Outlines of Lessons in Botany Part 6

In some parts of the country the Horsechestnut is not so commonly planted as in New England. In the southern states the Magnolia may be used in its stead, but it is not nearly so simple an example of the main points to be observed.[1]

[Footnote 1: Reader in Botany. VII. Trees in Winter.]

MAGNOLIA UMBRELLA.

The bud may be examined by removing the scales with a knife, as in Horsechestnut, and also by cutting sections. The outer scales enfold the whole bud, and each succeeding pair cover all within. They are joined, and it is frequently difficult to tell where the suture is, though it can generally be traced at the apex of the bud. On the back is a thick stalk, which is the base of the leaf-stalk. Remove the scales by cutting carefully through a single pair, opposite the leaf-stalk, and peeling them off. The scales are modified stipules, instead of leaf-stalks, as in Horsechestnut. The outer pair are brown and thick, the inner green, and becoming more delicate and crumpled as we proceed toward the centre of the bud. The leaves begin with the second or third pair of scales. The first one or two are imperfect, being small, brown, and dry. The leaves grow larger towards the centre of the bud. They are covered with short, silky hairs, and are folded lengthwise, with the inner surface within (_conduplicate_). In the specimens I have examined I do not see much difference in size between the buds with flowers and those without. In every bud examined which contained a flower, there was an axillary bud in the axil of the last, or next to the last, leaf. This bud is to continue the interrupted branch in the same way as in Horsechestnut.

There are from six to ten good leaves, in the buds that I have seen. Those without flowers contain more leaves, as in Horsechestnut. In the centre of these buds the leaves are small and undeveloped. The flower is very easy to examine, the floral envelopes, stamens and pistils, being plainly discernible. The bud may also be studied in cross-section. This shows the whole arrangement. The plan is not so simple as in Horsechestnut, where the leaves are opposite. The subject of leaf-arrangement should be pa.s.sed over until phyllotaxy is taken up.

The scars on the stem differ from Horsechestnut in having no distinct bands of rings. The scales, being stipules, leave a line on each side of the leaf-scar, and these are separated by the growth of the internodes.

In the Beech, the scales are also stipules; but, whereas in the Magnolia there are only one or two abortive leaves, in the Beech there are eight or nine pairs of stipules without any leaves at all. The rings thus become separated in Magnolia, while in the Beech the first internodes are not developed, leaving a distinct band of rings, to mark the season's growth.

The Magnolia is therefore less desirable to begin upon. The branches are swollen at the beginning of a new growth, and have a number of leaf-scars crowded closely together. The leaf-scars are roundish, the lower line more curved. They have many dots on them. From each leaf-scar runs an irregular line around the stem. This has been left by the stipules.

The flower-scar is on the summit of the axis, and often apparently in the axil of a branch, as in Horsechestnut. Sometimes the nearest axillary bud is developed; sometimes there are two, when the branch forks. The axillary buds seldom grow unless the terminal bud is interrupted. The tree therefore has no fine spray.

LILAC _(Syringa vulgaris_).

Ask the scholars to write a description of their branches and to compare them with Horsechestnut. These papers should be prepared before coming into the cla.s.s, as before.

The buds are four-sided. The scales and leaves are opposite, as in Horsechestnut. The outer pair sometimes have buds in their axils. Remove the scales one by one with a knife, or better, with a stout needle. The scales gradually become thinner as we proceed, and pa.s.s into leaves, so that we cannot tell where the scales end and leaves begin. After about six pairs are removed, we come, in the larger buds, to leaves with axillary flower-cl.u.s.ters. The leaves grow smaller and the flower-cl.u.s.ters larger till we come to the centre, where the axis is terminated by a flower-cl.u.s.ter. There is a great difference in the buds on different bushes and on shoots of the same bush, some being large, green, and easy to examine, others small, hard, and dark-colored. It is better, of course, to select as soft and large buds as possible for examination.

[Ill.u.s.tration: FIG. 14.--Lilac. I. Branch in winter state: _a_, leaf-scar; _b_, bud-scar (reduced). 2. Same, less reduced. 3. Branch, with leaf-buds expanded. 4. Series in a single bud, showing the gradual transition from scales to leaves.]

That the scales are modified leaves is plainly shown by the gradual transition they undergo, and also by the fact that buds are developed in their axils. If any of these can be shown to the pupils, remind them of the experiment where the top of a seedling Pea was cut off and buds forced to develop in the axils of the lower scales.[1] The transition from scales to leaves can be well studied by bringing branches into the house, where they will develop in water, and towards spring may even be made to blossom. Cherry, Apple, Forsythia, and other blossoming trees and shrubs can be thus forced to bloom. Place the branches in hot water, and cut off a little of their ends under water. If the water is changed every day, and the gla.s.s kept near the register or stove, they will blossom out very quickly. These expanded shoots may be compared with the buds. The number of leaves in the bud varies.

[Footnote 1: See p. 31.]

The leaf-scars of Lilac are horseshoe-shaped and somewhat swollen. It can often be plainly seen that the outer tissue of the stem runs up into the scar. It looks as if there were a layer of bark, ending with the scar, fastened over each side of the stem. These apparent layers alternate as well as the scars. The epidermis, or skin of the leaves, is in fact always continuous with that of the stem. There are no dots on the leaf-scars.

The rings are not nearly so noticeable as in Horsechestnut, but they can be counted for some years back.

The flower-cl.u.s.ter can often be traced by a dried bit of stem remaining on the branch.

The terminal bud in the Lilac does not usually develop, and the two uppermost axillary buds take its place, giving to the shrub the forked character of its branching. In all these bud studies, the pupil should finish by showing how the arrangement of the buds determines the growth of the branches.

