propagated mainly, or solely, by roots and cuttings. 19. Where do aerial roots get their nourishment? (88.) 20. Would they be of any use to a plant in a very cold or dry climate ? 21. Where should manure be placed to benefit a tree or shrub with wide-spreading roots? (66, 89.) 80 PRACTICAL COURSE IN BOTANY 22. Is it a wise practice to mulch a tree by raking up dead leaves and piling them around the base of the trunk, as is often done ? Why, or why not? (66,89.) Field Work (1) Examine the underground parts of hardy winter herbs in your neigh- borhood, also of any weeds or grasses that are particularly troublesome, and see if there is anything about the structure of these parts to account for their persistence. Note the difference between roots of the same species in low, moist places and in dry ones ; between those of the same kind of plants in different soils; in sheltered and in exposed situations. Study the direction and position of the roots of trees and shrubs with reference to any stream or body of water in the neighborhood. (The elm, fig, mulberry, and willow are good subjects for such observations.) Notice also whether there is any relation between the underground parts and the leaf systems of plants in reference to drainage and transpiration. (2) Observe the effect of root pull upon low herbs. Look along washes and gullies for roots doing the office of stems, and note any changes of structure consequent thereon. Study the relative length and strength of the root systems of different plants, with reference to their value as soil binders, or their hurtfulness in damaging the walls of cellars, wells, sewers, etc. Dig your trowel a few inches into the soil of any grov) or copse you happen to visit, note the inextricable tangle of roots, and consider the fierce competition for living room in the vegetable world that it implies. (3) Tests might be made of the different soils in the neighborhood of the schoolhouse by planting seeds of various kinds and noting the rate of germination ; first, without fertilizers, then by adding the different ele- ments in succession to see what is lacking. The field for study suggested by this subject is almost inexhaustible. CHAPTER IV. THE STEM I. FORMS AND GROWTH OF STEMS MATERIAL. — Vigorous young hop or bean seedlings grown in pots ; a fresh dandelion stalk ; a stem of pea, squash, cucumber, grape, or passion flower vine, with tendrils. APPLIANCES. — A bowl of fresh water ; rods of different sizes and smoothness for testing the hold of climbers. EXPERIMENT 54. To SHOW THE MOVEMENTS OF TWINING STEMS. — Raise a young hop or bean seedling in the schoolroom and allow it to grow about two decimeters — 8 to 10 inches — in length before providing it with a support. Does the stem form any coils? Bring it in contact with a suitable upright support and watch for a day or two. What happens ? Notice whether it starts to coil from right to left or from left ' to right and see if you can coax it to turn in the opposite direction. When it has reached the end of its stake, allow it to grow about five centimeters (two inches, approximately) beyond, and watch the revolution of the tip. Cut a hole through the center of a piece of cardboard about 14 centi- meters (five to six inches) in diameter, slip it over the loose end of the stem, and fasten it to the stake in a horizontal position, with a pin. Note the position of the stem tip at regular intervals and mark on the cardboard ; how long does it take to complete a revolution ? Does it continue to coil, or to coil as readily, after leaving its stake as before ? What would you infer from this as to the effect of contact in stimulating it to coil ? Find out by experiment if it can climb well by means of a glass or other smooth rod ; by a fine wire ; a broomstick ; a large, smooth post. See whether it does better on a horizontal or an upright support. EXPERIMENT 55. To ILLUSTRATE THE COILING OF STEMS. — Run a gathering thread in one side of a narrow strip of muslin and notice how the ruffle thus drawn will curl into a spiral when allowed to dangle from the needle. Can you think of any cause that might act on a stem in the same way ? Suppose, for instance, that one side should grow faster than the other ; what would be the effect ? (54.) Split the stem of a fresh dandelion, or other herbaceous scape, longi- tudinally, and immerse it in a pan of fresh water for a few minutes. Notice how the two halves curve outward, or even coil up like the strip of muslin. This is due to the tension caused by the more rapid absorption of the fti 82 PRACTICAL COURSE IN BOTANY thinner walled cells of the internal tissues. These, when relieved of the resistance of the thicker walled outer tissues, swell on their free side, but are held back on the other by the non-absorbent outer parts, as one side of the muslin ruffle was held by the gathering thread. EXPERIMENT 56. To FIND OUT WHETHER THE DIRECTION OF STEM GROWTH is INFLUENCED BY LIGHT. — Place two rapidly growing young pea, bean, sunflower, or squash plants, each with several well-developed leaves, in a room or box with a light exposure on one side only. After two or three days, notice the position of the stems in regard to the light. Does either one show a more decided inclination toward it than the other ? EXPERIMENT 57. Is THE LIGHT RELATION OF THE STEM INFLUENCED BY THE LEAVES? — Cut the leaves from one of the plants used in Exp. 56, covering the cut surfaces with vaseline to prevent "bleeding"; reverse the positions of both with regard to the light, and watch for two or three days. In which is the response to light the more rapid ? What does this indicate as one object of the stem in seeking light? What is the best position of a stem, ordinarily, for getting its leaves into the light ? 90. Classification. — Stems are classed according to (1) duration, as annuals, biennials, and perennials ; (2) with reference to hardness or softness of structure, as herbaceous and woody; (3) in regard to position and direction of growth, as erect, prostrate, climb- ing, inclined, declined, underground, etc. 91. Annuals complete their life cycle in a single season and then die down as soon as they have perfected their seed. Many of our most troublesome weeds be- long to this class and might be exterminated by the simple expedient of mowing them down before their time of flowering. FIG. 92. — Stems of red oak and hickory that have grafted themselves. THE STEM 83 92. Biennials, as the name implies, live for two years. Their energy during the first season is spent chiefly in laying by a store of nourishment, usually in the tissues of fleshy roots (70). By this means they get a good start in the second season and mature their seeds early. Many of our common gar- den vegetables, such as tur- nips, carrots, parsnips, and cabbage, belong to this class. Where is the nour- ishment stored in the cab- bage? 93. Perennials are plants that live on indefinitely, like most of our forest trees and woody-stemmed shrubs. shown in Fig- 237- Woody stems are usually perennial and may live for hun- dreds and even thousands of years, as those of the giant sequoias of California, and the famous chestnut of Mt. Etna. 94. Herbaceous stems are more or less succulent and die down after fruiting. They are usually annuals, though some kinds, like the garden geraniums and the common St.-John's- wort, show a tendency to become woody, especially at the base, and live on from year to year. Others, such as the hawkweed and dahlia, die down above ground in winter, but are enabled to keep their underground parts alive indefi- nitely, through the nourishment stored in them, and are thus perennial below ground and annual above. Woody- stemmed annuals, such as the cotton and castor oil plant, are not, properly speaking, herbs. In the tropical countries to which they belong they are perennial shrubs, or even small trees, but on being transplanted to colder regions FIG. 93. — A biennial plant, mullein, in winter condition with stem reduced to little more than a disk supporting a rosette of leaves. Notice how close they cling to the earth, and compare them with their fruiting condition a few months later as 84 PRACTICAL COURSE IN BOTANY have been compelled to take on the annual habit as an adaptation to climate. 95. Direction and habit of growth. — As to manner of growth, there are many forms, from the upright boles of FIG. 94. — Orange hawk- weed with runners. FIG. 95. — Prostrate stem of Lycopodium with assurgent branches. the beech and pine to the trailing, prostrate, and creeping stems of which we have examples in the running periwinkle, the prostrate spurge and the creeping partridge berry (Mitchella repens), respectively. Trailing and pros- trate stems are very apt to become creepers by the development of adventi- tious roots at their nodes wherever they come in contact with the soil. The root- ing stems of dewberries, the runners and stolons of strawberries and currants, are familiar examples. Between the extremes of prostrate and upright, stems may be inclined or bent in FIG. 90. — Diagram of stem growth : ps, surface of the ground ; various degrees. As shown in Fig. 96, e, erect position; d, ,-, -i f • i- ,• declined ; a, assurgent ; there are two modes of inclination : assur- gent, a, from the prostrate, p, toward the p, prostrate ; u, ver- tical direction under- ground. upright, e; and declined, d, from the upright THE STEM 85 toward the prostrate. Below the surface, ps, occur only underground stems. Is the prostrate habit an advantageous one for light exposure ? Can you think of any compensat- ing advantages a plant might derive from it ; for example, in regard to warmth and moisture ? 96. Climbing stems. - - These are such as lift themselves from the ground and attain the advantages of the upright position by clinging to supports of various kinds — usually, in a state of nature, the stems and boughs of other plants. The means of climb- ing may be : (1) by merely leaning upon or propping themselves up by the aid of the supporting object — ex- amples, the rose, wistaria, star jessa- mine (Jasminum offidnalis) ; (2) by coiling their main axes spirally around the support — hop, bean, morning-glory ; (3) by means of ad- ventitious roots — poison ivy, com- mon English ivy, trumpet vine (Tecoma radicans) ; (4) by organs specially developed for the purpose, called tendrils — gourd, cucumber, grape, pas- sion flower. 97. Tendrils. — The part assigned to do the work of climb- ing may be a secondary branch, a flower stem, a leafstalk, a leaf, a leaflet, or a group of leaflets (Fig. 98). Tendrils behave in general very much like twining stems, except that they are more sensitive and respond more quickly to any cause that may influence their movement. While young, their tips revolve just as do the tips of twining stems, until they meet with an object round which they can coil. When this happens, not only the part in contact with the object coils, but the free part between it and the main axis will usually respond by twisting itself into a helix (Fig. 99). As the distance between the base and tip of the tendril is shortened A B FIG. 97. — Twining stems : A, hop twining with the sun ; B, convolvulus twining against the sun. 86 PRACTICAL COURSE IN BOTANY by coiling, the body of the plant is drawn upward proportionally. It will be observed that the helix is interrupted at one or more points, above and below which the coils turn in opposite direc- tions. This is because the ten- dril is attached at both ends and cannot adjust itself to the oppo- site strains of torsion. Twist with your fingers a piece of tape so attached, and you will see that on one side of your hand it turns from right to left and on the other from left to right. FIG. 98. -Leaf of common pea, 98' The CaUSC °f twining. - showing upper leaflets reduced to Botanists are not fully agreed on this point. The explanation most generally accepted at present is that the twining of stems is due to the combined action of lateral and negative geotropism (51). The first ^^>s^ causes one side to grow more rapidly than the other, thus forming a succession of coils, while the second, by stimulating the upward growth of the axis, stretches it into a spiral, and in this way draws it more tightly round the support. For this reason twining stems do best on an upright support. In tendrils, the twining is thought to be due not to gravity, but to contact with a solid body, which, by inducing unequal de- velopment on opposite sides of the tendril, FIG. 99. — Stems . , ., ,, , . of a passion flower causes it to turn about an available object, transformed into Tne coiimg of the free part of the twining tendrils. (After ° GRAY.) organ is in response to the stimulus trans- THE STEM 87 mitted from the part in contact — stimulus, in this sense, denoting the influence of any external agent that calls forth a responsive adjustment on the part of the plant. 99. The object of the various habits of stem growth. - - To bring the growing parts of the plant into the best possible rela- tions with light and air is one of the special func- tions of the stem, and the various habits of growth described in this section have been developed with reference to this function. In the case of prostrate and underground stems other factors may intervene; can you name some of the causes that might influence the position of the stem in such cases? FIG. 100. — Showing the economy of labor and building material effected by the climbing habit. Notice how the grapevine coils like an anaconda around the tree boles, and overtops their tallest branches. Compare the diameter of the vine with that of the trees. Practical Questions 1. Why is the normal direction of most stems upright? (Exp. 56.) 2. Name a dozen woody-stemmed plants; a dozen with herbaceous stems. 3. Name all the plants you can think of that have prostrate stems, or leaf rosettes that hug the earth, like mullein and dandelion. Which of these are wintergreen plants ? Which are hot- weather growers ? 4. Can you explain in what ways both hot- weather and cold- weather plants may be advantaged by the habit of clinging close to the earth ? (94, 95.) 5. Is there any difference in the height of the stem of a dandelion flower and a dandelion ball ? 6. Of what advantage is this to the plant ? (Exp. 17.) 7. Name all the means you can think of by which a stem may climb, and give an example of each. 88 PRACTICAL COURSE IN BOTANY 8. Why do we support peas with brush, and hops or beans with poles ? (98; Exp. 54.) 9. Are the vines of gourds, watermelons, squashes, and pumpkins normally climbing or prostrate? How can you tell? (96, 97.) 10. Why does not the gardener provide them with poles or trellises to climb on? 11. Do twining plants grow equally well on horizontal and upright supports? (98; Exp. 54.) 12. If there is any difference, which do they seem to prefer ? 13. Can you give any reasons for thinking that the climbing habit might lead to parasitism? (83, 85, 87.) 14. What method of climbing would be most favorable to the develop- ment of such a habit ? (Suggestion : What mode of climbing brings the stem into closest contact with its support ?) 15. Name some plants the stems of which are used as food. 16. Name some from which gums and medicines are obtained. 17. Explain how it can benefit a plant to have its leaves, or some of them, modified into tendrils. (99.) 18. In what way is the loss of the normal function of the leaves so modi- fied, compensated for? (Exp. 57.) 19. Suppose the vine shown in Fig. 100 had to lift itself without the aid of a support ; could it reach the same height and carry the same weight of foliage and flowers with the same expenditure of labor and building material ? II. MODIFICATIONS OF THE STEM MATERIAL. — A shoot of asparagus ; thorny branches of locust, plum, or haw; a cactus plant; bulbs of lily and hyacinth or onion; tubers of potato ; rootstocks of iris, fern, or violet. If fresh specimens are not acces- sible, dried rootstocks of the sweet flag and Florentine iris may be obtained at the drug stores under the names of calamus and "orris" root. ioo. How to recognize modified parts. — Stems, like roots, are often modified to serve other than their normal purpose, and in adapting themselves to these new functions they sometimes undergo such changes of form and structure that it would be impossible to recognize their true nature from appearances alone. The safest tests in such cases are : (1) by a comparison of the parts of the modified struc- ture with those of known organs of the same kind ; and (2) by observing its position in reference to other parts. For THE STEM 89 instance, we know that the stem is the part of the plant which normally bears leaves and flowers, and if either of these, or if the small scales which often take the place of leaves, are found growing on any plant structure, we may usually take for granted that it is a stem. Then, again, as will be shown in the next chapter, buds and branches naturally appear only at the nodes, in or near the axil, or inner, angle made by a leaf with the stem. Hence, if you see any growth springing from such a position, you may generally conclude it to be a stem. 101. Stems as foliage. - The connection between stem and leaf is so intimate that we need not be surprised to find a frequent interchange of function between them, the leaf, or some part of it, doing the work of the stem (Fig. 98), the stem more often taking upon itself the office of the leaf. A common example is the garden aspar- agus. Examine one of the young shoots sold in the market, and notice that it bears a number of small scales in place of leaves. On an older shoot that has gone to seed, the green, threadlike appendages, which FIG. 101. — Stem-leaves are usually taken for foliage, will be (ciadophyiis) of a ruscus, bear- found to spring each from the axil insflowers- of one of these scales. What, therefore, are we to conclude that it is? In the butcher's-broom of Europe, the transformation has gone so far that the branches of the stem have assumed the flattened appearance of leaves (Fig. 101), but their real nature is evident both from their position in the axils of leaf scales, and from the fact that they bear flower clusters in the axil of a scale on their upper face. Another example of this sort of modification is seen in the pretty little myr- siphyllum of the greenhouses (wrongly called smilax), which 90 PRACTICAL COURSE IN BOTANY FIG. 102. — Thorn branches of Holocantha Emoryi, a plant growing in arid regions. is so much used for decoration. The delicate green blades are merely altered stems, shortened and flattened to simulate leaves. 1 02. Weapons of defense. - Conspicuous examples of these are the bristling thorns of the honey locust. Is their frequent branching any indication of their real nature ? Does it prove any- thing, or must you look for other evidence? What further indi- cations might you expect to find, if they are true branching stems? (100.) On old haw, plum, crab, and pear trees, stems can be found in all stages of transition, from stubby, ill-developed branches, to well- defined thorns. 