Outlines of Lessons in Botany Part 3

They may also be divided into those with and without the plumule.

_Without Plumule_. _With Plumule_.

Flax. Maple. Sunflower. Acorn. Horsechestnut.

Four-o'clock. Almond. Bean. Pea.

Morning-Glory. Squash. Nasturtium.

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 Air_. _In the Ground_.

Bean. Almond. Squash. Acorn. Horsechestnut.

Pea. Nasturtium.

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 ill.u.s.trations 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 p.r.i.c.k 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 cla.s.ses 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 cla.s.s, 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."

[Footnote 1: Concerning a Few Common Plants, page 25.]

I have been more successful in p.r.i.c.king 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.

[Footnote 1: The Power of Movement in Plants. By Charles Darwin. London.

John Murray, 1880.]

[Footnote 1: Reader in Botany. IV. Movements of Seedlings.]

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 cla.s.s. How are we to tell what const.i.tutes 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.

[Ill.u.s.tration: 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 alb.u.men. 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 alb.u.men. 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.

[Ill.u.s.tration: FIG. 10. 1. Germination of Indian corn. 2. Same more advanced. _a_, caulicle; _c_1, first leaf of the plumule, sheathing the rest; _c_2, second leaf; _c_3, 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 cla.s.s 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 cla.s.s, parallel in the second, is characteristic of the cla.s.ses. Pupils should have specimens of leaves to cla.s.sify under these two heads.

Flowering plants are divided first into these two cla.s.ses, 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 h.o.m.ogeneous ma.s.s. Upon this ma.s.s 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."

[Footnote 1: Concerning a Few Common Plants, page 18.]

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 const.i.tuting 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.

III

ROOTS.

This subject can be treated more conveniently while the young seedlings are still growing, because their roots are very suitable for study. It seems best, therefore, to take it up before examining the buds.

1. _Study of the Roots of Seedlings_.--One or two of the seedlings should be broken off and the slips put into a gla.s.s of water. They will be studied later. Bean and Sunflower are the best for the purpose.