en when present, they frequently fall
off as soon as the leaves expand; sometimes they are conspicuous. Most
Willows show the stipules on the young luxuriant growths.

[Illustration: Fig. 7.]

VEINING.--The leaves of most trees have a distinct framework, the
central line of which is called a _midrib_; sometimes the leaf has
several other lines about as thick as the midrib, which are called
_ribs_; the lines next in size, including all that are especially
distinct, are called _veins_, the most minute ones being called
_veinlets_ (Fig. 8).

[Illustration: Fig. 8.]

KINDS.--Leaves are _simple_ when they have but one blade; [Illustration]
_compound_ when they have more than one. Compound leaves are _palmate_
when all the blades come from one point, as in the Horse-chestnut;
[Illustration] _pinnate_ when they are arranged along the sides, as in
the Hickory. Pinnate leaves are of two kinds: _odd-pinnate_,
[Illustration] when there is an odd leaflet at the end, as in the Ash,
and _abruptly pinnate_ [Illustration] when there is no end leaflet.

Many trees have the leaves _twice pinnate_; they are either _twice
odd-pinnate_ [Illustration] or _twice abruptly pinnate_. [Illustration]
The separate blades of a compound leaf are called _leaflets_. Leaves or
leaflets are _sessile_ when they have no stems, and _petiolate_ when
they have stems.

When there are several ribs starting together from the base of a blade,
it is said to be _radiate-veined_ or _palmate-veined_.[Illustration]
When the great veins all branch from the midrib, the leaf is
_feather-veined_ or _pinnate-veined_. [Illustration] If these veins are
straight, distinct, and regularly placed, the leaf is said to be
_straight-veined_. The Chestnut is [Illustration] a good example. Leaves
having veinlets joining each other like a net are said to be
_netted-veined_. All the trees with broad leaves in the northern United
States, with one exception, have netted-veined foliage. A leaf having
its veinlets parallel to one another is said to be _parallel-veined_ or
_-nerved_. [Illustration] The Ginkgo-tree, the Indian Corn, and the
Calla Lily have parallel-veined leaves. The narrow leaves of the
cone-bearing trees are also parallel-veined.

FORMS.--Leaves can readily be divided into the three following groups
with regard to their general outline:

1. _Broadest at the middle._ _Orbicular_, [Illustration] about as broad
as long and rounded. _Oval_, [Illustration] about