103. Storage of nourishment. -- This is one of the most frequent causes of modifi- cation in both roots and stems. Of stems that grow above ground, the sugar cane probably comes first in economic importance on this account. In hot, arid regions, where the moisture drawn from the earth would, during prolonged drought, be too rapidly dissipated by an expanded surface of leaves, the whole plant, as in the case of the cactus, is sometimes compacted into a greatly thick- ened stem, which fills the triple office of leaf, stalk, and water reservoir. 104. The uses of underground stems. - It is in these that the storage of nourishment FIG. 103.— Melon most frequently takes place, and the modi- graecat\yS Condensed fications that stems undergo for this purpose stem for the stora^e . , . . , and preservation of are in some cases so great that their real moisture. THE STEM 91 FIO. 104. — Root- nature becomes apparent only after a careful examination. But while the chief function of underground stems is the storage of nourishment, they serve other purposes also. In plants requiring a great deal of moisture, like the ferns, and in others growing in dry places and needing to husband moisture carefully, like the blackberry lily, under- ground stems may be useful in preventing the too rapid evaporation that would take place through aerial stems. Defense against frost, cold, heat, and other dangers, as well as quickness of propagation, are also attained or assisted by this means. 105. Rootstocks and rhizomes. — From a prostrate stem like that shown in Fig. 95 to a creeping rootstock like the one in Fig. 104, the stock of creeping transition is so easy that we find no difficulty panic grass' in accounting for it. From the prostrate rootstock to the thickened storage rhizome (Fig. 105) of such plants as the iris, puccoon, bulrush, and Solomon's-seal, is a longer step, but the bud with its leaf scales at the growing tip, a, the remains of the flower stem at the node, 6, and the roots from the under surface sufficiently indicate its na- ture. The peculiar scars from which 0- the Solomon's seal takes its name are caused by the falling away each year of the flowering stem a, growing bud at of the season after its work is done, the tip ; b, remains of the past i • 11*1.11 i e j.i season's flower stem; c,c,c, scars leaving behind the node of the un- of old stems. (After GRAY.) derground stem from which it orig- inated. In this way the rhizome lives on indefinitely, growing and increasing at one end as fast as it dies at the other. Test a little of the substance of the rhizome with iodine. Of what does it consist? Of what use is it to the plant? 1 06. The tuber. — A still further thickening and shorten- c c 92 PRACTICAL COURSE IN BOTANY FIG. 106. -Potato tuber showing lenti- SCale ^present ? eels, A, A, or pores for air on the surface; the eye? (100.) S, leaf scale, or scar. ing of the rhizome gives rise to the tuber, of which the potato and the Jerusalem artichoke are familiar examples. Can you give any evidence to show that the potato is a modified stem? Find the point of attachment of the tuber to its stem and stand it on this end, which is its natural base. Notice that the eye sits in the axil of the little scale that forms the eyelid. What does the What is Do the scales occur in any regular order — that is, opposite, or alternating with, each other, like the leaves on a stem ? Look on the surface for a number of small, lens-shaped dots (A, A, Fig. 106) scattered irregularly over it. These are aerating pores called lenticels, and are found in most dicotyl stems. Does their presence help to throw light on the real nature of the tuber? If any sprouts occur on your specimen, where do they originate? Where do buds and sprouts originate on plants above ground ? Make a sketch of the outside of a potato, showing the lenticels, eyes, and scales, or the scars left by the scales in case they have fallen away, as has probably happened, if your specimen is an old one. Cut a small slice from the stem end of two notatoes. stand FIGS. 107, 108. — Transverse and longi- tudinal sections of the potato : A, skin ; B, cortical layer ; C, outer pith layer ; D, inner pith layer. THE STEM 93 them in coloring fluid for four or five hours, then divide into cross and vertical sections, as shown in Figs. 107, 108, and draw, labeling the parts that you can make out. Through which has the liquid ascended most rapidly? Test with iodine and find out in which part nourishment is most abun- dant. It is this abundant store of food that makes the potato such a valuable crop in cold countries like Norway and Iceland, where the seasons are too short to admit of the slow process of developing the plant from the seed. Compare a common potato with a sweet potato. Are there any eyes or buds on the latter ? Is there a scale below them? Do they occur in any regular order? Do you see any lenticels? The common potato and the sweet potato are both tubers ; can you give some of the reasons why the one is regarded as a modi- fied branch, and the other as a root? (100.) Com- pare their food contents ; which contains most starch? Which most sugar? How can you j udge about the sugar with- FlG- 109- — Scaly FIG. 1 10. — Scaly . bud of oak, enlarged. bulb of lily (GRAY). out a chemical test : 107. The bulb is a form of underground stem reduced to a single bud. Get the scaly bulb of a lily, and sketch it from the outside and in cross and vertical section. Compare it with the scaly winter buds of the oak and hickory, or other common deciduous tree. Make an enlarged sketch of the latter on the same scale as the lily bulb, and the resemblance will at once become apparent. The scales of the bulb are, in fact, only thick, fleshy leaves closely packed around a short axis that has become dilated into a flat disk. From the center of the disk, which is the terminal node of this transformed stem, rises the flower stalk, or scape, as it is called, of the season. After blossoming, the scape perishes with its bulb, and their place is taken by new ones which are developed 94 PRACTICAL COURSE IN BOTANY from the axils of the scales, thus revealing their leaflike nature. That bulbs are only modified buds is further shown by the bulblets that sometimes appear among the flowers of the onion, and in the leaf axils of certain lilies. They never develop into branches, but drop off and grow into new plants just as the subterranean bulbs do. The bulbs of the onion and hyacinth are still further modifications, in which the scales consist of the thickened bases of leafstalks that are dilated until each one completely of rnGonlon'di"videadf envelops the growing parts within. lengthwise, showing IO8. Morphology is the part of botany the base enlarged ., /. ,1 • • into the coat of a that treats ot the origin, form, and uses bulb- of the different organs of plants, and of the modifications they, undergo in adapting themselves to changes of condition or function. Organs or parts that have the same origin but have become adapted to dif- ferent functions, like the flattened stems of the butcher 's- broom or the bulb scales of the lily, are said to be homologous; those that are different in origin but adapted to the same function, as the sweet and common pota- toes, are analogous. In other words, homologous organs are morphologically alike, but may be physiologically dif- ferent ; analogous organs are alike physiologically, but differ morphologically. 109. Economic value of stems. - - We probably get a greater variety of economic products from the stem than from any other part of the plant. Consider the vast amount of food stored in underground stems like the potato ; the resins, gums, and sugar found in the sap of plants like the sugar cane, the pine, and India-rubber trees; the medicines, dyes, and extracts obtained from the tissues ; the valuable fibers, such as flax, jute, and hemp, furnished by the bast: the wood DU!D for making Dauer: and the timber THE STEM 95 for building and furnishing our houses that we get from the woody trunks of trees. When we think of all these things, it seems hardly possible to overestimate the importance of this part of the vegetable kingdom to man, or to exert ourselves too strenuously to regulate and prevent the de- struction of these invaluable natural resources. Practical Questions 1. Would you judge from the observations made in the foregoing sec- tion, that the work of an organ determines its form, or that the form deter- mines its work? (99, 100, 108.) 2. Which is the more important, form or function ? 3. Name some plants that are propagated by rootstocks ; by runners or stolons ; by rhizomes ; by tubers ; by bulbs. 4. What is the advantage of propagating in this way over planting the seed? (104,106.) 5. Mention any other advantages that the various plants named may gain from the development of their underground parts. (104.) 6. What makes the nut grass so troublesome to farmers in some parts of the country ? . 7. Is its "nut" a root or a tuber? How can you tell? (106.) 8. Suggest some ways for destroying weeds that are propagated in this way. 9. Could you get rid of wild onions in a pasture by mowing them down ? By digging them up ? (107.) 10. Is it wise for farmers to neglect the appearance of such a weed in their neighborhood, even though it does not infest their own land ? 11. Name any plants of your neighborhood, either wild or cultivated, that are valued for their rhizomes ; for their tubers. 12. What part of the plants named below do we use for food or other purposes? Ginger, angelica, ginseng, cassava, arrowroot, garlic, onion, sweet flag, iris, sweet potato, Cuba yam, artichoke. 13. Why are the true roots of bulbous and rhizome-bearing plants generally so much smaller in proportion to the other parts than those of ordinary plants ? (89,104.) 14. If the Canada thistle grows in your vicinity, examine the roots and see if there is anything about them that will help to account for its hardi- hood and persistency. 15. If you live in the region of the horse nettle (Solanum Carolinense), explain how it is helped by its root system. (89.) 96 PRACTICAL COURSE IN BOTANY III. STEM STRUCTURE A. MONOCOTYLS MATERIAL. — Fresh cornstalks with several well-developed nodes, some of which should have stood in coloring fluid from 1 to 3 hours. If fresh specimens cannot be obtained from the fields, a number of seedlings may be grown in boxes of rich earth and cared for by the pupils either at home or in the schoolroom ; they should be planted 4 or 5 weeks before needed. Asparagus and smilax sprouts may be used, or the stem of any large grass, or of wheat and other grains, but stalks of corn or sugar cane make the best subjects for study where they can be obtained. APPLIANCES. — A compound microscope will be needed for detailed study. Prepared slides can be used, but it is better for students to make their own sections where practicable. no. Gross anatomy of a monocotyl stem. — Obtain a fresh cornstalk, — preferably one that has begun to tassel, - and observe its external characters. How are the inter- p nodes divided from one another ? What ^ is the use of the very firm, smooth epider- mis ? Notice a hollow, grooved channel running down one side between the joints, or nodes ; does it occur in all of them ? FIG. 112.— Cross Is it on the same side or on the opposite r™ sides of alternate internodes? Follow one cuiar bundles ; c, cor- of these grooves to the node from which it originates ; what do you find there ? After studying the internal structure of the stalk, you will understand why this groove should occur on the side of an internode bearing a bud or fruit. Cut a cross section midway between two nodes, and ob- serve the composition of the interior ; of what does the bulk of it appear to consist? Notice the arrangement of the little dots, like the ends of cut-off threads, that are scattered through the pith ; where are they most abundant, toward the center or the circumference ? Make a vertical section through one of the nodes. Cut a thin slice of the pith, hold it up to the light, and examine THE STEM 97 with a hand lens. Observe that it is composed of a number of oblong cells packed together like bricks in a wall. These are filled with protoplasm and cell sap, and constitute what is known to botanists as the parenchyma or fundamental tissue from which all the other tissues are derived. Apply the iodine test ; in what parts does starch occur most abun- dantly? Draw out one of the woody threads run- ning through the pith. Break away a bit of the epidermis, and see how very closely they are packed on its inner surface. Trace the course of the veins in the bases of the leaves ; FlG 113 _ Ver_ find their point of union with the stem ; tical section of com- . ., , » ., , ,, , stalk (reduced) : g, with what part of it do they appear to be groove ; c, cortex • v, continuous? Has this anything to do with the greater abundance of fibers near the epi- chyma ; b, bud ; n, dermis ? Can you follow the fibers through the nodes, or do they become confused and intermixed with other threads there? (If a stalk of sugar cane can be obtained, the ring of scars left by the vascular bundles as they pass from the leaves into the stem will be seen beauti- fully marked just above the nodes.) If there is an eye or bud at the node, see if any of the threads go into it. Can you account now for the de- pression that occurs in the internode above the eye? Make drawings of both cross and vertical sections, showing the points brought out in your examination of the cornstalk. in. The vascular system. -- To find out the use of the threads that you have been tracing, examine a piece of a living stem that has stood in red ink for three to twenty-four hours. Notice the course the coloring fluid has taken ; what would you infer from this as to the use of the woody fibers ? These threads constitute what is called the vascular system of the stem, because they are made up of vessels or ducts, along which the sap is conveyed from the roots to the leaves PRACTICAL COURSE IN BOTANY and back from the leaves to the parts where it is needed after it has contributed to the elaboration of food. On account of this double line of communication which they have to maintain, the vascular threads, or bundles, as they are technically called, are double ; one part composed of larger vessels, carrying water up, the other consisting of smaller ones, bringing back the food. Can you give a reason for their difference in size ? 112. Woody monocotyls. -- Examine sections of yucca, smilax, or of palmetto from the handle of a fan, and compare them with your sketches of the cornstalk. In which are the vascular fibers most abun- dant? Which is the toughest and strongest? Why? Trace the course of the leaf fibers from the point of insertion to the interior. How does it differ from that of the fibers in a cornstalk? 113. Growth of monoco tyl stems . — After tracing the course of the leaf veins at the nodes of the cornstalk, you will have no difficulty in identifying these veins as part of the vascular system. In jointed stems like those of the corn and sugar cane and other grasses, their intercalation between the vas- cular bundles of the stem takes place, as we have seen, at the nodes, forming the hard rings known as joints; but in other mono- cotyls the fibers entering the stem from the leaves usually tend first downward, toward the interior (Fig. 114), then bend outward, toward the surface, where they become entwined with others and form the tough, inseparable cortex that gives to palmetto and bamboo stems their great strength. Generally, monocotyl stems do not increase in di- ameter after a certain point, and as they can contain only a limited number of vascular fibers, they are incapable of sup- nnrt.incr nn pvt.pnHprl svsfpm nf IPP.VPS rmrl FIG. 114. — Lon- gitudinal section through the stem of a palm, showing the curved course of the fibrovascular bundles (GRAY, after FALKENBERG). THE STEM 99 PLATE 4. — Forest of bamboo, showing the tall, straight, branchless habit of monocotyi stems. 100 PRACTICAL COURSE IN BOTANY plants of this class, with a few exceptions, like smilax and asparagus, are characterized by simple, columnar stems and a limited spread of leaves. Such plant forms are admirably adapted by their structure to the purposes of mechanical support. It is a well-known law of mechanics that a hollow cylinder is a great deal stronger than the same mass would be in solid form, as may easily be tested by the simple ex- periment of breaking in your fingers a cedar pencil and a , joint of cane or a stem of smilax of the same weight. In stems that may be technically classed as solid in structure, like the corn and palmetto, the interior is so light compared with the hard epidermis that the result is practically a hollow cylinder. 114. Minute study of a monocotyl stem. -- Place under the microscope a very thin transverse section of a cornstalk. The little dots that looked like the cut ends of threads to the naked eye will now appear as . 115. — Transverse section through^ the fibrovascular bundle of a cornstalk r^HFia^lliLr— Vertical section of the same ; a, annular tracheid ; sp, spiral tracheid ; a and a', rings of a decomposed annular m and m', ducts ; I, air space ; v, sieve tracheid ; v, sieve tubes ; s, companion tubes ; s, companion cells ; vg, strength- cells ; cp, bast ; I, air space ; vg, strength- ening fibers ; cp, bast ; /, /, parenchyma, ening tissue ; sp, spiral duct. the complex group of cells shown in Fig. 115. The same parts a.rp shown Inncnt.nrlirmllv in TTio- lift As sppn in nrnss spr»- THE STE&[ 101 tion, their arrangement suggests a grotesque resemblance to the face of an old woman wearing a pair of enormous specta- cles and surrounded by a cap frill of netting with very wide meshes. These are parenchyma cells, /, /, Fig. 115, and constitute the greater portion of the living tissues. The two large openings, m, mf , thaJwpresent the spectacles, are ducts for carrying water up tne stem. They are called pitted ducts on account of the bordered pits which cover their outer surface. The two smaller openings between and slightly below the pitted ducts are also vessels for carrying liquids up the stem. The lower one, a, is called the annular tracheid because its tube is strengthened by rings on the inside. The upper, smaller one, sp, is known as the spiral tracheid, because its walls are reinforced by spiral thickenings. Can you think what is the use of these strengthening contri- vances in the walls of conducting cells? (Suggestion: What is the use of the spiral wire on a garden hose?) The large, irregular opening below the ducts is an air space. What is its object? Why has it no surrounding wall? Next look above the ducts for a group of rhomboidal or hexagonal cells, v, v, with smaller ones, s, between them. The larger of these are sieve tubes, the smaller ones, companion cells. The sieve tubes carry sap down the stem after it has been made into food by the leaves. They get their name from the sievelike openings between the connecting walls of the cells which form them — as if a row of pepper boxes with perforations at both top and i -i i -i mi view ui nit; aievu tuuu bottom were placed end to end, so as to of a gourd stem, showing form a long tube divided into compart- Perforations- ments by perforated walls. Can you give a reason why the cells of ducts that carry elaborated nutriment should have a more open line of communication than those carrying crude sap ? [56 (2) .] Which one of the organic food substances was shown by Exp. 39 to be unable, or nearlv so, to pass through FIG. 117. — Horizon- tal view of the sieve tube 102 PRACTIQAP ;COURSE IN BOTANY u FIG. 118. — Side view of the sieve tube of a gourd stem : •pr, protoplasm layer ; u, albuminous con- tents, forming muci- laginous strand. the cell wall by osmosis? [56 (4).] The conducting cells are surrounded by a mass of strengthening fibers separating them from the parenchyma,/, and constituting with them a fibrovascular bundle. The larger vessels, m, m1 , a, and sp, compose the xylem, the harder, more woody part of the bundle, and the smaller ones, v, s, the phloem, or softer part. Notice also that there is no parenchyma in contact with the xylem and phloem in the fibro- vascular bundles of a monocotyl, to supply material for new growth, but they are entirely surrounded by a sheath of strength- ening tissue, whence such bundles are said to be closed) and are incapable of further growth by the addition of new cells. B. HERBACEOUS DICOTYLS MATERIAL. — Young stems of sunflower, hollyhock, burdock, ragweed, cocklebur, castor bean, or any large herbaceous plant. In schools un- provided with compound microscopes, the minute anatomy can be studied with some degree of profit by the aid of pictures. 