QUESTIONS ON THE LILAC.

How do the scales differ from those of Horsechestnut?

How many scales and leaves are there?

How are they arranged?

Where does the flower-cl.u.s.ter come in the bud?

Do all the buds contain flower-cl.u.s.ters?

How does the arrangement of leaves and flower-cl.u.s.ters differ from that of Horsechestnut?

How old is your branch?

Which buds develop most frequently?

How does this affect the appearance of the shrub?

COPPER BEECH (_f.a.gus sylvatica, var. purpurea_).

The buds are long and tapering, the scales thin and scarious, the outer naked, the inner with long, silky hairs. Remove the scales one by one, as in Lilac. The outer four or six pairs are so minute that the arrangement is not very clear, but as we proceed we perceive that the scales are in alternate pairs, as in Horsechestnut; that is, that two scales are exactly on the same plane. But we have learned in the Lilac that the scales are modified leaves, and follow the leaf-arrangement of the species. The Beech is alternate-leaved, and we should therefore expect the scales to alternate. The explanation is found as we go on removing the scales. At the eighth or ninth pair we come upon a tiny, silky leaf, directly between the pair of scales, and, removing these, another larger leaf, opposite the first but higher up on the rudimentary stem, and so on, with the rest of the bud. There are five or more leaves, each placed between a pair of scales. Our knowledge of the parts of a leaf shows us at once that the scales must be modified stipules, and that therefore they must be in pairs.[1] Other examples of scales h.o.m.ologous with stipules are the American Elm, Tulip-tree, Poplar and Magnolia. The leaves are plaited on the veins and covered with long, silky hairs. The venation is very distinct. The outer leaves are smaller and, on examining the branch, it will be seen that their internodes do not make so large a growth as the leaves in the centre of the bud.

[Footnote 1: See the stipules of the Pea, p. 31.]

[Ill.u.s.tration: FIG. 15.--Copper Beech. 1. Branch in winter state: _a_, leaf-scar; _b_, bud-scar. 2. Branch, with leaf-buds expanding, showing the plicate folding of the leaves.]

The leaf-scars are small, soon becoming merely ridges running half round the stem.

The bud-rings are very plain and easily counted. For this reason, and because it branches freely, it is a good tree for measurements of growth, as is seen in the following tables. Nos. 1, 2, 3 and 4: were made by a cla.s.s of girls, from fourteen to sixteen, from a tree on my lawn. No. 5 was made by a pupil, whom I taught by correspondence, from a tree of the same species in another town. No. 6 was made by myself from my own tree.

The measurements of the first four tables were somewhat revised by me, as they were not perfectly accurate. The pupils should always be cautioned to measure from the beginning of one set of rings to the beginning of the next.[1]

[Footnote 1: Care must be taken to select branches well exposed to the light. Of course there are many circ.u.mstances that may aid or hinder the growth of any particular branch.]

NO. 1.

YEARS. GROWTH OF 1ST BRANCH. 2nd BRANCH. 3RD BRANCH 4TH BRANCH.

MAIN AXIS.

---------------------------------------------------------------- in.

'79 8-1/2 -- -- -- -- '80 4-1/2 2 1-7/8 -- -- '81 3-1/2 1-1/8 2-5/8 -- -- '82 6 5/8 4-1/4 5-7/8 -- '83 7-3/8 3-3/8 5-1/4 4 5-3/4 '84 2 1/2 3/4 3/8 5-3/8 '85 5/8 1/4 3/8 1/2 1 '86 5-5/8 7/8 4-3/8 3-1/8 5

NO. 2.

YEARS. GROWTH of 1ST 2nd 3RD 4TH 5TH MAIN AXIS. BRANCH BRANCH BRANCH BRANCH BRANCH ---------------------------------------------------------------- in.

'79 8 -- -- -- -- -- -- '80 3-1/2 5-1/4 5-1/2 5-5/8 -- -- -- '81 4-3/4 3/4 1/2 2-1/2 2 -- -- '82 5-3/4 7/8 2 3/4 3/8 1/2 -- '83 5-1/4 4-3/4 5-1/2 4 3-1/4 2-3/8 1-3/4 -- '84 1/2 1 3/4 3/8 1 3/4 1 3/8 '85 2-3/4 1-3/4 4-3/8 3/4 3/4 2-1/8 3-1/4 1-1/4 '86 7-1/2 5-1/2 6-3/4 3 3 4-1/2 3-1/8 5

NO. 3.

YEARS. GROWTH of 1ST 2nd 3RD 4TH 5TH MAIN AXIS. BRANCH BRANCH BRANCH BRANCH BRANCH ----------------------------------------------------- in.

'80 8-1/4 -- -- -- -- -- '81 4-1/2 3-1/2 3-3/4 -- -- -- '82 5-1/2 3/4 1-1/2 1 -- -- '83 3-1/4 3-3/4 4-1/2 3/4 2 1-1/4 '84 5-1/2 1/2 3/4 1 1/2 3 '85 1/2 1-3/4 1/2 3/8 1 1/2 '86 4-1/4 3-3/8 2-3/8 1-1/4 2-1/4 1-1/2

NO. 4.

YEARS GROWTH 1ST 2nd 3RD 4TH of MAIN BRANCH BRANCH BRANCH BRANCH AXIS ----------------------------------------- in.

'81 7-3/4 -- -- -- -- '82 8-3/4 6 6 -- -- '83 6-3/4 5-1/4 4 4-3/4 5-1/2 '84 4-1/2 5/8 1-5/8 2-1/4 3-1/4 '85 2 5/8 3/16 2 3/4 '86 10-3/4 1-3/4 1/4 7-1/4 3-1/2