of monocotyledons
have stems without distinction of wood, bark and pith; the netted-veined
leaves of dicotyledons have exogenous stems.

Dicotyledons have bark, wood, and pith, and grow by producing a new ring
of wood outside the old. They also increase by the growth of the woody
bundles of the leaves, which mingle with those of the stem.[1] Twist off
the leaf-stalk of any leaf, and trace the bundles into the stem.

[Footnote 1: See note, p. 127, Physiological Botany.]

Monocotyledons have no layer which has the power of producing new wood,
and their growth takes place entirely from the intercalation of new
bundles, which originate at the bases of the leaves. The lower part of a
stem of a Palm, for instance, does not increase in size after it has lost
its crown of leaves. This is carried up gradually. The upper part of the
stem is a cone, having fronds, and below this cone the stem does not
increase in diameter. The word _endogenous_, inside-growing, is not,
therefore, a correct one to describe the growth of most monocotyledons,
for the growth takes place where the leaves originate, near the exterior
of the stem.

_Gray's First Lessons_. Sect. VI. Sect, XVI, sec. 1, 401-13. sec. 3.
sec. 6, 465-74.

_How Plants Grow_. Chap. 1, 82, 90-118.

VI.

LEAVES.

We have studied leaves as cotyledons, bud-scales, etc., but when we speak
of _leaves_, we do not think of these adapted forms, but of the green
foliage of the plant.

1. _Forms and Structure_.--Provide the pupils with a number of green
leaves, illustrating simple and compound, pinnate and palmate, sessile and
petioled leaves. They must first decide the question, _What are the parts
of a leaf_? All the specimens have a green _blade_ which, in ordinary
speech, we call the leaf. Some have a stalk, or _petiole_, others are
joined directly to the stem. In some of them, as a rose-leaf, for
instance, there are two appendages at the base of the petiole, called
_stipules_. These three parts are all that any leaf has, and a leaf that
has them all is complete.

Let us examine the blade. Those leaves which have the blade in one
piece are called _simple_; those with the blade in separate pieces are
_compound_. We have already answered the question, _What constitutes a
single leaf_?[1] Let the pupils repeat the experiment of cutting off the
top of a seedling Pea, if it is not already clear in their minds, and find
buds in the leaf-axils of other plants.[2]

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