115. Gross anatomy. — Examine the outside of a young stem of sunflower, burdock, or other herbaceous dicotyl. Notice whether it is smooth, or roughened with hairs, scales, ridges, or grooves. If hairy, observe the nature of the hairs, whether bristly, downy, sticky, etc. Notice the color of the epidermis, whether uniform, or splotched or striped with other colors, as, for example, jimson weed, and pigweed (amarantus). If there are any buds, branches, or flower stems, notice where they originate ; what is the angle be- tween the leaf and stem called? (100.) Make a transverse cut through a portion of the stem that has stood for a time in coloring fluid and examine with a lens. Four regions can easily be distinguished : (1) the epidermis, THE STEM 103 FIG. 119. — Transverse section of a very young stem of burdock, showing fibro- vascular bundles not completely united into a ring : e, epidermis ; c, primary cor- tex ; /, a ring of fibro vascular bundles ; p, central cylinder of parenchyma. e, Fig. 119; (2) the primary cortex, c; (3) a ring of fibro- vascular bundles, /; and (4) a central cylinder of paren- chyma, p. In some specimens there will be a fifth region, the pith, which will appear in the section as a white cir- cular spot in the center of the parenchyma. In specimens a little older ^| — C than the one shown in Fig. l£§J $|p — f 119, a narrow circular line- will be seen running through the ring of bundles nearly midway between their inner and outer extremities, con- necting them into an un- broken circle around the central cylinder. This is the cambium layer, which supplies the vascular region with materials for new growth, and thus enables dicotyl stems to increase in diameter by the successive addition of fresh vascular rings from year to year. Examine in the same way a vertical section, and find the parts corresponding to those shown in Fig. 119. Make en- larged sketches of both sections, labeling the various parts observed. 116. Minute structure of a dicotyl stem. — Place suc- cessively under a high power of the microscope thin trans- verse and longitudinal sections of the stem just examined, or such other specimen as the teacher may provide. Bring one of the fibrovascular bundles into the field, and try to make out the parts shown in Figs. 120 and 121. The corresponding parts in the two sections are indicated by the same letters. Notice the cortex, R, on the outside and the pith, M, on the inside ; between these, the cambium, C, the xylem, or woody tissue, included between the radiating lines X, and the newer tissues composing the phloem between the lines P. The 104 PRACTICAL COURSE IN BOTANY M C sb. b P 120 M R FIGS. 120-121. — Transverse and longitudinal sections of a fibrovascular bundle in the stem of a sunflower. The two sections are lettered to correspond : M , pith (parenchyma) ; X, xylem region ; P, phloem ; R, cortex ; s, spiral ducts ; sf, annular ducts t, t, pitted ducts ; C, cambium between the phloem and xylem regions ; sb, sieve tubes; b, bast ; e, bundle sheath; ic, cambium (parenchyma) cells ; k, wood fibers. THE STEM 105 cambium and pith, which includes the medullary rays so con- spicuous in perennial stems, are composed of live paren- chyma, cells, from which alone growth can take place ; they are the active part of the stem. The xylem contains the large vessels, t and s, that convey water up the stem, together with the wood fibers, h. These are the permanent tissues. After completing their growth the cells of the xylem gradu- ally lose their protoplasm, and all vitality ceases. Even the cell sap disappears, and sometimes the walls of the ducts are disintegrated, leaving a mere air space like that shown at I in Figs. 115 and 116. The dead cells and tissues, however, are by no means useless. They constitute the heartwood that is so valuable for timber, and serve an important purpose as a mechanical support for the stem. The phloem contains on its outer face a mass of hard fibers, b, called bast, and toward the interior, the sieve tubes, sb, with a number of smaller vessels that convey down the stem the sap containing the food made in the leaves. It is separated from the cortex by the bundle sheath, e, and on its other side, from the ex- terior face of the xylem by the cambium, C. In this position the growing cambium adds new cells to the inner side of the phloem, and to the outer side of the xylem, so that the former grows on its inner face and the latter on its outer. In peren- nial plants, as new rings are added to the xylem from season to season, the older ones die and are changed into heartwood, which thus gradually increases in thickness till in some of the giant redwoods and eucalypti, it may attain a diameter of thirty-five or forty feet. In the phloem, on the other hand, as new cells are added from within, the older ones are gradually changed into hard bast, 6, then into bark, and are finally sloughed off and fall to the ground. It is this free line of communication with the active cambium that enables dicotyl stems to grow on indefinitely, the sheath, e, being formed on the exterior face of the bundles only, leav- ing the other free, whence they are said to be open. Make drawings of cross and vertical sections of a dicotyl 106 PRACTICAL COURSE IN BOTANY FIG. 122. — Internal structure of a pine stem, showing longitudinal section of a fibrovascular bundle through a medullary ray, sm, sm' : s, tracheids ; t, bordered pits, surface view ; c, cambium ; v, sieve tubes ; vt, sieve pits, analogous to the sieve plates in dicotyl stems. stem as it appears under the microscope, labeling correctly all the parts observed. Show the shape and relative size of the different cells. Com- pare your drawings with those made in your study of monocotyl stems, and write in your notebook the essential points of difference between the two. 117. The stems of coni- fers, the group of Gymno- sperms to which the pine belongs, do not differ greatly from those of dicotyls, the chief difference being that the vascular bundles contain tracheids only, correspond- ing to the smaller vessels of FIG. 123. — Internal structure of a pine stem, showing transverse section of a tra- cheid : i, cell walls ; m, intermediate layer between walls of adjoining cells ; m', inter- cellular space here occupied by substance of intermediate layer; b, bordered pit in section at right angles to the surface; t, membrane for closing the pit canal. THE STEM 107 the phloem, s and s', shown in Fig. 121. These tracheids have large sunken places in their walls, called bordered pits (Fig. 123), closed by a very thin membrane through which water and dissolved food materials can more readily per- colate. In all other essentials, the internal structure of pine stems is like that of dicotyls. (See Plate 5.) C. WOODY STEMMED DICOTYLS MATERIAL. — Elm, basswood, mulberry, leathcrwood, and pawpaw show the bast well ; sassafras, slippery elm, and (in spring) hickory and willow show the cambium; grape and trumpet vine, the ducts. Some of the specimens used should be placed in coloring fluid from 3 to 8 hours before the lesson begins. The rate at which the liquid is absorbed varies with the kind of stem and the season. It is more rapid in spring and slower in winter. If a cutting stands too long in the fluid, the dye will gradually percolate through all parts of it ; care should be taken to guard against this. 118. The external layer. — While the primary structures, as shown in the last section, are essentially the same in all dicotyl stems, the continued yearly growth of perennials causes them to de- velop a number of secondary structures and variations of detail that differentiate them in a marked degree from soft- stemmed annuals. Take a piece of a three-year-old shoot of cherry, horse chestnut, or any convenient hardwood tree, and notice that the soft, green epidermis has given place to a thicker, harder, and usually darker colored bark. Notice the presence of lenticels (106) and their porous, corky texture for the ad- mission of air to the interior. They are slightly raised above the surface of the bark, and are usually round, or more or less elongated in different direc- tions, according as they are stretched vertically or hori- zontally by the growth of the axis. The characteristic mark- Fio. 124. — Part of a young China tree shoot, showing, A, lenticels; B, leaf scar ; C, C, traces left by the broken ends of fi brovascular bundles that passed from the stem in- to the leaf. Natural size. 108 PRACTICAL COURSE IN BOTANY PLATE 5. — Stem of a conifer, Sequoia gigantea, Mariposa Grove, California. The first branch, 6 feet in diameter, leaves the parent trunk 125 feet above the ground. The photographer sitting on one of the exposed roots affords a good standard for comparison. The tree is noted for its massive limbs. The smaller trees in the background show the characteristic mode of branching in trees of this class. THE STEM 109 ings of birch bark, which make it so ornamental, are due to the lenticels. In most trees they disappear on the older parts, where the bark is constantly breaking away and sloughing off. 119. Internal structures. — Cut a transverse section through your specimen, and notice under the epidermis a greenish layer of young bark ; beneath this a layer of rather tough, stringy bast fibers, and beyond these a harder woody substance that constitutes the bulk of the interior; within this, at the very center of the axis, we find a cylinder of lighter texture, the pith, or medulla, occupying the place of the soft parenchyma which fills this space in very young stems. Between the woody axis and the bark notice a more or less soft and juicy ring. 1 20. The cambium layer. — This is not always easily distinguishable with a hand lens, but is conspicuous in the stems of sassafras, slippery elm, and aristolochia. If some of these cannot be obtained, the presence of the cambium can be recognized by observing the tendency of most stems to " bleed," when cut, between the wood and bark. The reason for this is because the cambium is the active part of the stem, in which growth is taking place, and consequently it is most abundantly supplied with sap. In spring, es- pecially, it becomes so full of sap that if a rod of hickory or elder is pounded, the pulpy cambium is broken up and the bark may be slipped off whole from the wood. 121. Medullary rays. — Observe the whitish, silvery lines that radiate in every direction from the center, like the spokes of a wheel from the hub. These are the medullary rays, and consist of threads of pith that serve as lines of com- munication between the " central cylinder " and the grow- ing cambium layer. In old stems the central pith frequently disappears and its office is filled by the medullary rays, which become quite conspicuous. 122. Structural regions of a woody stem. — Sketch cross and vertical sections of your specimen, as seen under the lens, labeling the different parts. Refer to Figs. 125, 126, if you 110 PRACTICAL COURSE IN BOTANY have any difficulty in distinguishing the parts. In a year-old shoot (Fig. 125), the structural regions correspond closely to those shown in Fig. 119, except that the ring of fibro vascular bundles is here compact and woody, and crossed by the radiating lines of the medullary rays. In a three-year-old shoot (Fig. 126), the main divisions are the same, but the soft parenchyma of the central cylinder is replaced by the pith, and the vascular ring is composed of three layers corre- sponding to the three years of growth. In general, mature 171 125 126 FIGS. 125, 126. — Cross sections of twigs : 125, section across a young twig of box elder, showing the four stem regions : e, epidermis, represented by the heavy bounding line ; c, cortex ; w, vascular cylinder ; p, pith ; 126, section across a twig of box elder three years old, showing three annual growth rings, in the vascular cylinder. The radiating lines (ra), which cross the vascular region (w), represent the pith rays, the principal ones extending from the pith to the cortex (c). (From COULTER'S " Plant Relations.") dicotyl stems may be said to include four well-defined re- gions: (1) the epidermis, or the bark; (2) the cortex, made up of bast and certain other tissues; (3) the cambium; (4) the woody vascular cylinder, made up of concentric rings, each representing a year's growth. The pith, or me- dulla, constitutes a fifth region, but is obvious only in young stems. Notice the little pores or cavities that dot the woody part in the cross section; where are they largest and most abundant ? How are the rings marked off from one another ? THE STEM 111 These pores are the sections of ducts. They are very large in the grapevine, and a cutting two or three years old will show them distinctly. Examine sections of a twig that has stood in red ink from three to twelve hours, and observe the course the fluid has taken. How does this accord with the facts observed in your study of the conducting tissues in monocotyl and herbaceous stems? (Ill, 115, 116.) 123. The rings into which the woody cylinder is divided mark the yearly additions to the growth of the stem, which increases by the constant accession of new material to the outside of the permanent tissues (116). The cambium constantly advances outward, beginning every spring a new season's growth, and leaving behind the ring of ducts and woody fibers made the year before. As the work of the plant is most active and its growth most vigorous in spring, the largest ducts are formed then, the tissue becoming closer and finer as the season advances, thus causing the division into annual rings that is so characteristic of woody dicotyl stems. Each new stratum of growth is made up of the fibrovascular bundles that supply the leaves and buds and branches of the season. In this way we see that the increase of dicotyl trunks and branches is approximately in an elongated cone (Fig. 127), the number of rings gradually diminishing toward the top till at the terminal bud of each bough it is reduced to a single one, as in the stems of annuals. Sometimes a late autumn, succeeding a very dry summer, will cause trees to take on a second growth, and thus form two layers of wood in a single season. On this account we can- not always rely absolutely upon the number of rings in esti^ mating the age of a tree, though the method is sufficiently exact for all practical purposes. FIG. 127. — Dia- gram illustrating the annual growth of dicotyledons. 112 PRACTICAL COURSE IN BOTANY Practical Questions 1. Old Fort Moultrie near Charleston was built originally of palmetto logs; was this good engineering or not ? Why? (113.) 2. Explain the advantages of structure in a culm of wheat ; a stalk of corn; a reed. (113.) 3. Would the same quality be of advantage to an oak? Why, or why not? 4. Is it of any advantage to the farmer that grain straw is so light ? 5. Explain why boys can slip the bark from certain kinds of wood in spring to make whistles. (120.) 6. Why cannot they do this in autumn or winter? (123.) 7. Name some of the plants commonly used for this purpose. 8. Is the spring, after the buds begin to swell, a good time to prune fruit trees and hedges ? (120.) 9. What is the best time, and why ? 10. Why are grapevines liable to bleed to death if pruned too late in spring? (120, 123.) 11. Why are nurserymen, in grafting, so careful to make the cambium layer of the graft hit that of the stock? (120.) 12. In calculating the age of a tree or bough from the rings of annual growth, should we take a section from near the tip, or from the base ? Why? (123.) IV. THE WORK OF STEMS MATERIAL. — Leafy shoots of grape, balsam, peach, or other active young stems ; a cutting of willow, currant, or any kind of easily rooting stem. Two bottles of water ands some linseed or cottonseed oil. EXPERIMENT 58. Do THE LEAVES HAVE ANY ACTIVE PART IN EFFECTING THE MOVEMENT OF SAP IN THE STEM ? — Take two healthy young shoots of the same kind — grape, peach, corn, tropseolum, calla lily absorb rapidly. Trim the leaves from one shoot and close the cut surfaces with a little vase- line or gardener's wax to prevent loss of water by evaporation. Place the lower end of each in a glass jar or tumbler filled to the same height with water. Cut off under water a half inch from the bottom of each shoot, to get a fresh absorbing surface. This is necessary because exposure to air for even a second greatly hinders absorption by permitting the entrance of air into the severed ends of the ducts. Pour a little oil on the water in both jars to prevent evaporation. (Do not use kerosene ; it is injurious to plants.) At the end of twenty-four hours, which vessel has lost the more water ? How do you account for the difference ? THE STEM 113 EXPERIMENT 59. WHAT BECOMES OF THE WATER THAT GOES INTO THE LEAVES ? — Cover the top of the vessel containing the leafy twig used in the last experiment with a piece of card- board, having first cut a slit in one side, as shown in Fig. 128, so that it can be slid into place without injuring the stem. Invert over the twig a tumbler that has first been thoroughly dried, and leave in a warm, dry place. After an hour or two, what do you see on the inside of the tumbler ? Where did the moisture come from ? EXPERIMENT 60. THROUGH WHAT PART OF THE STEM DOES THE SAP FLOW UPWARD ? — Remove a ring of the cor- tical layer from a twig of any readily rooting dicotyl, such as willow, being careful to leave the woody part, with the cambium, intact. Place the end below the cut ring in water, as shown in Fig. 129. The leaves above the girdle will remain fresh. How is the water carried to them? How does this agree with the movement of red ink observed in 115 and 122? FIG. 128. — Experiment showing that moisture is thrown off by the leaves of plants. EXPERIMENT 61. THROUGH WHAT PART DOES THE SAP COME DOWN ? — Next prune away the leaves and protect the girdled surface with tin foil, or insert it twJF 'which had been below tne nec^ °f a ^eeP bottle to prevent evaporation, kept standing in and wait until roots develop. Do they come more water after the re- abundantly from above or below the decorticated moval of a ring of cortical tissue : a, level of the water ; ring? b, swelling formed at I24- The three principal functions of the the upper denuda- stem are i — (1) to serve as a mechanical sup- port and framework for binding the other organs together and bringing them into the best attainable relations with light and air ; (2) as a water carrier, or pipe line, for conveying the sap from the roots to the parts where it is needed ; and (3) as a receptacle for the storage of foods. 