and flattened,
sometimes into thin margins, sometimes into a sheath which embraces the
stem at the point of attachment.

[Illustration: Fig. 177. Leaf of Red Clover: _st_, stipules, adhering to
the base of _p_, the petiole; _b_, blade of three leaflets.]

[Illustration: Fig. 178. Part of stem and leaf of Prince's-Feather
(Polygonum orientale) with the united sheathing stipules forming a
sheath or _ocrea_.]

[Illustration: Fig. 179. Terminal winter bud of Magnolia Umbrella,
natural size. 180. Outermost bud-scale (pair of stipules) detached.]

176. =Stipules= are such appendages, either wholly or partly separated
from the petiole. When quite separate they are said to be _free_, as in
Fig. 112. When attached to the base of the petiole, as in the Rose and
in Clover (Fig. 177), they are _adnate_. When the two stipules unite
and sheathe the stem above the insertion, as in Polygonum (Fig. 178),
this sheath is called an _Ocrea_ from its likeness to a greave or
leggin.

177. In Grasses, when the sheathing base of the leaf may answer to
petiole, the summit of the sheath commonly projects as a thin and short
membrane, like an ocrea: this is called a LIGULA or LIGULE.

178. When stipules are green and leaf-like they act as so much foliage.
In the Pea they make up no small part of the actual foliage. In a
related plant (Lathyrus Aphaca, Fig. 173), they make the whole of it,
the remainder of the leaf being tendril.

179. In many trees the stipules are the bud-scales, as in the Beech, and
very conspicuously in the Fig-tree, Tulip-tree, and Magnolia (Fig. 179).
These fall off as the leaves unfold.

180. The stipules are spines or prickles in Locust and several other
Leguminous trees and shrubs; they are tendrils in Smilax or Greenbrier.

Sec. 4. THE ARRANGEMENT OF LEAVES.

181. =Phyllotaxy=, meaning leaf-arrangement, is the study of the
position of leaves, or parts answering to leaves, upon the stem.

[Illustration: Fig. 181. Alternate leaves, in Linden, Lime-tree, or
Basswood.]

[Illustration: Fig. 182. Opposite leaves, in Red Maple.]

182. The technical name for the attachment of leaves to the stem is the
_insertion_. Leaves (as already noticed, 54) are _inserted_ in three
modes. They are

_Alternate_ (Fig. 181), that is, one after another, or in other words,
with only a single leaf to each node;

_Opposite_ (Fig. 182), when there is a pair to each node, the two
leaves in this case being always on opposite sides