Outlines of Lessons in Botany, Part I; from Seed to Leaf · Chapter 3Seedlings
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1. Directions for raising in the Schoolroom.—The seeds should be planted in boxes tilled with clean sand. Plates or shallow crockery pans are also used, but the sand is apt to become caked, and the pupils are likely to keep the seeds too wet if they are planted in vessels that will not drain. The boxes should be covered with panes of glass till the seedlings are well started, and should be kept at a temperature of from 65° to 70° Fahr. It is very important to keep them covered while the seeds are germinating, otherwise the sand will be certain to become too dry if kept in a sufficiently warm place. Light is not necessary, and in winter time the neighborhood of the furnace is often a very convenient place to keep them safe from frost. They should not be in the sun while germinating. When the first sprouts appear above the ground let another set be planted, and so on, till a series is obtained ranging from plants several inches high to those just starting from the seed. The seeds themselves should be soaked for a day and the series is then ready for study. The time required for their growth varies according to the temperature, moisture, etc. Dr. Goodale says they should be ready in ten days.[1]
I have never been able to raise them so quickly in the schoolroom, nor have the pupils to whom I have given them to plant done so at home. Generally, it is three weeks, at least, before the first specimens are as large as is desirable.
Germinating seeds need warmth, moisture and air. The necessary conditions are supplied in the very best way by growing them on sponge, but it would be difficult to raise enough for a large class in this manner. Place a piece of moist sponge in a jelly-glass, or any glass that is larger at the top, so that the sponge may not sink to the bottom, and pour some water into the glass, but not so much as to touch the sponge. The whole should be covered with a larger inverted glass, which must not be so close as to prevent a circulation of air. The plants can thus be watched at every stage and some should always be grown in this way. The water in the tumbler will keep the sponge damp, and the roots, after emerging from the sponge, will grow well in the moist air. Seeds can also be grown on blotting paper. Put the seeds on several thicknesses of moist blotting paper on a plate, cover them with more moist paper, and invert another plate over them, taking care to allow the free entrance of air.
If possible, it is by far the best way to have the seeds growing in the schoolroom, and make it a regular custom for the pupils to observe them every morning and take notes of their growth.
These lessons on seeds are suitable for pupils of every age, from adults to the youngest children who go to school. The difference should be only in the mode of treatment; but the same principles should be brought out, whatever the age and power of comprehension of the pupil.
For these lessons the following seeds should be planted, according to the above directions:
Morning-Glory, Sunflower or Squash, Bean, Pea, Red Clover, Flax, Corn, Wheat, and Oats.[1] If they can be procured plant also acorns, Pine-seeds, Maple-seeds, and horsechestnuts.
2. Study of Morning-Glory, Sunflower, Bean, and Pea.—For reasons hereafter given, I consider the Morning-Glory the best seedling to begin upon. Having a series, as above described, before them, the pupils should draw the seedlings. When the drawings are made, let them letter alike the corresponding parts, beginning with the plantlet in the seed, and using new letters when a new part is developed. The seed coats need not be lettered, as they do not belong to the plantlet.
[Illustration: FIG. 5.—Germination of Morning Glory, a, caulicle; b, cotyledons; c, plumule; d, roots.]
[Illustration: FIG. 6.—Germination of Sunflower.]
After drawing the Morning-Glory series, let them draw the Sunflower or Squash in the same way, then the Bean, and finally the Pea. Let them write answers to the following questions:
MORNING-GLORY.[1]
Tell the parts of the Morning-Glory seed.
What part grows first?
What becomes of the seed-covering?
What appears between the first pair of leaves?
Was this to be seen in the seed?
How many leaves are there at each joint of stem after the first pair?
How do they differ from the first pair?
SUNFLOWER OR SQUASH.
What are the parts of the seed?
What is there in the Morning-Glory seed that this has not?
How do the first leaves change as the seedling grows?
BEAN.
What are the parts of the seed?
How does this differ from the Morning-Glory seed?
How from the Sunflower seed?