114 PRACTICAL COURSE IN BOTANY 125. Movement of water. — It has already been shown (71, 111) that a constant interchange of liquid is taking place through the stem, between the roots, where it is absorbed from the ground, and the leaves, where it is used partly in the man- ufacture of food. Just what causes the rise of sap in the stem is one of the problems of vegetable physiology that botanists have not yet been able to solve. There are, how- ever, certain forces at work in the plant, which, though they may not ac- count for all the phenom- ena of the movement, undoubtedly influence them to a great extent. From experiments 58- 61, we can obtain an idea of what some of these forces may be. 126. Direction of the current. — These experi- ments show that the up- ward movement of crude sap toward the leaves is mainly through the ducts in the woody portion of the stem, while the down- FIG. 130. — The stump of a large oak that was injured by lightning many years ago. The interior is completely decayed, leaving only a hollow shell of living tissue, from which branches continue to put forth leaves year after year. ward flow of elaborated sap from the leaves takes place chiefly through the soft bast and certain other vessels of the cortical layer. The action of the leaves in giving off part of the water absorbed, as shown in Exp. 59, probably has also an important influence on the course of sap movement. If loss of water takes place in any organ through growth or other cause, the osmotic flow of the thinner sap from the roots will set in that direction. THE STEM 115 127. Ringing fruit trees. - - The course of the sap explains why farmers sometimes hasten the ripening of fruit by the practice of ringing. As the food material cannot pass below the denuded ring, the parts above become gorged, and a pro- cess of forcing takes place. The practice, however, is not to be commended, except in rare cases, as it generally leads to the death of the ringed stem. The portion below the ring can receive no nourishment from above, and will gradually be so starved that it cannot even act as a carrier of crude sap to the leaves, and so the whole bough will perish. 128. Sap movement not circulation. — It must not be supposed that this flow of sap in plants is analogous to the circulation of the blood in animals, though frequently spoken of in pop- ular language as the " circulation of the sap." There is no central organ like the heart to regulate its flow, and the water taken up by the roots does not make a continual circuit of the plant body as the blood does of ours, but is dispersed by a process of general diffusion, partly into the air through the leaves and partly through the plant body as food, wherever it is needed. Figure 131 gives a good general idea of the movement of sap in trees, the arrows indicating the direction of the movement of the different substances. 129. Unexplained phenomena. — Though the forces named above undoubtedly exert a powerful influence over sap movement, their combined action has not been proved capable of lifting the current to a height of more than 200 feet, while in the giant redwoods of California and the tower- ing blue gums of Australia, it is known to reach a height of more than 400 feet. The active force exerted by the cell protoplasm has been suggested as an efficient cause, but as FIG. 131. — Diagram show- ing general movement of sap. 116 PRACTICAL COURSE IN BOTANY the upward flow takes place through the cells of the xylem, which contain no protoplasm (116), this explanation is in- adequate, and we must be content, in the present state of our knowledge, to accept the fact as one which science has yet to account for. Practical Questions 1. Why will a leafy shoot heal more quickly than a bare one ? (125, 126; Exp. 58.) 2. Why does a transverse cut heal more slowly than a vertical one ? (126, 127.) 3. Why does a ragged cut heal less rapidly than a smooth one? 4. Why does the formation of wood proceed more rapidly as the amount of water given off by the leaves is increased ? (126; Exp. 59.) 5. Why do nurserymen sometimes split the cortex of young trees in summer to promote the formation of wood ? (116, 118.) 6. What is the advantage of scraping the stems of trees ? 7. Explain the frothy exudation that often appears at the cut ends of firewood, and the singing noise that accompanies it. [120, 124 (2).] 8. Of what advantage is it to high climbing plants, like grape and trumpet vine (Tecoma), to have such large ducts? (Ill, 116, 122.) 9. Why is the process of layering more apt to be successful if the shoot is bent or twisted at the point where it is desired to make it root ? (127; Exps. 60, 61.) 10. Why do oranges become dry and spongy if allowed to hang on the tree too long ? (72, 126; Exps. 60, 61.) 11. Why will corn and fodder be richer in nourishment if, at harvest, the whole stalk is cut down and both fodder and grain are allowed to mature upon it? (126, 127; Exps. 60, 61.) 12. Why should we protect the south side rather than the north side of tree trunks in winter ? (33.) 13. Why in pruning a branch is it best to make the cut just above a bud? (Exps. 60, 61.) 14. Why is the rim of new bark, or callus, that forms on the upper side of a horizontal wound, thicker than that on the lower side? (126, 127; Exps. 60, 61.) 15. Why is it that the medicinal or other special properties of plants are found mostly in the leaves and bark, or in the parts immediately under the bark ? (120, 126.) 16. Why does twisting the footstalk of a bunch of grapes, just before ripening, make them sweeter ? (127.) THE STEM 117 PLATE 6. — A white oak, one of the monarchs of the dicotyl type. The owner of the ground on which this noble tree stands left a clause in his will bequeathing it in perpetuity a territory of 8 feet in every direction from its base. Refer to 89 and decide whether such an amount of standing room is sufficient to secure the preser- vation of this beautiful object. 118 PRACTICAL COURSE IN BOTANY 17. Is it a mere superstition to drive nails into the stems of plum and peach trees to make them bear larger or more abundant fruit ? (126, 127.) 18. Why is a living corn stalk heavier than a dry one ? (124.) 19. Why is a stalk of sugar cane heavier than one of corn ? Suggestion : Which is the heavier, pure water, or water holding solids in solution ? V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES MATERIAL. — Select from the billets of wood cut for the fire, sticks of various kinds ; hickory, ash, oak, chestnut, maple, walnut, cherry, pine, cedar, tulip tree, all make good specimens. Red oak shows the medullary rays well. Get sticks of green wood, if possible, and have them planed smooth at the ends. Collect also, where they can be obtained, waste bits of dressed lumber from a carpenter or joiner. If nothing better is avail- able, any pieces of unpainted woodwork about the schoolroom will furnish subjects for study. 130. Detailed structure of a woody stem. — Select a good-sized billet of hard wood, and count the rings of annual growth. How old was the tree or the bough from which it was taken? Was its growth uniform from year to year? How do you know? Are the rings broader, as a general thing, toward the center or the circumference? How do you account for this ? Is each separate ring of uniform thickness all the way round? Mention some of the cir- cumstances that might cause a tree to grow less on one side than on the other. Are the rings of the same thickness in all kinds of wood ? Which are the more rapid growers, those with broad or with narrow rings? Do you notice any dif- ference in the texture of the wood in rapid and in slow grow- ing trees? Which makes the better timber as a general thing, and why ? 131. Heartwood and sapwood. — Notice that in some of your older specimens (cedar, black walnut, barberry, black locust, chestnut, oak, Osage orange, show the differ- ence distinctly) the central part is different in color and text- ure from the rest. This is because the sap gradually abandons the center (116, 123) to feed the outer layers, where growth in dicotyls takes place; hence, the outer part of the stem THE STEM 119 FIG. 132. — Cross section through a black oak, showing heart- wood and sapwood. (From PINCHOT, U. S. Dept. of Agr.) FIG. 133. — Vertical section through a black oak. U. S. Dept. of Agr.) (From PINCHOT, 120 PRACTICAL COURSE IN BOTANY usually consists of sapwood, which is soft and worthless as timber, while the dead interior forms the durable heart- wood so prized by lumbermen. The heartwood is useful to the plant principally in giving strength and firmness to the axis. It will now be seen why girdling a stem, — that is, chip- ping off a ring of the softer parts all round, will kill it, while vigorous and healthy trees are often seen with the center of the trunk entirely hollow. 132. Different ways of cutting. — In studying the vertical arrangement of stems, two sections are necessary, a radial and a tangential one. The former passes along the axis, splitting the stem into halves (Fig. 135) ; the latter cuts between the axis and the perimeter, split- ting off a segment from one side (Fig. 136). The appear- ance of the wood used in car- pentry and joiner's work is due largely to the manner in which the planks are cut. 133. The cross cut. — The section seen at the end of a log (Figs. 132, 134) is called by carpenters a cross cut. It passes at right angles to the grain of the wood, and severs what important structures? (116, 119, 122.) Examine a cross cut at the end of a rough plank, or the top of a stump or an old fence post, and tell why this kind of cut is seldom used in carpentry. 134. The tangent ^ cut is so called be- cause it is made at '^^-7an^^ right angles to the ing ends of the medullary rays. 134 135 136 FIGS. 134-136. — Diagrams of sec- tions of timber: 134, cross section ; 135, radial; 136, tangential. (From PINCHOT, U. S. Dept. of Agr.) THE STEM 121 radius of a log. Repeat the geo- metrical principle upon which such a cut is described as " tangential." It passes through the medullary rays and the annual rings diagonally (Fig. 136), and is the cheapest way of cutting timber, since the entire log is made into planks and there is no waste except the " slabs " and " edgings," as shown in Fig. 138. The cut ends of the medullary rays appear on the surface as small lines or slits (Fig. 137), and give to this kind of plank its peculiar grain- ing. The wavy or " watered " appearance of the annual rings (Figs. 133, 136, 140, 141), so often rrr * trrr FIG. 138. — Diagram to show the common method of sawing a log. The circles represent rings of annual growth : R, R, diam- eter of the log ; r, r, r and t, t, t, boards cut perpendicular to it, giving for the two or three cen- tral ones radial, for the others, tangential, cuts. The waste por- tions are the " slabs " and " edg- ings," shown in the dark seg- ments at R, R, and the small triangular blocks, e, e, e. seen in cheap furniture and in the woodwork of cheaply constructed houses, is caused by the tangential cut, which strikes them at various angles. 135. The radial, or quartered cut, familiar to most of us in the " quar- tered oak " of commerce, passes through the center of the log and cuts the rings of annual growth per- pendicularly, giving it the " striped" appearance (Fig. 135) seen in the best woodwork. It gets its name from the practice of dealers in first sawing a log into quarters and then cutting parallel to the radius pass- ing through the middle of each quarter, as shown in Fig. 139. In this way each cut strikes the rings FIG. 139. — Diagram illustrat- ing the "quartered " cut : d, d and d' d', radial cuts (diameters) by which the log is " quartered " ; c, center of the log ; r, r, radii passing through the middle of each quarter, parallel to which the plants t, t, t BIG cut, The perpendicularly, but except in the circles represent rings of annual growth. case of very large logs, only narrow 122 PRACTICAL COURSE IN BOTANY planks can be obtained in this manner. A better way of treating small logs is shown in Fig. 138, where the three central planks, r,r,r, on and near the diameter, will give the " quartered " effect, while the rest can be used for the cheaper tangential cuttings. Examine a piece of quartered board, or a log of wood that has been split down the center, and notice FIG. 140. — Sections of sycamore wood : a, tangential ; b, radial ; c, cross. (From PINCHOT, U. S. Dept. of Agr.) FIG. 141. — Section of white pine wood. (From PINCHOT, U. S. Dept. of Agr.) that the medullary rays appear as silvery bands or plates (Figs. 140, 141). This is because the cut runs parallel to them. It is the medullary rays chiefly that give to commer- cial woods their characteristic graining. Knots, buds, and other adventitious causes also influence it in various degrees. 136. The swelling and shrinking of timber. — The ca- pacity possessed by certain substances of bringing about an THE STEM 123 FIG. 142. — Section of tree trunk showing knot. 144 increase of volume by the absorption of liquids is termed imbibition. Care must be taken not to confound imbibi- tion with capillarity. (Exp. 53.) When liquids are carried into a body by capillary attraction, they merely fill up vacant spaces already exist- ing between small particles of the substance, and therefore do not cause any swelling or increase in size. When imbibition takes place, the molecules, or chemical units of the liquid, force their way between those of the imbibing substance, and thus, in making room for themselves, bring about an in- crease in volume of the imbibing body. To this cause is due the alternate swelling and shrinking of timber in wet and dry weather. 137. Knots. — Look for a billet with a knot in it. Notice how the rings of growth are disturbed and displaced in its neighborhood. If the knot is a large one, it will itself have rings of growth. Count them, and tell what its age was when it ceased to grow. Notice where it originates. Count the rings from its point of origin to the center of the stem. How old was the tree when the knot began to form? Count the rings from the origin of the knot to the circumference of the stem ; how many years has the tree lived since the knot was formed ? Does this agree with the age of the knot as deduced from its own rings? As the tree may continue to live and grow indefinitely after the bough which formed the knot died or was cut away, there will probably be no corre- spondence between the two sets of rings, especially in the case of old knots that have been covered up and embedded in FIGS. 143-144. — Dia- grams of tree trunks, show- ing knots of different ages : 143, from tree grown in the open ; 144, from tree grown in a dense forest. 124 PRACTICAL COURSE IN BOTANY the wood. The longer a dead branch remains on a tree the more rings of growth will form around it before covering it up, and the greater will be the disturbance caused by it. Hence, timber trees should be pruned while very young, and the parts removed should be cut as close as possible to the main branch or trunk. Sometimes knots injure lumber very much by falling out and leaving the holes that are often seen in pine boards. In other cases, however, when the knots are very small, the irregular markings caused by them add greatly to the beauty of the wood. The peculiar marking of bird's- eye maple is caused by abortive buds buried in the wood. Practical Questions 1. Is the swelling of wood a physical or a physiological process? 2. Does wood swell equally with the grain and across it ? (Suggestion: test by keeping a block under water for 10 to 20 days, measuring its dimen- sions before and after immersion.) 3. In building a fence, what is the use of "capping" the posts ? (133.) 4. In laying shingles, why are they made to touch, if the work is done in wet weather, and placed somewhat apart, if in dry weather? (136.) 5. What is the difference between timber and lumber? Between a plank and a board ? Between a log, stick, block, and billet ? 6. Why does sap wood decay more quickly than heartwood? (131.) 7. Explain the difference between osmosis, diffusion, capillarity, and imbibition. (9, 56, 57, 136; Exp. 53.) VI. FORESTRY 138. Practical bearings. -- This part of our subject is closely related to lumbering and forestry. The business of the lumberman is to manufacture growing trees into mer- chantable timber, and to do this successfully he must under- stand enough about the structure of wood to cut his boards to the best advantage, both for economy and for bringing out the grain so as to produce the most desirable effects for ornamental purposes. 139. Forestry has for its object: (1) the preservation and cultivation of existing forests ; (2) the planting of new THE STEM 125 PLATE 7. — Timber tree spoiled by standing too much alone in early youth. Notice how the crowded young timber in the background is righting itself, the lower branches dying off early from overshading, leaving tall, straight, clean boles. (From PINCHOT, U. S. Dept. of Agr.) 126 PRACTICAL COURSE IN BOTANY ones, or the reforestation of tracts from which the timber has been destroyed. Forests may be either pure, that is, com- posed mainly of one FIG. 145. — After the forest fire. kind of tree, as a pine or a fir wood ; or mixed, being made up of a vari- ety of different growths, as are most of our com- mon hardwood forests. 140. Enemies of the forest. — The first step in the preservation of our forests is to know the dangers to be guarded against. The chief of these are : (1) fires; (2) the igno- rance or recklessness of man in cutting for commercial purposes ; (3) fungi; (4) injurious insects; (5) sheep, hogs, and other animals that eat the seeds and the young, tender growth. 141. How to protect the forests. — The annual de- struction of forests by fires probably exceeds that from all other causes combined. The only effectual safeguard against this danger is watch- fulness on the part of every- body. We can each one of us help in this work by at least being careful ourselves never to kindle a fire in the woods without taking every precaution against its FIG. 146. — Oyster fungus on linden. THE STEM 127 spreading. A single match, or the glowing stump of a cigar, carelessly thrown among dry leaves or grass, may start a conflagration that will destroy millions of dollars' worth of standing timber. To prevent the spread of fungi, dead trees should be re- moved, and broken or decayed branches trimmed off and the cut surfaces painted. Birds which destroy insects should be protected ; sheep and hogs should be kept out, and dead leaves left on the ground to cover the roots and fertilize the soil with the humus created by their decay. Finally, none but mature trees should be cut for industrial purposes, and the cutting ought to be done in such a way that the young surrounding growth will not be injured by the falling trunks. 