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 passed
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 class, 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 pass 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-clusters. The leaves grow smaller and the flower-clusters
larger till we come to the centre, where the axis is terminated by a
flower-cluster. 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.
[Illustration: 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 glass 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-cluster 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.