How do the first pair of leaves of the Bean change as they grow?
How many leaves are there at each joint of stem?[1]
How do they differ from the first pair?
PEA.
What are the parts of the seed? Compare it with the Morning-Glory, Sunflower, and Bean.
How does it differ in its growth from the Bean?
What have all these four seeds in common?
[Illustration: FIG. 7.—Germination of Pea. a, caulicle; b, cotyledons; c, plumule; d, roots.]
[Illustration: FIG. 8.—Germination of Bean.]
What has the Morning-Glory seed that the others have not?
What have the Bean and Pea that the Morning-Glory has not?
How does the Pea differ from all the others in its growth?
What part grows first in all these seeds?
From which part do the roots grow?
What peculiarity do you notice in the way they come up out of the ground?[1]
The teacher must remember that, unless the pupils have had some previous training, they will first have to learn to use their eyes, and for this they will need much judicious help. They should be assisted to see what is before them, not told what is there. It is absolutely necessary that these questions should be thoroughly understood and correctly answered before any conclusions are drawn from them. For this purpose abundant material is indispensable. It is better not to attempt these lessons on seeds at all, unless there is material enough for personal observation by all the pupils.
After this preliminary work has been done, the names of the parts can be given to the pupils. They may be written under each drawing thus,—A=Caulicle;[1] B=Cotyledons; C=Roots; D=Plumule. The whole plantlet in the seed is the embryo or germ, whence the sprouting of seeds is called germination.
I consider this the best order to study the seeds because in the Morning-Glory the cotyledons are plainly leaves in the seed; and in the Squash or Sunflower[1] the whole process is plainly to be seen whereby a thick body, most unlike a leaf, becomes an ordinary green leaf with veins.[2] In the Sunflower the true leaves are nearly the same shape as the cotyledons, so that this is an especially good illustration for the purpose. Thus, without any hint from me, my pupils often write of the Bean, "it has two thick leaves and two thin leaves." In this way the Bean and Pea present no difficulty. The cotyledons in the first make apparently an unsuccessful effort to become leaves, which the second give up altogether.
The teacher's object now is to make the pupils understand the meaning of the answers they have given to these questions. In the first place, they should go over their answers and substitute the botanical terms they have just learned for the ones they have used.
COMPARISON OF THE PARTS OF THE SOAKED SEEDS.
Morning-Glory. A seed covering. Some albumen. Two cotyledons. A caulicle.
Sunflower. An outer covering.[1] An inner covering. Two cotyledons. A caulicle.[2]
Bean. A seed covering. Two cotyledons. A caulicle. A plumule.
Pea. The same as the Bean.
They have also learned how the first leaves in the last three differ from those of the Morning-Glory, being considerably thicker in the Sunflower, and very much thicker in the Bean and Pea. Why should the Morning-Glory have this jelly that the others have not? Why do the first leaves of the Sunflower change so much as the seedling grows? What becomes of their substance? Why do those of the Bean shrivel and finally drop off? By this time some bright pupil will have discovered that the baby-plant needs food and that this is stored around it in the Morning-Glory, and in the leaves themselves in the others. It is nourished upon this prepared food, until it has roots and leaves and can make its own living. The food of the Morning-Glory is called albumen; it does not differ from the others in kind, but only in its manner of storage.[1]
Also the questions have brought out the fact that the Bean and Pea have the plumule ready formed in the seed, while the Morning-Glory and Sunflower have not. Why should this be? It is because there is so much food stored in the first two that the plumule can develop before a root is formed, while in the others there is only nourishment sufficient to enable the plantlet to form its roots. These must make the second leaves by their own labor.
3. Comparison with other Dicotyledons.—The pupils should now have other seeds to compare with these four. Let them arrange Flax, Four o-clock, Horsechestnut, Almond, Nasturtium, Maple-seeds, etc., under two heads.
They may also be divided into those with and without the plumule.
Those with plumules will be seen to have the most abundant nourishment. In many cases this is made use of by man.