142. The usefulness of forests. — Aside from the value of their products, forests are useful in many other ways. They influence climate beneficially by acting as windbreaks, by giving off moisture (Exp. 58), by shading the soil, and thus preventing too rapid evaporation. Their roots also help to retain the water in the soil, and by this means tend to prevent the washing of the land by heavy rains and to restrain the violence of freshets. 143. Forests and water supply. — It is especially im- portant that the watershed of any region should be well protected by forests, to prevent contamination of the streams and to insure an unfailing supply of water by checking the escape of the rainfall from the soil. Practical Questions 1. Explain the difference between a forest, grove, copse, wood, wood- land. 2. In pruning a tree why ought the branch to be cut as close to the stock as possible? (137.) 3. Name the principal timber trees of your neighborhood. What gives to each its special value ? 4. Name six trees that produce timber valuable for ornament; for toughness and strength. 128 PRACTICAL COURSE IN BOTANY 5. Which is the better for timber, a tree grown in the open, or one grown in a forest, and why? (Plate 7.) 6. What are the objects to be attained in pruning timber trees? Or- chard and ornamental trees ? 7. Is the outer bark of any use to a tree, and if so, what ? 8. Why should pruning not be done in wet weather? [140 (3), 141.] 9. Why should vertical shoots be cut off obliquely? [133, 140 (3), 141.] Field Work (1) Make a study of the various climbing plants of your neighborhood with reference to their modes of ascent, and the effect, injurious, or other, upon the plants to which they attach themselves. Note the origin and position of tendrils, and try to make out what modification has taken place in each case. Consider the twining habit in reference to parasitism, especially in the case of soft-stemmed twiners when brought into contact with soft-stemmed annuals. Observe the various habits of stem growth: prostrate, declined, ascending, etc., and decide what adaptation to cir- cumstances may have influenced each case. (2) Notice the shape of the different stems met with, and learn to recognize the forms peculiar to certain of the great families. Observe the various appliances for defense and protection with which they are provided, and try to find out the meaning of the numerous grooves, ridges, hairs, prickles, and secretions that are found on stems. Always be on the alert for modifications, and learn to recognize a stem under any disguise, whether thorn, tendril, foliage, water holder, rootstock, or tuber. (3) Note the color and texture of the bark of the different trees you see and learn to distinguish the most important kinds : (a) scaly — peeling off annually in large plates, as sycamore, shagbark- hickory ; (6) fibrous — detached in stiff threads and fibers, as grape ; (c) fissured — split into large, irregular cracks by the growth of the stem in thickness, as oak, chestnut, and most of our large forest trees ; (d) membranous — separating in dry films and ribbons, as common birch (Betula alba). Observe the difference in texture and appearance of the bark on old and young boughs of the same species. Try to account for the varying thickness of the bark on different trees and on different parts of the same tree. Notice the difference in the timber of the same species when grown in different soils, at different ages of the tree, and in healthy and weakly specimens. Find examples of self-pruning trees (Plate 7), and explain how the pruning was brought about, THE STEM 120 (4) Select a small plot, about a fourth of an acre, of any wooded tract in your neighborhood, and make a study of all the trees and shrubs it con- tains. Make a list of the different kinds, with the number of each. Take note of those that show themselves, by vigor and abundance of growth, best adapted to the situation. These are the "climax" or dominant vegetation of the plot. Find out, if you can, to what cause their superi- rity is due. 130 PRACTICAL COURSE IN BOTANY CHAPTER V. BUDS AND BRANCHES I. MODES OF BRANCHING MATERIAL. — For determinate growth, have twigs of an alternate and an opposite-leaved plant showing well-developed terminal buds: hickory, sweet gum, cottonwood, poplar, chestnut, are good examples of the first ; maple, ash, horse-chestnut, viburnum, of the second ; for the two- forked kind, mistletoe, buckeye, horse-chestnut, jimson weed, lilac. For showing indefinite growth : rose, willow, sumach, and ailanthus are good examples. Gummy buds, like horse-chestnut and poplar, should be soaked in warm water before dissecting, to soften the gum ; the same treatment may be applied when the scales are too brittle to be handled without breaking. Buds with heavy fur on the scales cannot very well be studied in section; the parts must be taken out and examined separately. 144. Modes of branching. — Compare the arrangement of the boughs on a pine, cedar, magnolia, etc., with those of the elm, maple, apple, or any of our common deciduous trees. Draw a diagram of each, showing the two modes of growth. The first represents the excurrent kind, from the Latin excurrere, to run out ; the second, in which the trunk seems to di- vide at a certain point and flow away, losing itself in the branches, called deliquescent. IS FIG. 147. — Dia- T . , ,. gram of excurrent from the Latin deliques- FIG. 148. — Diagram of deliquescent growth. cere, to melt or flow away. The great majority of stems, as a little observation will show, present a combination of the two modes. 131 132 PRACTICAL COURSE IN BOTANY 145- Terminal and axillary buds. — Notice the large bud at the end of a twig of hickory, sweet gum, beech, cotton- wood, etc. This is called the terminal bud because it ter- minates its branch. Notice the scars left by the leaves of the season as they fell away, and look for small buds just above them. These are lateral, or axillary, buds, so called because they spring from the axils of the leaves. How many leaves did your twig bear? What difference in size do you notice between the terminal and lateral buds? 146. The leaf scars. — Examine the leaf scars with a hand lens, and observe the number and position of the little dots in them. Ailanthus, varnish tree, sumach, tr and China tree show these very distinctly. tr They are called leaf traces, and mark the points where the fibrovascular bundles from the leaf veins passed into the stem. FIG. 149. — winter Look on the bark, or epidermis, for lenticels. twig of sugar maple : t, terminal bud ; ax, axillary buds ; Is, leaf scars ; tr, leaf traces ; I, lenticels ; rs, ring of scars left by bud scales of preceding season. 147. Bud scales and scars. — Notice the , hard scales by which the winter buds are covered in most of our hardy trees and shrubs. Remove these from the terminal one of your specimen, and notice the ring of scars left around the base. Look lower down on your twig for a ring of similar scars left from last year's bud. Is there any difference in the appearance of the bark above and below this ring ? If so, what is it, and how do you ac- count for it ? Is there more than one of these rings of scars on your twig, and if so, how many ? How old is the twig and how much did it grow each year ? Has its growth been uniform, or did it grow more in some years than in others ? 148. Arrangement and use of the scales. — Notice the manner in which the scales overlap so as to " break joints," like shingles on the roof of a house. Where the leaves are opposite, the manner of superposition is very simple. Re- BUDS AND BRANCHES 133 --5 -5 FIG. 150. — Dia- gram of opposite bud scales. move the scales one by one, representing the number and position of the pairs by a diagram after the model given hi Fig. 150. In the bud of an alternately branched twig the order will be different, and the diagram must be varied ac- cordingly. Do you observe any difference as to size and texture between the outer and inner scales? Notice how the former inclose the tenderer parts within like a protecting wall. In cold climates the outer scales are frequently coated with gum, as in the horse-chestnut, for greater security against the weather. The hickory and various other trees have the inner scales covered with fur or down that envelops the tender bud like a warm blanket. 149. Nature of the scales. - - The posi- tion of the scales shows that they occupy the place of leaves or of some part of a leaf. In expanding buds of the lilac and many other plants, they can be found in all stages of transition, from scales to true leaves. In the buckeye and horse- chestnut, they will easily be recognized as modified leaf stalks (Fig. 151). In the tulip tree, magnolia, India rubber tree, fig, elm, and many others, they represent appendages called stipules, often found at the bases of leaves. (See 165, 166.) In this case a pah- of scales is attached with each separate leaflet, and as the growing axis lengthens in spring, they are carried apart by the elongation of the inter- nodes so that the scars are separated, a pair at each node, making rings all along the stem, as shown in Fig. 152, in- stead of having them compacted into bands at the base of FIG. 151.— Devel- opment of the parts of the bud in the buckeye. (After GRAY.) 134 PRACTICAL COURSE IN BOTANY FIG. 152. — Stem of tulip tree : the bud. These scars are sometimes very persistent, and in the common fig and magnolia may often be traced on stems six to eight years old. Do they furnish any indication as to the relative age of the different parts of the stem, like the bands of scars on twigs of horse-chestnut and hickory ? Give a reason for your answer. (Fig. 152.) 150. Different rates of growth. — Notice the very great difference between branches in this respect. Sometimes the main stem will have lengthened from twenty to fifty centimeters or more in a single season, while some of the lateral ones will have grown but an inch or two in four or five seasons. One reason for this is because the terminal bud, being on the great trunk line of sap scars left by stipular scales ; i, i, leaf scars, movement, gets a larger share 01 nourish- ment than the others, and being stronger and better developed to begin with, starts out in life with better chances of success. Make a drawing of your specimen, showing all the points brought out in the examination just made. Cut sections above and below a set of bud scars and count the rings of annual growth in each section. What is the age of each? How does this agree with your calculation from the number of scar clusters left by the bud scales ? 151. Irregularities. — Take a larger bough of the same kind that you have been studying, and observe whether the arrangement of branches on it corresponds with the arrange- nient of buds on the twig. Did all the buds develop into branches? Do those that did develop all correspond in size and vigor? If all the buds developed, how many branches would a tree produce every year? In the elm, linden, beech, hornbeam, hazelnut, willow, and various other plants, the terminal bud always dies and the one next in order takes its place, giving rise to the more or BUDS AND BRANCHES 135 Fio. 153. — Bud development of beech : a, as it is, many buds failing to develop ; b, as it would be if all the buds were to live. less zigzag axis that generally characterizes trees of these species. (Fig. 153.) 152. Forked stems. -- Take a twig of buckeye, horse- chestnut, or lilac, and make a care- ful sketch of it, showing all the points that were brought out in the examination of your previous speci- men. Which is the larger, the lat- eral or the terminal bud ? Is their arrangement alternate or opposite ? What was the leaf arrangement? Count the leaf traces in the scars ; are they the same in all ? If all the buds had developed into branches, how many would spring from a node ? Look for the rings of scars left by the last season's bud scales. Do you find any twig of more than one year's growth, as measured by the scar rings? Look down between the forks of a branched stem for a round scar. This is not a leaf scar, as we can see by its shape, but one left by the last season's flower cluster. The flower, as we know, dies after perfecting its fruit, and so a flower bud cannot continue the growth of its axis as other buds do, but has just the op- posite effect and stops all further growth in that direction. Hence, stems and branches that end in a flower bud cannot continue to develop their main axis, but their growth is usually carried on, in alternate-leaved stems, by the nearest lateral bud, or in opposite-leaved ones, by the nearest pah* of buds. In the first case there results the zigzag spray characteristic of such trees as the beech and elm (Fig. 155, B) ; in the second, the two-forked, or dickotomous branching, FIG. 154. — Two- forked twig of horse- chestnut. 136 PRACTICAL COURSE IN BOTANY FIG. 155. — Dia- grams of two-forked branching. The pointed bodies in the forks shows where ter- minal flower buds or flower clusters have exemplified by the buckeye, horse-chestnut, jimson weed, mistletoe, and dogwood (Fig. 155, A). Draw a diagram of the buckeye, or other dichotomous stem, as it would be if all the buds developed into branches, and compare it with your diagrams of excurrent and deliquescent growth. Draw diagrams to illustrate the branching of the elm, beech, lilac, linden, rose, maple, or their equivalents. 153. Definite and indefinite annual growth. — The presence or absence of ter- minal buds gives rise to another important distinction in plant development — that of definite and indefinite annual growth. Compare with any of the twigs just examined, a branch of rose, honey locust, sumac, mulberry, etc., and note the differ- ence in their modes of termination. The first kind, where the bough completes its season's increase in a definite time and then devotes its energies to developing a strong terminal bud to begin the next year's work with, are said to make a definite or determinate annual growth. Those plants, on the other hand, which make no provision for the future, but continue to grow till the cold comes and literally nips them in the bud, are indefinite, or in- determinate annual growers. Notice the effect of this habit upon their mode of branching. The buds toward the end of each shoot, being the youngest and tenderest, are most readily killed off by frost or other accident, and hence new branches spring mostly from the older and stronger buds near the base of the stem. It is their mode of branching that gives to plants of this class their peculiar bushy aspect. Such shrubs generally make good hedges on account of their thick undergrowth. The same effect can be produced arti- ficially by pruning. BUDS AND BRANCHES 137 FIQ. 156. — A mixed wood in winter, showing the trend of the branches. 154. Differences in the branching of trees. — We are now prepared to understand something about the causes of that endless variety in the spread of bough and sweep of woody spray that makes the winter woods so beautiful. Where the terminal bud is undisputed monarch of the bough, as in the pine and fir, or where it is so strong and vigor- ous as to overpower its weaker brethren and keep the lead, as in the magnolia, tulip tree, and holly, we have excurrent growth. In plants like the oak and apple, where all the buds have a more nearly equal chance, the lateral branches show more vigor, and the result is either deliquescent growth, or a mixture of the two kinds. In the elm and beech, where the usurping pseudo-terminal bud keeps the mastery, but does not completely overpower its fellows, we find the long, sweeping, delicate spray characteristic of those species. Examine a sprig of elm, and notice further that the flower buds are all down near the base of the stem, while the leaf buds are near the tip. The chief development of the season's growth is thus thrown toward the end of the branch, giv- m£ rise to tnat &UQ> feathery spray which makes the elm an even more beautiful object in winter than in summer (Fig. 158). An examination of the twigs of other trees will bring out the various peculiarities that affect then: mode of branching. The FIG. 157. — Winter spray of ash, an op- posite-leaved tree. 138 PRACTICAL COURSE IN BOTANY FIG. 158.— Winter spray of elm. angle, for instance, which a twig makes with its bough has a great effect in shaping the contour of the tree. Compare in this respect the elm and hackberry; the tulip tree and willow ; ash and hick- ory. As a general thing, acute angles produce slender, flowing effects; right or obtuse angles, more bold and rugged outlines. Practical Questions 1. Has the arrangement of leaves on a twig anything to do with the way a tree is branched? (145, 151,152.) 2. Why do most large trees tend to assume the excurrent, or axial, mode of growth if let alone? (150, 154.) 3. If you wished to alter the mode of growth, or to produce what nur- serymen call a low-headed tree, how would you prune it? (152, 153.) 4. Would you top a timber tree? (152, 153.) 5. Are low-headed or tall trees best for an orchard ? Why ? 6. Why is the growth of annuals generally indefinite ? 7. Name some trees of your neighborhood that are conspicuous for their graceful winter spray. 8. Name some that are characterized by sharpness and boldness of outline. 9. Account for the peculiarities in each case. II. BUDS MATERIAL. — Expanding leaf and flower buds in different stages of development ; large ones show the parts best and should be used where attainable. Some good examples for the opposite arrangement are horse-chestnut, maple, lilac, ash; for the alternate: hickory, sweet gum, balsam poplar, beech, elm. Where material is scarce, the twigs used in the last section may be placed in water and kept till the buds begin to expand. 155. Folding of the leaves. — Remove the scales from a bud of horse-chestnut nearly ready to open, and notice the manner in which the young leaves are folded. This is called vernation, or prefoliation, words meaning respectively " spring condition " and " condition preceding the leaf." Leaves are packed in the bud so as to occupy the least space possible, and in different plants they will be found folded in a great BUDS AND BRANCHES 130 ing bud of English wal- nut, showing twice con- duplicate vernation. FJG. 160. — A partly expanded leaf of beech, showing plicate- conduplicate vernation. many different ways, according to the shape and texture of the leaf and the space available for it in the bud. When doubled back and forth like a fan, or crum- pled and folded as in the buckeye, horse-chestnut, and maple, the vernation is plicate (Figs. 160, 162). 