Fig. 177. Leaf of Red Clover: st, stipules, adhering to the base of p, the petiole; b, blade of three leaflets.
Fig. 178. Part of stem and leaf of Prince's-Feather (Polygonum orientale) with the united sheathing stipules forming a sheath or ocrea.
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.
[§ 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.