A Practical Course in Botany

Chapter X. Cryptogams

I. THEIR PLACE IN NATURE 296

II. ALGÆ 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 necessary. “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 sections 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.

=1. 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 substances 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.

=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 independent existence. But the young plant, like the young animal, is incapable of providing for itself at first, and would die unless it received nourishment from the mother plant until it has formed roots and leaves so that it can manufacture food for 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 contained 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 classes of food 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 occurs in the form of globules. It is very abundant in some seeds, e.g. flax, castor bean, and Brazil nut. In the corn grain it is found in the part constituting 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 proteins are called aleurone 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 nutritious 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.

=4. Organic foods.=—These four substances, starch, sugar, fats, and proteins, with some others of less frequent occurrence, are called organic foods, because they are produced, in a state of nature, only through the action of organized living bodies, or, more strictly speaking, of 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 dependent 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 inclosing 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 individual 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 in mature ones, like the large one on the 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 mechanical 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 herbaceous plants and the tender parts of woody ones. This 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.

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