156. Position of the flower cluster. — What do you find . . within the circle of leaves : Examine one Qf the smaller axillary buds, and see if you find the same object within it. If you are in any doubt as to what this object is, examine a bud that is more expanded, and you will have no difficulty in recognizing it as a rudimentary flower cluster. Notice its position with refer- ence to the scales and leaves. If at the center of the bud, it will, of course, termi- nate its axis when the bud expands, and the growth of the branch will culminate in the flower. The branching of any kind of stem that bears a central flower cluster must, then, be of what order ? Compare your draw- ings with the section of a hyacinth bulb or jonquil, and note the similarity in position of the flower clusters. In a bud of the hick- a FIGS. 161,162. — Buds of maple : 161, vertical section of a twig ; 162, cross section through bud, showing folded leaves in center and scales surrounding them. FIG. 163. — Ver- tical section of hick- ory bud: a, furry in- ner scales; 6, outer scales ; I, folded leaf ; r, receptacle. 140 PRACTICAL COIJRSU IN KOTANY ory, walnut, oak, etc., the position of the flower clusters is different from that of flowers in the buds of lilac and horse-chest- nut. Look for a bud containing them, and find out where they occur. Can the axis con- tinue to grow after flowering, in this kind of stem ? Give a reason for your answer. Make sketches in transverse and longitudinal sec- tion (see Figs. 162, 163) of two different ,7 / £ kinds of buds, illustrating the terminal and axillary position of the flower cluster. 157. Dormant buds. — A bud may often lie dormant for months or even years, and then, through the injury or destruction of its stronger rivals, or some other favoring cause, develop into a branch. Such buds are said to be latent or dormant. The sprouts that often put up from the stumps of felled trees IK;. 164. — Twig originate from this source. 158. Supernumerarybuds.-Wlieremore i >M. I, i>; rs, ring of than one bud develops at a node, as is so scars left by last ri . . . i.u.i wales, often the case in the oak, maple, honey locust, etc., all except the normal one in the axil are supernumerary or accessory. These must not be con- founded with adventitious buds — those that occur elsewhere than at a node. Practical Questions 1. Would protected buds be of any use to annuals ? Why, or why not ? 2. Of what use is the gummy coating found on the buds of the horse- chestnut and balm of Gilead ? (148.) 3. Can you name any plants the buds of which serve as food for man ? 4. How do flower buds differ in shape from leaf buds? 5. At what season can the leaf bud and the flower bud first be dis- tinguished ? Is it the same for all flowering plants ? 6. Watch the different trees about your home, and see when the buds that are to develop into leaves and flowers the next season arc formed in each species. BIDS AND BRANCHES in III. THE BRANCHING OF FLOWER STEMS MATERIAL. — Typical flower clusters illustrating the dHinitc and indefinite modes of inflorescence,. Some of those mentioned in the text an- : Indefinite: hyacinth, shepherd's purse, \\:illllo\\ 189._ Twig of a hackberry (Cdtiscinerea), tical rOWS. The yUCCa showing the two-ranked arrangement. Notice how ~ , ,. the position of the stems and branches of the main Oleander, Canada flea- axis corresponds to that of the leaves. THE LEAF 151 PLATE. 9. — Vegetation of a moist, shady ravine. Notice the expanded surface of the leaf blades and the long internodes that separate the individual leaves. (From Rep't. Mo. Botanical Garden.) 152 PRACTICAL COURSE IN BOTANY FIG. 190. — Narrow leaves in crowded vertical rows. bane and bitterweed (Helenium tenuifolium) , illustrate this relation. On the other hand, when the leaves are large and rounded in outline, as those of , the sunflower, hollyhock, and catalpa, they are usually separated by longer internodes, or their blades are cut and incised so that the sun- light easily strikes through to the lower ones. 1 70 . Other external characteristics to be observed in leaves are : — whether round, oval, heart-shaped, (1) General Outline etc. (Figs. 191-197). (2) Margins: whether unbroken (entire), or variously toothed and indented. (Figs. 198-202.) 195 FIGS. 191-197. — Shapes of leaves : 191, lanceolate ; 192, spatulate ; 193, oval ; 194,obovate; 195, kidney-shaped ; 196, deltoid; 197,lyrate. (191-195 after GRAY.) (3) Texture: whether thick, thin, soft, hard, fleshy, leathery, brittle. (4) Surface: smooth, shining, dull, wrinkled, hairy, or otherwise roughened. THE LEAF 153 198 199 200 201 202 FIGS. 198-202. — Margins of leaves: 198, serrate; 199, den- tate ; 200, crenate; 201, undulate ; 202, sinuate. (After GRAY.) Not only do leaves of different kinds exhibit these characteristics in varying degrees, but young and old leaves, or those on young and old plants of the same kind, often differ from each other in color, size, shape, texture, mode of attachment, and the like, to such a degree (Figs. 203, 204) that one not familiar with them in both stages would hardly recognize them as belonging to the same species. The young leaves of eucalyptus, mul- berry, and some oaks afford conspicuous examples of such differences, and they exist between the cotyledons and ma- ture leaves of most plants. Can you see any benefit, in the case of the plant whose leaves you are study- ing, that could be derived from such of the characteristics named above as they may exhibit? 203 204 FIGS. 203,204. — Leaves of paper mulberry tree: 203, leaf from an old tree ; 204, leaf from a two-year- old sprout. Practical Questions 1 . Tell the nature and use of the stipules in such of the following plants as you can find : tulip tree ; fig ; beech ; apple ; willow ; pansy ; garden pea ; Japan quince (Pyrus Japonica) ; sycamore ; rose ; paper mulberry (Broitssonetia). 154 PRACTICAL COURSE IN BOTANY 2. How would you distinguish between a chinquapin, a chestnut, a chestnut oak, and a horse-chestnut tree by their leaves alone ? By their bark and branches ? Between a hickory, ash, common elder, box elder, ailanthus, sumach ? Between beech, birch, elm, hackberry, alder ? (Any other sets of leaves may be substituted for those named, the object being merely to form the habit of distinguishing readily the differences and resemblances among those that bear some general likeness to one another.) 3. From the study of these or similar specimens, would you conclude that resemblances in leaves are confined to those of closely related kinds ? 4. Name some causes independent of botanical relationship that might influence them. (169, 170; Exps. 48, 57.) 5. Do you find, as a general thing, more leaves with stipules or without ? 6. Is their absence from a mature leaf always a sign that it is really exstipulate? (166.) 7. Can you trace any line of development through intervening forms from a merely sessile leaf, like that of the pimpernel or specularia, to a peltate one ? (Figs. 184-187, and observation of living specimens.) 8. Does the leaf determine the position of the node, or the node the position of the leaf ? 9. Strip the leaves from a twig of one order of arrangement and replace them with foliage from a twig of a different order; for instance, place basswood upon white oak, birch upon lilac, elm upon pear, honeysuckle upon barberry, etc. Is the same amount of surface exposed as in the natural order ? 10. What disadvantage would it be to a plant if the leaves were arranged so that they stood directly over one another ? (169.) 11. Why are the internodes of vigorous young shoots, or scions, gen- erally so long ? (150.) 12. If the upward growth of a stem or branch is stopped by pruning, what effect is produced upon the parts below, and why? (152, 153.) 13. Give some of the reasons why corn grows so small and stunted when sown broadcast for forage? (60, 63, 169.) 14. What is the use of "chopping" (i.e. thinning out) cotton? II. THE VEINING AND LOBING OF LEAVES MATERIAL. — Leaves of any monocotyl and dicotyl will show the dif- ference between parallel and net-veining. To illustrate the palmate and pinnate kinds, the leaves of grasses and arums may be used for monocotyls, and for dicotyls, those of ivy, maple, grape, elm, peach, cherry, etc. ; for division, examine lobed and compound leaves of as many kinds as are attainable. A specimen showing each land of veining should be placed in THE LEAF 155 coloring fluid a short time before the lesson begins. The leafstalks of celery and plantain are excellent for showing the relation between the leaf veins and vascular system of the plant. 171. Parallel and net veining. — Compare a leaf of the wandering Jew, lily, or any kind of grass, with one of grape, ivy, or willow. Hold each up to the light, and note the veins or little threads of woody substance that run through it. Make a draw- ing of each so as to show plainly the direc- tion and manner of veining. Write under the first, parallel-veined, and under the second, net-veined. This distinction of leaves into parallel and net- veined cor- responds with the two great classes into which seed-bear- ing plants are divided, mon- ocotyls, as a general thing, FlG. 205. — Par- being characterized by the aUei-veined leaf of lily of the valley first kind, and dicotyls by (After GRAY). the second. 172. Pinnate and palmate veining. - FIG. 206. — Net- Next, compare a leaf of the canna, calla lily, veined leaf of a wil- Qr any km(J Qf arum, With One of the elm, peach, cherry, etc. What resemblances do you notice between the two ? What differ- ences? Which is parallel- veined and which is net-veined ? Make a drawing of each, and compare with the first two. Notice that in leaves of this kind, the petiole is continued in a large central vein, called the midrib, from which the secondary veins branch off on either side like the pinnae of a feather; whence such leaves are said to be pinnately, or feather veined, as in Figs. 206, 207. In the cotton, maple, ivy, etc., on the other hand, the petiole breaks up at the base of the FIG. 207.— Pi n- nateiy paraiiei- ** 156 PRACTICAL COURSE IN BOTANY FIG. 208. — Palmately net- veined leaf of wild ginger. leaf (Fig. 208) into a number of primary veins or ribs, which radiate in all directions like the fingers from the palm of the hand ; hence, such a leaf is said to be palmately veined. Net-veined leaves — the plantain (Fig. 209), wild smilax, beech, dog- wood — are sometimes ribbed in a way that might lead an inexperi- enced observer to confound them with parallel- veined ones, but the reticulations between the ribs show that they belong to the net-veined class. 173. Veins as a mechanical sup- port. — Hold up a stiff, firm leaf of any kind, like the mag- nolia, holly, or India rubber, to the light, having first scraped away a little of the under surface, and examine it with a lens. Compare it with one of softer texture, like the peach, maple, or clover. In which are the veins the closer and stronger? Which is the more easily torn and wilted ? Tear a blade of grass longitudinally and then cross- wise ; in which direction does it give way the more readily ? Tear apart gently a leaf of maple, or ivy, and one of elm or other pinnately veined plant; in which direction does each give way with least resistance? What would you judge from these facts as to the mechanical use of the veins ? 174. Effect upon shape. — By comparing a number of leaves of each kind it will be seen that the feather-veined ones tend to assume elongated outlines (Figs. 197, 207) ; the palmate-veined ones, broad and rounded forms (Figs. 195, 208). Notice also that the straight, unbroken venation of parallel- veined leaves is generally accompanied by smooth, unbroken margins, while the irregular, open meshes of net- veined leaves are favorable to breaks and indentations. FIG. 209. — Ribbed leaf of plantain. THE LEAF 157 175. "Veins as water carriers. — Examine a leaf from a stem that has stood in red ink for an hour or two. Do you see evidence that it has absorbed any of the liquid? Cut across the blade and examine with a lens. What course has the absorbed liquid followed? What use does this indicate for the veins, besides the one already noted? Observe the point of insertion on the stem, and examine the scar with a lens : do you see any evidence of a connection between the leaf veins and the fibro vascular bundles of the stem? (Ill, 125, 126. Notice where and how the veins end. Are they of the same size all the way, or do they grow smaller toward the tip? Are they separate and distinct, or are they con- nected throughout their ramifications, like the veins and arteries of the human body ? How do you know ? Do you see any of the coloring fluid in the small reticulations be- tween the veins? How did it get there? 176. The nature and office of veins. — We learn from 173 and 175 that the veining serves two important purposes in the economy of the leaf : first, as a skeleton or framework, to sup- port the expanded blade ; and second, as a system of water pipes, for conveying the sap out of which its food is manu- factured. In other words the veins are a continuation of the fibrovascular bundles into the leaves, by means of which the latter are put in communication with the body of the plant. 177. The relation between veining and lobing. — Com- pare the outline of a leaf of maple or ivy with one of oak or chrysanthemum. Do you perceive any correspondence be- tween the manner of lobing or indentation of then- margins, and the direction of the veins? (Figs. 210, 211.) To what class would you refer each one ? The lobes themselves may be variously cut, as in the fennel and rose geranium, thus giving rise to twice-cleft, thrice-cleft (Fig. 212), four-cleft, or even still more in- tricately divided blades. 178. Compound leaves. — Compare with the specimens just examined a leaf of horse-chestnut, clover, or Virginia 158 PRACTICAL COURSE IN BOTANY FIG. 210. — Pinnately lobed leaf of horse nettle. FIG. 211.— Palmately lobed leaf of grape. FIG. 212. — Palmately parted leaf of a buttercup. FIG. 213. — Pin- nately compound leaf of black locust. FIG. 214. — Palmately com- pound leaf of horse-chestnut. FIG. 215. — Pin- nately trif oliolate leaf of a desmodium. FIG. 216. — Pal - m a t e 1 y trifoliolate leaf of wood sorrel. THE LEAF 159 creeper, and one of rose, black locust, or vetch. Notice that each of these last is made up of entirely separate divisions or leaflets, thus forming a compound leaf. Notice also that the two kinds of compound leaves correspond to the two kinds of veining and lobing, so that we have palmately and pinnately compound ones. In pinnate leaves the continuation of the common petiole along which the leaflets are ranged is called the rhachis. Practical Questions 1. In selecting leaves for decorations that are to remain several hours without water, which of the following would you prefer, and why: smila^ or Madeira vine (Boussingaultia) ; ivy or Virginia creeper ; magnolia or maple; maidenhair or shield fern (Aspidium)? (173.) 2. Would you select very young leaves, or more mature ones, and why ? 3. Can you name any parallel- veined leaves that have their margins lobed, or indented in any way ? 4. Which are the more common, parallel- veined or net- veined leaves ? 5. Why do the leaves of corn and other grains not shrivel lengthwise in withering, but roll inward from side to side? (173.) 6. Can you name any palmately veined leaves in which the secondary veins are pinnate ? Any pinnately veined ones in which the secondary veins are palmate ? 7. Lay one of each kind before you ; try to draw a pinnate leaf with palmate divisions. Do you see any reason now why these so seldom occur in nature ? 8. Name some advantages to a plant in having its leaves cut-lobed or compound. (169.) 9. Mention some circumstances under which it might be advantageous for a plant to have large, entire leaves. (169; Plate 9.) 10. How would the floating qualities of the leaves of the pond lily be affected if their blades were cut-lobed or compound ? 11. Do the leaves of the red cedar and arbor vitae contribute to their value as shade trees ? 12. Name some of the favorite shade trees of your neighborhood ; do they, as a general thing, have their leaves entire, or lobed and compound ? 13. Which of the following are the best shade trees, and why : pine, white oak, mimosa (Albizzia), sycamore, locust, horse-chestnut, fir, maple, linden, China tree, cedar, ash ? 14. Which would shade your porch best, and why: cypress vine, grape, gourd, morning-glory, wistaria, clematis, smilax, kidney bean, Madeira vine, rose, yellow jasmine, passion flower? 160 PRACTICAL COURSE IN BOTANY HI. TRANSPIRATION MATERIAL. — Leafy twigs of actively growing young plants. Sun- flower, corn, peach, grape, calla, and arums in general transpire rapidly ; thick-leaved evergreens and hairy or rough species, like mullein and hore- hound more slowly. For Exp. 63, small-leaved, large-leaved, and thick- leaved kinds will be needed. APPLIANCES. — Glass jars and bottles with air-tight stoppers ; a little vaseline, oil, gardener's wax, thread, cardboard, and a pair of scales. EXPERIMENT 62. To SHOW WHY LEAVES WITHER. — Dry two self- sealing jars thoroughly, by holding them over a stove or a lighted lamp for a short time to prevent " sweating." Place in one a freshly cut leafy sprig of any kind, leaving the other empty. Seal both jars and set them in the shade. Place beside them, but without covering of any kind, a twig similar to the one in the jar. Both twigs should have been cut at the same time, and their cut ends covered with wax or vaseline, to prevent access of air. Look at intervals to see if there is any moisture deposited on the inside of either jar. If there is none, set them both in a refrigerator or cover with a wet cloth and allow to cool for half an hour, and then ex- amine again. In which jar is there a greater deposit of dew? How do you account for it ? Take the twig out of the jar and compare its leaves with those of the one left outside ; which have withered the more, and why ? EXPERIMENT 63. To MEASURE THE RATE AT WHICH WATER is GIVEN OFF BY LEAVES OF DIFFERENT KINDS. Fill three glaSS VCSSels of the same size with water and cover with oil to prevent evaporation. Insert into one the end of a healthy twig of peach or cherry ; into the second a twig of catalpa, grape, or any large-leaved plant, and into the third, one of magnolia, holly, or other thick-leaved evergreen, letting the stems of all reach well down into the water. Care must be taken to select twigs of approximately the same size and age, since the absorbent properties of very young stems are more injured by cutting and exposure than those of older ones. All specimens should be cut under water as directed in Exp. 58. Weigh all three vessels, and at the end of twenty- four hours, weigh again, taking note of the quantity of liquid that has dis- appeared from each glass. This will represent approximately the amount absorbed by the leaves from the twigs to replace that given off. Which twig has lost most? Which least? Note the condition of the leaves on the different twigs; have they all absorbed water about as rapidly as they have lost it ? How do you know this ? Pluck the leaves from each twig, one by one, lay them on a flat surface that has been previously measured off, into square inches or centimeters, and thus form a rough estimate of the area covered by each specimen. Make the best estimate THE LEAF 161 you can of the number of leaves on each tree, and calculate the number of kilograms of water it would give off at that rate in a day. EXPERIMENT 64. THROUGH WHAT PART OF THE LEAF DOES THE WATER GET OUT ? — Take some healthy leaves of tulip tree, grape, tropseolum, or any large, soft kind attainable. Cover with vaseline the leafstalk and upper surface of one ; the stalk and under surface of a second ; the stalk and both surfaces of a third, and leave a fourth one untreated. Suspend all four in a dry place by means of a thread attached to the petioles so that both surfaces may be equally exposed. The leaves must be all of the same species, and as nearly as possible of the same age, size, and vigor, and care must be taken that none of the vaseline is rubbed off in handling. Examine at intervals of a few hours. Which of the leaves withers soonest ? Which keeps fresh longest? From what part would you conclude, judg- ing by this experiment, that the water escapes most rapidly ? 