Outlines of Lessons in Botany Part 8

What other tree that you have studied has this arrangement?

How old is your branch?

Where would you look to see if the flower-cl.u.s.ter had left any mark?

Why is it that several twigs grow near each other, and that then comes a s.p.a.ce without any branches?

What buds develop most frequently?

How does this affect the appearance of the tree?

What is a tree called when the trunk is lost in the branches?

BALM OF GILEAD (_Populus balsamifera, var. candicans_).

The buds are pointed: the terminal slightly angled, the axillary flattened against the stem.[1] Some of the axillary buds contain leaves and some flowers; the appearance of the leaf-buds and flower-buds being the same.

The scales of the bud are modified stipules. The terminal buds have about three pairs of the outer scales brown and leathery. The inner scales, as well as the leaves, are coated with resinous matter, which has a strong odor and a nauseous taste. The smaller outer scales have no corresponding leaf, and apparently are modified stipules of the leaves of the preceding year, but the larger ones have a leaf to each pair of scales. The outer and inner leaves are small, the middle ones larger. Comparing the branch, it will be seen that these leaves make the largest growth of internode.

The leaves are rolled towards the midrib on the upper face (_involute_).

There are about ten which are easily seen and counted, the inner ones being very small, with minute scales. The axillary buds have a short thick scale on the outer part of the bud, then about three pairs of large scales, each succeeding one enwrapping those within, the outer one brown and leathery. The scales of the flower-buds are somewhat gummy, but not nearly so much so as those of the leaf-buds. Within is the catkin. Each pistil, or stamen (they are on separate trees, _dioecious_) is in a little cup and covered by a scale, which is cut and fringed.

[Footnote 1: These buds cannot be satisfactorily examined in cross section, on account of the resin. The scales must be removed one by one, with a knife, with a complete disregard of the effect upon the hands.]

The leaf-scars are somewhat three-lobed on the young parts, with three dots, indicating the fibro-vascular bundles, which ran up into the leaf.

The scars are swollen, making the young branches exceedingly rough. In the older parts the scars become less noticeable. Strong young shoots, especially those which come up from the root, are strongly angled, with three ridges running up into each leaf-scar, making them almost club-shaped. There are often from twenty to thirty leaves in one year's growth, in such shoots, and all the leaves are not rudimentary in the bud.

The growth in this case is said to be _indefinite_. Usually in trees with scaly buds the plan of the whole year's growth is laid down in the bud, and the term _definite_ is applied. Branches, like the Rose, that go on growing all summer grow indefinitely.

The bud-scale scar is quite different from the other trees which we have examined. It is not composed of definite rings, but of leaf-scars with long ridges running from each side of them, showing the scales to be modified stipules. The leaf-scars have become somewhat separated by the growth of the internodes. In the Beech, there are eight, or more, pairs of scales with no leaves, so that the internodes do not develop, and a ring is left on the branch.

The flower-cl.u.s.ter leaves a concave, semicircular scar, in the leaf-axil.

[Ill.u.s.tration: FIG. 17.--Balm-of-Gilead. 1. Branch in winter state: _a_, leaf-scar; _b_, bud-scar. 2. Branch, with leaf-buds expanded. 3. Branch, with catkin appearing from the bud.]

The terminal buds are the strongest and not very many axillary buds develop, so that the tree has not fine spray.

The leaf-arrangement is alternate, on the 2/5 plan. Phyllotaxy is not yet to be taken up, but the pupils should be shown the different angles of the branching of the twigs, and told to compare them with Beech and Elm.

QUESTIONS ON THE BALM OF GILEAD.

In which buds are the flower-cl.u.s.ters?

Are there flowers and leaves in the same buds?

What are the scales of the bud?

How are the leaves folded in the bud?

How do the axillary and terminal buds differ?

What are the dots on the leaf-scars?

Why is there no distinct band of rings as in Beech?

How old is your branch?

Where do you look for flower-cl.u.s.ter scars?

Which buds are the strongest?

How does this affect the appearance of the tree?

What makes the ends of the branches so rough?

Compare the arrangement of the twigs and branches with Beech and Elm, with Horsechestnut and Lilac.

TULIP-TREE (_Liriodendron Tulipifera_).

The buds are small, flat, and rounded at the apex. They are sheathed by scales, each leaf being covered by a pair, whose edges cohere. The outer pair are brown and are the stipules of the last leaf of the preceding year. The leaves are conduplicate, as in Magnolia, and have the blade bent inwards on the petiole (_inflexed_). Their shape is very clearly to be seen, and no bud is more interesting in the closeness of its packing.

Axillary buds are often found within. The flowers grow high upon the trees and towards the ends of the branches.

The leaf-scars are round with many dots. The scar of the stipules is a continuous line around the stem, as in Magnolia.

CHERRY _(Prunus Cerasus_).

The leaf-buds are terminal, or in the axils of the upper leaves of the preceding year; the flower buds are axillary. There is but one bud in each axil, and usually two or three flowers in each bud, but the leaves on the twigs are crowded and the flowers therefore appear in cl.u.s.ters. The blossom-buds are larger and more rounded than the leaf-buds.

The buds of the tree develop very easily in the house, and as they are so small they can be better studied in watching them come out, than by attempting to dissect them, unless the scholars are sufficiently advanced to use the microscope easily. It is always bad for a pupil to attempt to describe what he sees but imperfectly. He will be sure to jump at any conclusions which he thinks ought to be correct.

The leaf-scars are semicircular, small and swollen.

The bud-rings are plain. The twigs make a very small growth in a season, so that the leaf-scars and rings make them exceedingly rough.

The flower-cl.u.s.ter scars are small circles, with a dot in the centre, in the leaf-axils. The flowers come before the leaves.

The leaf-arrangement is alternate on the 2/5 plan. The pupils may compare the branching with that of their other specimens.

RED MAPLE (_Acer rubrum_).

This is a good specimen for the study of accessory buds. There is usually a bud in the axil of each lower scale of the axillary buds, making three side by side. We have already noticed this as occurring sometimes in Lilac. It is habitually the case with the Red Maple. The middle bud, which is smaller and develops later, is a leaf-bud. The others are flower-buds.

The leaf-scars are small, with three dots on each scar. The rings are very plain. The flower-cl.u.s.ter leaves a round scar in the leaf-axil, as in Cherry.

The leaves are opposite and the tree branches freely. The twigs seem to be found just below the bud-rings, as the upper leaf-buds usually develop best and the lower buds are single, containing flowers only.

NORWAY SPRUCE (_Picea excelsa_).