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.

=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 reduced 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 germinating 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 sometimes, 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 appearance, owing to their greater loss of water in drying.

=10. Food tests.=—In order 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 experiment 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.

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 potassium 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 substance 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; (b) 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 separate 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.

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?

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 them lightly to see if water comes out, and where. Place a number 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 GERMINATION 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 ABSORBING WATER?—Fill a common six-ounce bottle as full as it will hold with dry peas, beans, or 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 before? (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 clipped, 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.

=11. 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 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 cotyledon.” 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 compose 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 before. 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 examination because they are large and easy to handle, can be obtained everywhere, and germinate readily.

=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 diameter 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 longitudinally, and the small round object between the halves at one end; can you tell what it is?

Slip 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 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 appears under the lens. Open the plumule with a pin and examine 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 completely 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 protuberances 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 protuberance at the apex, caruncle. The caruncle is an appendage of the seed-covering developed by various plants; its use is not always clear. What appears to be its object in the castor bean? Refer to Exp. 13 and see if there is any other 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 caruncle. 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 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, dividing it into two halves, represents? Make a similar sketch of a cross section. Notice the same white line running horizontally across the endosperm, dividing it into two equal parts. To find out what these lines are, take another 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 embryo 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 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 relation whatever to the true beans. It belongs to the spurge family, which is botanically very remote from that of the peas and beans.

=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 together 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 remove the hard coat, or testa, as it is called. The thin, greenish 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, labeling 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 cotyledons 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 projection 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 substances; 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 recognize 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 seed borne on the inner side of a cone scale, without a pod or husk or outer covering of any kind, such as beans and nuts and grains are provided with. Plants like the pine, which bear their seed in this way, are called 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 consist of one or more layers? Is there any difference in color 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 appendages 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 examined? Pick out the embryo from the endosperm and test both for food substances. Which of these do you find? Which are absent? How does the embryo differ from those already examined? 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 examined. 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.

MODEL FOR RECORD OF SEEDS EXAMINED

+================+===========================================+ | | FOODS TESTED | | SEEDS EXAMINED +----------+----------+----------+----------+ | | Starch | Sugar | Oil | Proteins | +----------------+----------+----------+----------+----------+ | Corn | | | | | +----------------+----------+----------+----------+----------+ | Wheat | | | | | +----------------+----------+----------+----------+----------+ | Bean | | | | | +----------------+----------+----------+----------+----------+ | Squash | | | | | +----------------+----------+----------+----------+----------+ | Castor bean | | | | | +----------------+----------+----------+----------+----------+ | Pine | | | | | +----------------+----------+----------+----------+----------+

By far the greater number of seeds contain endosperm; that is, they consist of an embryo with more or less nourishing 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 germination.

=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 cotyledons of the bean, acorn, squash, etc., or packed about them in 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 one, two, or many cotyledons. The first two kinds make up the great class of Angiosperms, which includes all the true flowering plants and forms the most important part of the vegetation 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 in past ages, numbering only about four hundred known species, they present many diversities of form, which seem to ally them on the one hand with the lower, or spore-bearing plants (ferns, mosses, etc.), and on the other hand with the Angiosperms.

Practical Questions

1. Make a list of all the seeds you can find that have very thick cotyledons, and underline those that are used as food by man or beast.

2. Make a similar list of all the kinds with thin cotyledons and more or less endosperm, that are used 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 what part 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.)

7. What is bran? Does it contain any nourishment? (11, 12; Exps. 1-6.)

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 starch 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 aërial 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?

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?

=19. Agencies of dispersal.=—The means at nature’s disposal 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, including man. The first three are purely mechanical. The last, animal agency, is either voluntary or involuntary, according as it is conscious and intentional, or accidental merely. Man, of course, is the only consciously voluntary agent. Of the four agencies named, animals and wind are the most effective, 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 a squirrel buries nuts for his own use and then forgets the location 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 involuntary, but often unwilling agents of dispersal. Some of the most troublesome weeds of civilization have been unwittingly distributed by man as he journeyed from place to place, carrying, along with the seed for planting his crops, the various weed seeds, or “screenings,” as these 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 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 swallowed whole, compelling the animal, by their hardness or disagreeable flavor, to reject them. In cases where the seeds themselves are edible 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 hickory nut and walnut. The acidity or other disagreeable qualities 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 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 season 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 oxeye daisy, the rib grass, mayweed and bitterweed, possess very imperfect natural means of dispersal, and are largely dependent 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 adaptations for this purpose being connected 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 transportation. Such plants generally grow in light soils and either have very light root systems, or are easily broken from their anchorage and left to drift about on the ground. The spreading, 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 securing 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 required 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 till it strikes a soft spot, when it begins at once to bore its way into the ground. The common peanut is another example. 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, 23; Exp. 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; jimson weed; 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.)

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 different 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 arrangement 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.