These last can be again divided into those in which the cotyledons come up into the air and those where they remain in the ground.
In the latter the cotyledons are so heavily gorged with nourishment that they never become of any use as leaves. As Darwin points out, they have a better chance of escaping destruction by animals by remaining in the ground.
The cotyledons are very good illustrations of the different uses to which a single organ may be put, and the thorough understanding of it will prepare the pupils' minds for other metamorphoses, and for the theory that all the various parts of a plant are modified forms of a very few members.
4. Nature of the Caulicle.—Probably some of the pupils will have called the caulicle the root. It is, however, of the nature of stem. The root grows only at the end, from a point just behind the tip; the stem elongates throughout its whole length. This can be shown by marking the stem and roots of a young seedling with ink. India ink must be used, as common ink injures the plants. Dip a needle in the ink and prick a row of spots at equal distances on a young root. Corn is very good for this purpose, but Morning-Glory or Bean is better for experiments on the stem. The plants should then be carefully watched and the changes in the relative distance of the spots noted. The experiment is very easily conducted with the seedlings growing on sponge, with their roots in the moist air of the tumbler, as before described.
Dr. Goodale says of this experiment,—"Let a young seedling of corn be grown on damp paper in the manner described in No. 1,[1] and when the longest root is a few centimetres long let it be marked very carefully by means of India ink, or purple ink, put on with a delicate camel's-hair pencil just one centimetre apart. Plants thus marked are to be kept under favorable conditions with respect to moisture and warmth, so that growth will be as rapid as possible. The marks on the older part of the root will not change their relative distance, but the mark at the tip will be carried away from the one next it, showing that the growth has taken place only at this point. Such experiments as the one described are perfectly practicable for all classes of pupils except the very youngest. How far the details of these experiments should be suggested to the pupils, or rather how far they should be left to work out the problem for themselves, is a question to be settled by the teacher in each case. The better plan generally is to bring the problem in a very clear form before the whole class, or before the whole school, and ask whether anybody can think of a way in which it can be solved; for instance, in this case how can it be found out whether roots grow only at their tip or throughout their whole length. If the way is thought out by even a single pupil the rest will be interested in seeing whether the plan will work successfully."
I have been more successful in pricking the roots than in marking them with a brush.
The caulicle can be proved by the manner of its growth to be of the nature of stem, not root. The main root grows from its naked end. Roots can also grow from the sides of the caulicle, as in Indian Corn. In this, it acts precisely as does the stem of a cutting. It can be prettily shown with the seedlings by breaking off a bean at the ground and putting the slip in water. It will throw out roots and the pupil will readily understand that the caulicle does the same thing.
Darwin has made very interesting experiments on the movements of seedlings. If the teacher wishes to repeat some of the experiments he will find the details very fully given in "The Power of Movement of Plants."[1] The pupils can observe in their growing seedlings some of the points mentioned and have already noticed a few in their answers. They have said that the caulicle was the part to grow first, and have spoken of the arched form of the young stem. Their attention should also be drawn to the root-hairs, which are well seen in Corn, Wheat, and Oats. They absorb the liquid food of the plants. A secondary office is to hold the seed firmly, so that the caulicle can enter the ground. This is shown in Red Clover, which may be sown on the surface of the ground. It puts out root-hairs, which attach themselves to the particles of sand and hold the seed. These hairs are treated more fully in the lessons on roots.
5. Leaves of Seedlings.—Coming now to the question as to the number of leaves at each joint of the stem, the Morning-Glory, Sunflower, and Bean will present no difficulty, but probably all the pupils will be puzzled by the Pea. The stipules, so large and leaf-like, look like two leaves, with a stem between, bearing other opposite leaves, and terminating in a tendril, while in the upper part it could not be told by a beginner which was the continuation of the main stem. For these reasons I left this out in the questions on the Pea, but it should be taken up in the class. How are we to tell what constitutes a single leaf? The answer to this question is that buds come in the axils of single leaves; that is, in the inner angle which the leaf makes with the stem. If no bud can be seen in the Pea, the experiment may be tried of cutting off the top of the seedling plant. Buds will be developed in the axils of the nearest leaves, and it will be shown that each is a compound leaf with two appendages at its base, called stipules, and with a tendril at its apex. Buds can be forced in the same way to grow from the axils of the lower scales, and even from those of the cotyledons, and the lesson may be again impressed that organs are capable of undergoing great modifications. The teacher may use his own judgment as to whether he will tell them that the tendril is a modified leaflet.