179. Transpiration, nutrition, and growth. — We learn from the foregoing, and from Exps. 58 and 59, that plants give off moisture very much as animals do by perspiration. The two processes must not be classed together, however, for they are physiologically different. The action, in plants, is called transpiration. It is usually assumed that a large amount of water must pass through the plant in order to bring to it the necessary supply of food material ; but since the entrance of mineral salts is brought about by osmosis, conditioned by the living cells of the root; and since osmosis of salts may take place in a direction opposite to that of the greater movement of water, it follows that the entrance of salts is independent of transpiration. Inasmuch, however, as a certain amount of water is necessary to bring the living cells into a condition of turgor (7) so that they may grow, it follows that there is a relation between transpiration and growth. If transpiration exceeds absorption for any length of time, the tissues will be de- pleted of their moisture, as is shown by the wilting of crops in dry, hot weather; and if the unequal movement continues long enough, the plant will die. Hence, a knowledge of the laws governing this important function is necessary to all who are interested in cultivating agricultural products. 162 PRACTICAL COURSE IN BOTANY 180. Magnitude of the work of transpiration. — Few people have any idea of the enormous quantities of water given off by leaves. It has been calculated that a healthy oak may have as many as 700,000 leaves, and that 111,225 kilograms of water — equal to about 244,700 pounds — may pass from its surface in the five active months from June to October. At this rate 226 times its own weight may pass through it in a year, and it would transpire water enough during that time to cover the ground shaded by it to a depth of 20 feet!1 Lawn grass gives off water at such a rate that a va- cant lot of 150 X 50 feet, if well turfed, would be capable of trans- piring over a ton of water a day. Compare these figures with the average yearly rainfall in our Gulf States — 53 inches, approximately — and you can form some estimate of the injury done to a growing crop from this cause alone. The moisture is drawn from the surface by shallow rooted weeds (81) and dissipated through the leaves. In the case of forest trees the effect is different. Their roots, striking deep into the soil, draw up water from the lower strata and distribute it to the thirsty air in summer. FIG. 217. — A " weeping tree," showing the effect where absorption exceeds transpiration. Notice the position of the tree near the water where the roots have unlimited moisture. (After FRANCE.) 1 Marshall Ward, " The Oak." THE LEAF 163 As the water given off by transpiration is in the form of vapor, it must draw from the plant the amount of heat necessary for its vaporization, and thus has the effect of making the leaves and the air in contact with them cooler than the surrounding medium. At the same time the cool- ness and moisture of the air tend to check the loss by evaporation from the surface soil. It is partly to this cause, and not alone to their shade, that the coolness of forests is due. Measurements at various weather bureau stations in the United States show that in summer the temperature of oak woods is 4° C. lower during the day than in the open, and as much higher at night. In a beech wood in Germany the difference between the forest and the general tempera- ture amounted to as much as 7° C. Practical Questions 1. Is there any foundation in fact for the accounts of "weeping trees" and "rain trees" that we sometimes read about in the papers? (180; Exp. 48.) 2. Can you explain the fact, sometimes noticed by farmers, that in wooded districts, springs which have failed or run low during a dry spell sometimes begin to flow again in autumn when the trees drop their leaves, even>though there has been no rain? (180; Exp. 63.) 3. Other things being equal, which would have the cooler, pleasanter atmosphere in summer, a well-wooded region or a treeless one? (180.) 4. Could you keep a bouquet fresh by giving it plenty of fresh air? (Exp. 62.) 5. Why does a withered leaf become soft and flabby, and a dried one hard and brittle? (7; Exp. 62.) 6. Why do large-leaved plants, as a general thing, wither more quickly than those with small leaves? (Exp. 63.) 7. Is the amount of water absorbed always a correct indication of the amount transpired ? Explain. (179.) 8. Explain the difference between the withering caused by excessive transpiration and the shrinkage of cells due to plasmolysis. Are both of these physiological processes ? 9. Why is it best to trim a tree close when it is transplanted ? (179, 180.) 10. Why should transplanting be done in winter or very early spring, before the leaves appear ? (180.) 164 PRACTICAL COURSE IN BOTANY IV. ANATOMY OF THE LEAF MATERIAL. — For study of the epidermis, leaves of the white garden lily (Lilium album) are best, as the stomata can be seen on their lower surface with the naked eye. Wandering Jew, Spanish bayonet (Yucca aloifolia), anemone, narcissus, iris, canna, show them under a hand lens, but less distinctly. For sections, beet, mustard, and beech leaves may be used, or ready-mounted specimens obtained of a dealer. A compound microscope is needed for a minute study of the leaf structure. 181. Stomata. — It was shown in Exp. 64 that the water of transpiration escapes most rapidly, as a general thing, from the under surface of leaveg. To find out why this is so, a careful study of the epidermis will be necessary. For this purpose procure, if possible, the leaf of a white garden lily (Lilium album), wandering Jew, Spanish bayonet (Yucca aloifolia), anemone, narcissus, iris, or canna. The first- named is preferable, as the transpiration pores can be seen on it with the naked eye. Examine the under surface with a hand lens, and you will see that it is covered with small eye-shaped dots like those shown in 218 2w - Figs> 218 and 219' StriP off a P°rtion of stomata of white lily the epidermis, hold it up to the light on a opln.2 u/t0GdRiY2.)9' Piece of moistened glass, and they can be seen quite clearly with a lens. These dots are the pores through which the water vapor escapes. in transpiration, and through which air finds its way into the tissues of the leaf. They are called stomata (sing., stoma), from a Greek word meaning " a mouth." Look for stomata on the upper epidermis ; do you find any, and if so, are there as many as on the under surface ? Do you see any relation between this fact and the results obtained from Exp. 64? Can you see any good reasons why the stomata should be placed on the under side in preference to the upper ? Are they as much exposed to excessive light and heat, or as liable to be choked by dust, rain, and dew here as on the upper side ? THE LEAF 165 182. Distribution of stomata. — While stomata are gen- erally more abundant on the under side of leaves, this is not always the case. In vertical leaves, like those of the iris, which have both sides equally exposed to the sun, they are distributed equally on both sides. In plants like the water lily, where the under surface lies upon the water, they occur only on the upper side. Succulent leaves, as a general thing, have very few, because they need to conserve all their moisture. Submerged leaves have none at all ; why ? 183 . Minute study of a leaf epidermis. -Place a bit of the lower epidermis of FlG. 220.— A small a leaf under the microscope, and examine Piece of the under epider- .,, , . , T, .,, ... mis of an oak leaf , highly With a high power. It Will appear, if a magnified to show the monocotyl, to be composed of long, flat, *%£*£ °' and minute rectangular spaces (Fig. 221) ; if the leaf of a dicotyl is used, they will be more or less irregular (Fig. 220), with the outlines fitting into each other like the tiling of a floor or the blocks of a Chinese puzzle. These spaces are the cells of the epidermis, and the lines are the cell walls. Can you find any of the cell contents? The cell sap is not often visible ; do you see the nuclei ? Can you give a reason why the epidermal cells are so thin and flat ? Be- tween some of the cells you will see two kidney-shaped bodies placed with their concave sides together so as to leave a lenticular opening between them. This is a stoma, and the kidney-shaped bodies (Figs. 218, 219) are guard cells. They are given this name because they open or close the mouth of the stoma. If you will imagine a toy balloon made in the form of a hol- low ring, like the tire of a bicycle, you can easily see, from FIG. 221. — Under epidermis of an oat leaf, showing stomata. 166 PRACTICAL COURSE IN BOTANY FIG. 222. — Outline of a stoma of hellebore in vertical section. The darker lines show the shape assumed by the guard cells when the stoma is open ; the lighter lines, when the stoma is closed. The cavities of the guard cells with the stoma closed are shaded, and are distinctly smaller than when the stoma is open. Figs. 218, 219, that when the ring is strongly inflated, it will expand, and in enlarging its own circumference, will at the same time increase the. diameter of the opening in the center. When the ex- pansive force is removed, it collapses, thus closing, or greatly reducing, the aperture. In the same way the guard cells, when there is abundance of water in them, expand, thus open- ing the stoma so that the water vapor passes out more readily. But when there is a dearth of moisture, or when, by reason of chemical action in the soil, the roots fail to supply it, the leaves wither, the guard cells, losing their water, collapse, closing the pore, and trans- piration is thus prevented or greatly retarded. (Fig. 222.) Sketch a portion of the epidermis as it appears under the mi- croscope, labeling the parts. If stomata can be found in both conditions, make sketches showing them both open and closed. 184. Internal structure of a leaf. — Roll a leaf blade, or fold it tightly to facilitate cutting, and with a scalpel, or a very sharp razor, cut the thinnest possible slice through the roll. This will give a section at right angles to the epidermis. It should be so thin as to appear almost transparent. Put a small bit of a section in a drop of water on a slide, place under the microscope, using a high power, and look for the parts shown in Fig. 223. Notice the horizontally flattened cells of the upper epidermis, e, and of the lower epidermis, e'm, also the ver- tically elongated palisade cells, p, filled with particles of green coloring matter. These particles are the chlorophyll bodies, to which the green color of the leaf is due. They are the active agents in the manufacture of plant food, and in a leaf THE LEAF 167 removed from the plant during the day time and viewed under a high power, the chlorophyll bodies, on treatment P- Fbv ach Fbv FIG. 223. — Transverse section through a leaf of beet: e, upper epidermis; e', lower epidermis ; st, stoma ; a, air space ; p, palisade cells ; t, collecting cells ; sch, spongy parenchyma ; i, i, intercellular air spaces ; Fbv, section of a vein (fibrovascu- lar bundle). with iodine, will be seen to contain granules of starch which they are in the act of elaborating. The collecting cells, t, receive the assimilated product from the palisade cells and pass it on through the spongy parenchyma, sch, to the fibrovascular bundles. Notice how much more abundant the green matter is in the upper part of the leaf than in the lower ; has this anything to do with the deeper color of the upper surfaces , . 0 x/\. ,, . . ,, FIG. 224. — Chlo- of leaves? Notice the opening, st, in the rophyii bodies con- lower epidermis ; do you recognize it? (See ^^ course oTTor- Fig. 222.) It is a stoma, seen in vertical mation. Magnified section. Notice the intercellular air spaces, ^ i, i, in the spongy parenchyma, and the much larger one, a, just behind the stoma. Why is this last so much larger? 168 PRACTICAL COURSE IN BOTANY Sketch the section of your specimen as it appears under the microscope. It will perhaps differ in some details from \ the one shown in the figure, but you can recognize and label : the corresponding parts. Be sure that your drawing repre- sents accurately the relative size and shapes of the different kinds of cells. It is in the upper surface, where the chlorophyll particles abound, that the manufacture of food goes on most actively, and from the under surface, where the stomata are situated, that transpiration takes place and air and other gases pass to and from the interior. These facts have important bear- ings on the growth and external characters of leaves. Practical Questions 1. Explain why a plant cannot thrive if its stomata are clogged with foreign matter. (179; Exp. 64; 184.) 2. Mention some of the ways in which this might happen. (181.) 3. Why must the leaves of house plants be washed occasionally to keep them healthy? (179,181.) 4. Why is it so hard for trees and hedges to remain healthy in a large manufacturing town ? V. FOOD MAKING MATERIAL. — A sprig of pondweed, mare's-tail (Hippuris), hornwort (Ceratophyllum), marsh St.-John's-wort (Elodea), or other green aquatic plant ; bean or tropseolum, or other green leaves gathered from plants growing in the sunshine ; a healthy potted plant ; a small, fresh cutting. APPLIANCES. — A shallow dish of water and two glass tumblers or wide- mouthed jars ; a bent glass or rubber tube ; a piece of black cloth or paper ; a half pint of alcohol ; iodine solution ; a glass funnel or a long-necked bottle from which the bottom has been removed. EXPERIMENT 65. Is THERE ANY RELATION BETWEEN SUNLIGHT AND THE GREEN COLOR OF LEAVES? — Place a seedling of oats, or other rapidly growing shoot, in the dark for a few days, and note its loss of color. Leave it in the dark indefinitely, and it will lose all color and die. Hence we may conclude that there is some intimate connection between the action of light and the green coloring matter of leaves. EXPERIMENT 66. Do LEAVES GIVE OFF ANYTHING ELSE BESIDES WATER ? — Submerge a green water plant, with the cut end uppermost, in THE LEAF 169 a glass vessel full of water, and invert over it a glass funnel, or a long- necked bottle from which the bottom has been removed as directed in Exp. 53. Expel the air from the neck of the funnel — or bottle — by submerging and corking under water so as to make it air-tight. Place in the sunlight and notice the bubbles that begin to rise from the cut end of the plant. When they have partly filled the neck of the funnel, remove the stopper and thrust in a glowing splinter. If it bursts into flame, or glows more brightly, what is the gas that was given off? (Exp. 22.) As oxygen is not a product of respiration, some other process must be at work here, during which oxygen is set free, and some other substance used up. (Exps. 24 and 25.) EXPERIMENT 67. WHAT is THE SUBSTANCE TAKEN IN WHEN OXYGEN IS GIVEN OFF ? — Fill two glaSS jars, or two tumblers, with water, to expel the air, and invert in a shallow dish of water, having first introduced a freshly cut sprig of some healthy green plant into one of them. Then, by means of a bent tube, blow into the mouth of each tumbler till all the water is expelled by the impure air from the lungs. Set the dish in the sunshine and leave it, taking care that the end of the cutting is in the water of the dish. After forty-eight hours re- oxygen in sunlight. move the tumblers by running under the mouth of each, before lifting from the dish, a pie e of glass well coated with vaseline (lard will answer), and pressing it down tight so that no air can enter. Place the tumblers in an upright position, keeping them securely covered. Fasten a lighted taper or match to the end of a wire, plunge it quickly first into one tumbler, then into the other, and note the result. What was the gas blown from your lungs into the 226. — Experiment jars ? (Exps. 23, 24.) Why did the taper not for showing that leaves absorb go out in the second jar? What had become carbon dioxide from the at- ,. , , •, j- -j 0 mosphere. of the carbon dioxide ? EXPERIMENT 68. To SHOW THAT LIGHT IS NECESSARY FOR A PLANT TO ABSORB CARBON DIOXIDE AND GIVE OFF OXYGEN. — Repeat Exp. 66, keeping the plant in a dark or shady place; do you see any bubbles? Test with a glowing match; is any oxygen FIG. 225. — Experi- Fro. 170 PRACTICAL COURSE IN BOTANY formed in the tube of the funnel? Move back into the sunlight and leave for a few hours ; what happens when you thrust a glowing splinter into the tube ? EXPERIMENT 69. Is ANY FOOD PRODUCT FOUND IN LEAVES ? — Crush a few leaves of bean, sunflower, or tropseolum, and soak in alcohol until all the chlorophyll is dissolved out. Rinse them in water, and soak the leaves thus treated in a weak solution of iodine for a few minutes, then wash them and hold them up to the light. If there are any blue spots on the leaves, what are you to conclude ? If a test for sugar is to be made, use sap pressed from fresh leaves; for oils and fats, leaves should be dried without being placed in alcohol. EXPERIMENT 70. HAS THE PRESENCE OR ABSENCE OF LIGHT ANYTHING TO DO WITH THE OCCURRENCE OF STARCH IN LEAVES ? — Exclude the light from parts of healthy leaves on a grow- ing plant of tropaeolum, bean, etc., by placing patches of black cloth or paper over them. FIG. 227. — Leaf arranged Leave in a bright window, or preferably out of with a piece of tin foil to ex- doors, for several hours, and then test for starch elude light from a portion of as jn the jast experiment : do you find any in the surface. , . , , , the shaded spots r EXPERIMENT 71. Is THE PRESENCE OF AIR NECESSARY FOR THE PRODUCTION OF STARCH ? — Cover the blades and the petioles of several leaves with vaseline or other oily substance so as to exclude the air, and after a day or two test as before. 