Outlines of Lessons in Botany, Part I; from Seed to Leaf / For the Use of Teachers, or Mothers Studying with Their Children

by Jane Newell Moore

We will begin with the study of a branch of Horsechestnut.[1] The pupils should examine and describe their specimens before discussing them in the class-room. They will need some directions and hints, however, to enable them to work to any advantage. Tell them to open both large and small buds. It is not advisable to study the Horsechestnut bud by cutting sections, as the wool is so dense that the arrangement cannot be seen in this way. The scales should be removed with a knife, one by one, and the number, texture, etc., noted. The leaves and flower-cluster will remain uncovered and will be easy to examine. The gum may be first removed by pressing the bud in a bit of paper. The scholars should study carefully the markings on the stem, in order to explain, if possible, what has caused them. The best way to make clear the meaning of the scars is to show them the relation of the bud to the branch. They must define a bud. Ask them what the bud would have become the next season, if it had been allowed to develop. It would have been a branch, or a part of one. A bud, then, is an undeveloped branch. They can always work out this definition for themselves. Conversely, a branch is a developed bud, or series of buds, and every mark on the branch must correspond to something in the bud. Let them examine the specimens with this idea clearly before their minds. The lesson to prepare should be to write out all they can observe and to make careful drawings of their specimens. Ask them to find a way, if possible, to tell the age of the branch.

[Footnote 1: The pupils should cut their names on their branches and keep them. They will need them constantly for comparison and reference.]

At the recitation, the papers can be read and the points mentioned thoroughly discussed. This will take two lesson-hours, probably, and the drawing may be left, if desired, as the exercise to prepare for the second recitation.

[1]The buds of Horsechestnut contain the plan of the whole growth of the next season. They are scaly and covered, especially towards the apex, with a sticky varnish. The scales are opposite, like the leaves. The outer pairs are wholly brown and leathery, the succeeding ones tipped with brown, wherever exposed, so that the whole bud is covered with a thick coat. The inner scales are green and delicate, and somewhat woolly, especially along the lapping edges. There are about seven pairs of scales. The larger terminal buds have a flower-cluster in the centre, and generally two pairs of leaves; the small buds contain leaves alone, two or three pairs of them. The leaves are densely covered with white wool, to protect them from the sudden changes of winter. The use of the gum is to ward off moisture. The flower-cluster is woolly also.

[Footnote 1: All descriptions are made from specimens examined by me. Other specimens may differ in some points. Plants vary in different situations and localities.]

The scars on the stem are of three kinds, leaf, bud-scale, and flower-cluster scars. The pupils should notice that the buds are always just above the large triangular scars. If they are still in doubt as to the cause of these marks, show them some house-plant with well-developed buds in the axils of the leaves, and ask them to compare the position of these buds with their branches. The buds that spring from the inner angle of the leaf with the stem are axillary buds; those that crown the stems are terminal. Since a bud is an undeveloped branch, terminal buds carry, on the axis which they crown, axillary buds give rise to side-shoots. The leaf-scars show the leaf-arrangement and the number of leaves each year. The leaves are opposite and each pair stands over the intervals of the pair below. The same is observed to be true of the scales and leaves of the bud.[1] All these points should be brought out by the actual observation of the specimens by the pupils, with only such hints from the teacher as may be needed to direct their attention aright. The dots on the leaf-scar are the ends of woody bundles (fibro-vascular bundles) which, in autumn, separated from the leaf. By counting these we can tell how many leaflets there were in the leaf, three, five, seven, nine, or occasionally six or eight.

[Footnote 1: Bud-scales are modified leaves and their arrangement is therefore the same as the leaves. This is not mentioned in the study of the Horsechestnut bud, because it cannot be proved to the pupils, but the transition is explained in connection with Lilac, where it may be clearly seen. The scales of the bud of Horsechestnut are considered to be homologous with petioles, by analogy with other members of the same family. In the Sweet Buckeye a series can be made, exhibiting the gradual change from a scale to a compound leaf. See the Botanical Text-Book, Part I, Structural Botany. By Asa Gray. Ivison, Blakeman, Taylor and Co., New York, 1879. Plate 233, p. 116.]

[Illustration: FIG. 13.—Horsechestnut. I. Branch in winter state: a, leaf-scars; b, bud-scars; c, flower-scars. 2. An expanding leaf-bud. 3. Same, more advanced.]

The Bud Scale-Scars. These are rings left by the scales of the bud and may be seen in many branches. They are well seen in Horsechestnut. If the pupils have failed to observe that these rings show the position of former buds and mark the growth of successive years, this point must be brought out by skilful questioning. There is a difference in the color of the more recent shoots, and a pupil, when asked how much of his branch grew the preceding season, will be able to answer by observing the change in color. Make him see that this change corresponds with the rings, and he will understand how to tell every year's growth. Then ask what would make the rings in a branch produced from one of his buds, and he can hardly fail to see that the scales would make them. When the scholars understand that the rings mark the year's growth, they can count them and ascertain the age of each branch. The same should be done with each side-shoot. Usually the numbers will be found to agree; that is, all the buds will have the same number of rings between them and the cut end of the branch, but occasionally a bud will remain latent for one or several seasons and then begin its growth, in which case the numbers will not agree; the difference will be the number of years it remained latent. There are always many buds that are not developed. "The undeveloped buds do not necessarily perish, but are ready to be called into action in case the others are checked. When the stronger buds are destroyed, some that would else remain dormant develop in their stead, incited by the abundance of nourishment which the former would have monopolized. In this manner our trees are soon reclothed with verdure, after their tender foliage and branches have been killed by a late vernal frost, or consumed by insects. And buds which have remained latent for several years occasionally shoot forth into branches from the sides of old stems, especially in certain trees."[1]