[Illustration: FIG. 9. 1. Grain of Indian Corn. 2. Vertical section, dividing the embryo, a, caulicle: b, cotyledon; c, plumule. 3. Vertical section, at right angles to the last.]
6. Monocotyledons.—These are more difficult. Perhaps it is not worth while to attempt to make the pupils see the embryo in Wheat and Oats. But the embryo of Indian Corn is larger and can be easily examined after long soaking. Removing the seed-covering, we find the greater part of the seed to be albumen. Closely applied to one side of this, so closely that it is difficult to separate it perfectly, is the single cotyledon. This completely surrounds the plumule and furnishes it with food from the albumen. There is a line down the middle, and, if we carefully bend back the edges of the cotyledon, it splits along this line, showing the plumule and caulicle within. The plumule consists of successive layers of rudimentary leaves, the outer enclosing the rest (Fig. 10, 1, c). The latter is the first leaf and remains undeveloped as a scaly sheath (Fig. 10, 2, c). In Wheat and Oats the cotyledon can be easily seen in the largest seedlings by pulling off the dry husk of the grain. The food will he seen to have been used up.
[Illustration: FIG. 10. 1. Germination of Indian corn. 2. Same more advanced. a, caulicle; c1, first leaf of the plumule, sheathing the rest; c2, second leaf; c3, third leaf of the plumule; d, roots.]
The series of Corn seedlings, at least, should be drawn as before and the parts marked, this time with their technical terms. The following questions should then be prepared.
CORN.
What are the parts of the seed?
Compare these parts with the Morning-Glory, Sunflower, Bean, and Pea.
Where is the food stored?
How many cotyledons have Corn, Wheat, and Oats?
How many have Bean, Pea, Morning-Glory, and Sunflower?
Compare the veins of the leaves of each class and see what difference you can find.
This will bring up the terms dicotyledon and monocotyledon. Di means two, mono means one. This difference in the veins, netted in the first class, parallel in the second, is characteristic of the classes. Pupils should have specimens of leaves to classify under these two heads. Flowering plants are divided first into these two classes, the Dicotyledons and the Monocotyledons.
If Pine-seeds can be planted, the polycotyledonous embryo can also be studied.
7. Food of seedlings.—The food of the Wheat seedling may be shown in fine flour. [1]"The flour is to be moistened in the hand and kneaded until it becomes a homogeneous mass. Upon this mass pour some pure water and wash out all the white powder until nothing is left except a viscid lump of gluten. This is the part of the crushed wheat-grains which very closely resembles in its composition the flesh of animals. The white powder washed away is nearly pure wheat-starch. Of course the other ingredients, such as the mineral matter and the like, might be referred to, but the starch at least should be shown. When the seed is placed in proper soil, or upon a support where it can receive moisture, and can get at the air and still be warm enough, a part of the starch changes into a sort of gum, like that on postage stamps, and finally becomes a kind of sugar. Upon this sirup the young seedling feeds until it has some good green leaves for work, and as we have seen in the case of some plants it has these very early."
The presence of starch can be shown by testing with a solution of iodine. Starch is turned blue by iodine and may thus be detected in flour, in seeds, in potatoes, etc.
After all this careful experimental work the subject may be studied in the text-book and recited, the recitation constituting a thorough review of the whole.
A charming description of the germination of a seed will be found in the Reader. V. The Birth of Picciola.
Gray's Lessons. Sect. II, 8-14. III. How Plants Grow. Sect. I, 22, 23. II.