185. Influence of plants on the atmosphere. — These experiments show that leaves cannot do their work without light and air. The particular element of the atmosphere used by them in the process of food making is carbon dioxide. Their action in absorbing this gas and giving off oxygen tends to counterbalance the opposite action of respiration, decomposition, and combustion of all kinds, by which the proportion of it in the atmosphere tends to be constantly increased. In this way they help to regulate the quantity of it present and have a beneficial effect in ridding the air of one source of impurity. THE LEAF 171 186. Photosynthesis. — In our examination of the internal structure of the leaf, the chlorophyll bodies (184) were found to contain small granules of starch which the chlorophyll, under the stimulus of light, had elaborated as a nutriment for the plant tissues. Hence, the leaf may be regarded as a factory in which vegetable food, mainly starch, is manufac- tured out of the water brought up from the soil, and the carbon dioxide derived through the stomata from the atmosphere. In this process carbon dioxide (CO2) is combined with water (H20) in such proportions that part of the oxygen is returned to the surrounding air. This is a fundamental food-forming process' characteristic of green plants, and can take place only in the light. For this reason it has been named Photo- synthesis, a word which means " building up by means of light," just as photography means " drawing or engraving by means of light." In carrying on the operation of photosynthesis, sunshine is the power, the chlorophyll bodies the working machinery, carbon dioxide and water the raw materials, and starch or oil the finished product, while oxygen and the water of trans- piration represent the waste or by-products. 187. How the new combination is effected. — It may seem strange that a gas and a liquid should combine to make something so different from either as starch, but their chemi- cal constituents are the same in different proportions. Water is made up of 2 parts hydrogen and 1 part oxygen; carbon dioxide, of 1 part carbon and 2 parts oxygen, while starch contains carbon, hydrogen, and oxygen, in the ratios of 6, 10, and 5, respectively. Hence, by taking sufficient quanti- ties of water and carbon dioxide and combining them in the proper proportions, the leaf factory can turn them into starch. If we use the letters C, H, and O, to represent Car- bon, Hydrogen, and Oxygen, respectively, the new combina- tion of materials can be expressed by an equation; thus: — water carbon dioxide starch by-products 5(H20) -f 6(C02) = (CeHioOe) + 6 (02) = 12(0). 172 PRACTICAL COURSE IN BOTANY The water not used up in the process is given off as a waste product in transpiration, while the oxygen is returned to the air, as shown by Exp. 66. This equation is not to be under- stood as representing the chemical changes that actually take place in the leaf. These are too complicated, and at present too imperfectly known, to be considered here. It will serve, however, to give a fair idea of the final result from the process of photosynthesis, however brought about. Simple as the operation appears, the chemist has not, as yet, been able to imitate it. He can analyze starch into its original constituents, but while he has the ingredients at hand in abundance, and knows the exact proportions of their combination, it is beyond his power, in the present state of our knowledge, to put them together. Hence, both man and the lower animals are dependent on plants for this most important food element. The so-called factories that supply the starch of commerce do not make starch any more than the miller makes wheat, but merely separate and render available for use that already elaborated by plants. 1 88. Proteins. — Foods of this class are mainly instru- mental in furnishing material for the growth and repair of the tissues out of which the bodies of both plants and animals are built up. They embrace a great variety of substances, but their chemical nature is very complex and very imper- fectly understood. Nitrogen is an important element in their composition, whence they are commonly distinguished as " nitrogenous foods." Besides nitrogen, there are present carbon, hydrogen, oxygen, and sulphur, and traces of the mineral salts absorbed from the soil are found in varying quantities in the ash of different proteins. The percentages in which these ingredients are combined and the processes concerned in their formation are at present a matter of pure hypothesis. Botanists are not agreed even as to whether they are made in the leaf or in some other part or parts of the plant, though the weight of opinion inclines to the view that their construction takes place in the leaf. THE LEAF 173 189. The activities of leaves. — As there are only 4 parts of CO2 to every 10,000 parts of ordinary free air, it has been estimated that in order to supply the leaf factory with the raw material it needs, an active leaf surface of one square meter — a little over one square yard — uses up, during every hour of sunshine, the CO2 contained in 1000 liters (1000 quarts, approximately) of ah-. Suppose an oak tree to bear 500,000 leaves, each having a surface of 16 sq. cm., or 4 sq. in., and working 12 hours a day for 6 months in the year; you will then have some idea of the enormous quantity of air thafpasses each season through its leaf system. Add to this the almost incredible volume of water transpired in the same time (180), and we may well stand amazed at the tremendous activities of these silent workers that we are in the habit of regarding as mere passive elements in the general landscape. 190. The economic value of leaves. — Besides their im- portance as sanitary and food-making agencies, leaves have a direct commercial value as food products in the hay and fodder they supply for our domestic animals, the tea and salads with which they provide our tables, the aromatic flavors and seasonings contained in them, and the drugs, medicines, and dyes of various kinds for which they furnish the ingredients. Practical Questions 1. Why do gardeners "bank" celery? (Exp. 65.) 2. Why are the buds that sprout on potatoes in the cellar, white ? (Exp. 65.) 3. Why does young cotton look pale and sickly in long-continued wet or cloudy weather? (Exp. 65.) 4. Why do parasitic plants generally have either no leaves or very small, scalelike ones? (85, 186, 187.) 5. The mistletoe is an exception to this; explain why, in the light of your answer to question 4. 6. Could an ordinary nonparasitic plant live without green leaves? (186, 187.) 7. Are abundance and color of foliage any indication of the health of a plant? (166, 187; Exp. 65.) 174 PRACTICAL COURSE IN BOTANY 8. Is the practice of lopping and pruning very closely, as in the process called "pollarding," beneficial to a tree under ordinary conditions ? (186, 189; Exp. 63.) 9. Name some plants of your neighborhood that grow well in the shade. 10. Compare in this respect Bermuda grass and Kentucky blue grass ; cotton and maize; horse nettle (Solanum Carolinense] and dandelion; beech, oak, red maple, dogwood, pine, cedar, holly, magnolia, etc. 11. Name all the aromatic leaves you can think of ; all that are used as food, beverages, drugs, and dyes. 12. What is the use of aromatic and medicinal leaves to the plant itself ? (Suggestion: Why does the housewife put lavender or tobacco leaves in her woolen chest ?) 13. Which would be richer in nourishment, hay cut in the evening or in the morning, and why? (54, 186; Exp. 70.) 14. Mention three important sanitary services that are rendered by a tree like that shown in plate 6 or 8. (180, 185, 189.) 15. Name some of the plants employed in the manufacture of starch. VI. THE LEAF AN ORGAN OF RESPIRATION MATERIAL. — A number of vigorous, freshly cut green leaves ; a liter or two (one or two quarts) of expanding flower or leaf buds. APPLIANCES. — -Some wide-mouthed jars of one or two liters' capacity; two small open vials of limewater. EXPERIMENT 72. Do LEAVES GIVE OFF CARBON DIOXIDE ? — Cover the bottoms of two wide-mouthed jars with water about two centimeters (1 inch) deep. Place in one a number of healthy green leaves with their stalks in the water, and insert among them a small open vial con- taining limewater. In the other jar place only a vial of limewater in the clear water at the bottom, this last being merely to make the conditions in both vessels the same. Seal both tight and keep together in the dark for about 48 hours, and then examine. In which jar does the lime- water indicate the greater accumulation of C02 ? (It may show a slight milkiness in the other vessel due to gas derived from the inclosed air and water.) From this experiment, what process would you conclude has been going on among the leaves in jar No. 1 ? (Exp. 25.) EXPERIMENT 73. Is THE EXHALATION OF CARBON DIOXIDE ACCOM- PANIED BY ANY OTHER CONCOMITANT OF RESPIRATION ? In ExpS. 24, 25, it was shown that respiration is accompanied by heat ; hence, if the production of carbon dioxide by the leaf is due to this cause, it should be attended by the evolution of heat. To find out whether this is the case, partly fill a glass jar of two liters' capacity with unfolding 1'eaf buds ar- THE LEAF 175 Fio. 228. — Arrange- ment of apparatus to ranged in layers alternating with damp cotton bat- ting or blotting paper (Fig. 228) ; close the jar tightly and leave from 12 to 24 hours in the dark to prevent the action of photosynthesis. Then insert a thermometer and note the rise in tem- perature. If a lighted taper is plunged in, it will quickly be extinguished, showing that respiration has been going on. 191. Respiration in leaves. — We see from experiments like the foregoing that the leaf, besides carrying on the functions of digestion, photosynthesis, and trans- piration, is also an active agent in the work of respiration. In this function by leaf buds. oxygen is used up and carbon dioxide given off, just as in the respiration of animals; but the process is so slow in plants that it is much more difficult to detect than the contrary action in photosynthesis, and is, in fact, not perceptible at all while the latter is going on, though it does not cease even then. But while the leaf is the principal organ of respiration, the process is carried on in other parts of the plant as well, else it could not survive during the leafless months of winter. It appears to be most active at night, but this is only because it is not obscured then, as during the day, by the more active function of photosynthesis. Indeed, it was for a long time supposed that plants " breathed " only at night, and it was thought to be unwholesome to keep them in a bedroom. It is now known, however, that respiration goes on at all times and in all living parts of the plant, but the quantity of oxygen taken in is so small from a hygienic point of view that it may be disregarded. 192. Distinctions between respiration and photosynthesis. - While these two functions are contrasting and antipodal, so to speak, in their action, they are mutually complemen- tary and interdependent, the one manufacturing food and the other using it up, or rather marking the activity of those 176 PRACTICAL COURSE IN BOTANY life processes by which it is used up. The difference between them will be made clear by a comparison of the two pro- cesses as summarized in the following statement : PHOTOSYNTHESIS RESPIRATION Goes on only in sunlight and in Goes on at all times and in all the green parts of plants. parts of the plant. Produces starch and sugar. Releases energy (heat and wo k- ing power). Gives off, as by-product, oxygen. Gives off, as by-products, C02 and water. A constructive process, in which A destructive, or consumptive energy is used up to make food. process, in which food is used up in expending energy. 193. Metabolism. --The total of all the life processes of plants, including growth, waste, repair, etc., is summed up under the general term metabolism. It is a constructive or building-up process when it results in the making of new tissues out of food material absorbed from the earth and air, and the consequent increase of the plant in size or numbers. But, as in the case of animals, so with plants, not all the food provided is converted into new tissue, part being used as a source of energy, and part decomposed and excreted as waste. In this sense, metabolism is said to be destructive. The waste in healthy growing plants is always, of course, less than the gain, and a portion of the food material is laid by as a reserve store. For this reason, photosynthesis, being a constructive process, is usually more energetic than respira- tion, which is the measure of the destructive change of materials that attends all life processes. It is evident also, from what has been said, that growth and repair of tissues can take place only so long as the plant has sufficient oxygen for respiration, since the energy liberated by it is necessary for the assimilation of nourishment by the tissues. Thus we see that plants are dependent on air not only for respiration, but for nutrition, and none of their life pro- cesses can be carried on without it. THE LEAF 177 Practical Questions 1. Can a plant be suffocated, and if so, in what ways? (87, 193; Exps. 26, 27.) 2. The roots on the palm shown in plate 3 are not drawing any sap from it as parasites; why does their continued growth bring about the death of the tree ? (87, 193.) 3. Is it unwholesome to keep flowering plants in a bedroom? Leafy ones? Why, in each case ? (191.) 4. Would there be any more reason for objecting to the presence of flowers by night than by day ? Explain. (191.) 5. Why is respiration much less marked in plants than in animals? (30, 31.) VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL RELATIONS MATERIAL. — A potted plant of oxalis, spotted medick, white clover, or other sensitive species. The subject is better suited for outdoor ob- servation than for laboratory work. EXPERIMENT 74. To SHOW THAT LEAVES ADJUST THEMSELVES TO CHANGES IN INTENSITY OF LIGHT. — Keep a healthy potted plant of oxalis, white clover, or spotted medick in your room for observation. Note the daily changes of position the leaves undengo. Sketch one as it appears at night and in the morning. In order to determine whether these changes are due to want of light or of warmth, put your plant in a dark closet in the middle of the day, with- out change of temperature. After several hours note results. Transfer FIGS. 229, 230. — Leaves of a peanut to a refrigerator, or in winter place P|ant: 22?' ** day P°sitionJ 230> in . . , . , •. -11 u night position, outside a window where it will be ex- posed to a temperature of about 5° C. (40° F.) for several hours, and see if any change takes place. Next put it at night in a well-lighted room and note the effect. If practicable, keep a specimen for several weeks in some place where electric lights are burning continuously all night, and watch the results. EXPERIMENT 75. To SHOW THAT THE FALL OF THE LEAF MAY RESULT FROM OTHER CAUSES THAN COLD OR FROST. — Wrap some leaves of ailan- thus, Kentucky coffee tree, ash, walnut, or hickory in a damp towel and 178 PRACTICAL COURSE IN BOTANY keep them in the dark for several days ; the leaflets will fall away, leaving a clear scar like those on winter twigs. EXPERIMENT 76. To SHOW THAT ADJUSTMENTS TO TEMPERATURE MAY BE MADE BY CHEMICAL MEANS. — Place a small twig of oleander, laures- tinus, or other broad-leaved evergreen in a 5 to 10 per cent solution of sugar, and transfer it at the end of a few days to a temperature of 6° to 8° below freezing. On comparison with a similar twig that has stood for the same length of time in pure water, it will be found to possess a greater power of resistance to cold. 194. The light relation. — The principal external con- ditions to which leaves have to adjust themselves are light, air, moisture, gravity, temperature, and the attacks of ani- mals. From the knowledge of their work and function gained in the preceding sections, it will be clear that the pri- mary relation of the leaf is a light relation, and to this, first of all, it must adjust itself. It was shown in Exps. 56 and 57 how promptly leaves re- spond to changes in the direction of light, and a little observation (Exp. 74) will con- vince us that they are equally sensitive to changes in intensity and periodicity of illu- mination. 195. Phototropism. - - The movement of plants in response to light is called photo- tropism — a word that means " turning FIG. 231. — A toward or away from light. " It includes plant that has been jj fo^fa f ft^t adjustments, and examples growing near an open t . . window, showing the of it are to be met with everywhere in the toward ^he^Hght!11 l disposition of leaves with reference to their light exposure. 196. Horizontal and vertical adjustment. - - Take two sprigs, one upright, the other horizontal, from any convenient shrub or tree — and notice the difference in the position of the leaves. Examine their points of attachment and see how this is brought about, whether by a twist of the petiole or of the base of the leaf blades, or by a half twist of the stem between two consecutive leaves, or by some other means. THE LEAF 179 PLATE 10. — A mosaic of moonseed leaves, showing adjustment for light exposure. (From Mo. Botanical Garden Rep't.) 180 PRACTICAL COURSE IN BOTANY Observe both branches in their natural position ; what part of the leaf is turned upward, the edge or the surface of the blade? Change the position of the two sprigs, placing the vertically growing one horizontal, and the horizontal one vertical. What part of the leaves is turned upward in each ? 232 233 FIGS. 232, 233. — Adjustment of leaves to different positions : 232, upright ; 233, procumbent. 197. Leaf mosaics. - - Trees with horizontal or drooping branches, like the elm and beech, and vines growing along walls or trailing on the ground, generally display their foliage in flat, spreading layers, each leaf fit- ting in between the interstices of the others like the stones in a mosaic, whence this has been called the mosaic arrangement. (Plate 10.) In plants of more upright or bunchy habit, the leaves are placed at all angles, giving the appearance of a rosette when viewed from above, whence this is called the rosette arrangement. A variety of the same disposition is seen in the pyramidal shape assumed by plants with large, undivided leaves like the mullein and burdock (Fig. 237), in which access of light is secured by a mutual adjustment between the size and position of leaves, the upper ones becoming successively smaller. FIG. 234. — Leaf mosaic of elm. THE LEAP 181 198. Heliotropism- " turning with the sun" - —is the name given to the daily movement of plants like the cotton and sunflower in turning their leaves or their 235 236 FIGS. 235, 236. — Horse-chestnut leaves: 235, leaf rosette seen from above; 236, the same seen sidewise, showing the formation of rosettes by the lengthening of the lower petioles. blossoms to face the sun. If you live where cotton is grown, notice the leaves in a field about ten o'clock on a bright sunny morning, and again from the same point of view at about four or five in the afternoon. Do you perceive any differ- ence in their general dis- position? Watch on a cloudy day and see if any change takes place. Find out by observation whether the " heliotrope " of the hothouses is really helio tropic. 199. Adjustment against too great intensity of light. — Plants fre- FIGS. 238, 239.— A .-, v , , compass plant, rosin- quently have to protect we e| (Sil;Mum ladni. . themselves against excess