found, which will
afford excellent illustrations (Fig. 21). The Marguerite and Tobacco, both
easily grown in the house, are on the 3/8 plan. The latter shows the eight
ranks most plainly in the rosette of its lower leaves. The distribution is
often brought about by differences in the lengths of the petioles, as in
a Horsechestnut branch (Fig. 22) where the lower, larger leaves stand
out further from the branch than the upper ones; or by a twist in the
petioles, so that the upper faces of the leaves are turned up to the
light, as in Beech (Fig. 23). If it is springtime when the lessons are
given, endless adaptations can be found.

[Footnote 1: Reader in Botany. IX. Leaf-Arrangement.]

[Illustration: FIG. 21. Branch of Geranium, viewed from above.]

[Illustration: FIG. 22.]

[Illustration: FIG. 23.]

_Gray's First Lessons_. Sect. IV. VII, sec. 4. _How Plants Grow_. Chap. I,
51-62; I, 153.

V.

STEMS.

The stem, as the scholars have already learned, is the axis of the plant.
The leaves are produced at certain definite points called nodes, and the
portions of stem between these points are internodes. The internode,
node, and leaf make a single plant-part, and the plant is made up of a
succession of such parts.

The stem, as well as the root and leaves, may bear plant-hairs. The
accepted theory of plant structure assumes that these four parts, root,
stem, leaves, and plant-hairs, are the only members of a flowering plant,
and that all other forms, as flowers, tendrils, etc., are modified from
these. While this idea is at the foundation of all our teaching, causing
us to lead the pupil to recognize as modified leaves the cotyledons of a
seedling and the scales of a bud, it is difficult to state it directly
so as to be understood, except by mature minds. I have been frequently
surprised at the failure of even bright and advanced pupils to grasp this
idea, and believe it is better to let them first imbibe it unconsciously
in their study. Whenever their minds are ready for it, it will be readily
understood. The chief difficulty is that they imagine that there is a
direct metamorphosis of a leaf to a petal or a stamen.

Briefly, the theory is this: the beginnings of leaf, petal, tendril, etc.,
are the same. At an early stage of their growth it is impossible to tell
what they are to become. They develop into the organ needed for the
particular work required of them to do. The organ, that under other
circumstan