247. Stipules are certain leaf-like expansions, always in pairs, situated one on each side of the petiole near the base. They do not occur in every plant, but are pretty uniformly present in each species of the same natural order. In substance and color they usually resemble the leaf, sometimes they are colored like the stem, often they are membranous. and colorless. In the palmetto its substance is a coarse net-work re-sembling canvass.
100, Rose leaf, odd-pinnate, with adnate stipules. 101, Violet, (V. tricolor), with simple leaf
( l), and free compound stipules.
248. Stipules are often adnate or adherent to the petiole, as in the rose; more generally they are free, as in the pea and pansy. In these cases and others they act the part of leaves; again they are very small and inconspicuous.
249. An ochrea is a membranous sheath inclosing the stem from the node upwards, as in the knot-grass family (Polygonaceae). It is formed of the two stipules cohering by their two margins. In case the two stipules cohere by their outer margin only, a double stipule is formed opposite to the leaf, as in the button-wood. If they cohere by their inner margin, the double stipule appears in the leaf axil, as in the pond-weed (Potamogeton).
. 250. Inter-petiolar stipules occur in a few opposite leaved tribes, as the Galium tribe. Here we find them as mere bristles in Diodia while in Galium they look like the leaves, forming whorls. Such whorls, if complete, will be apparently 6-leaved, consisting of two true leaves and four stipules. But the adjacent 9tipules are often united, and the whorl becomes 4-leaved.
102, Leaf of Conloselinum. tripinnate, with sheathing petiole. 103, Leaf of Polygonum Penn-sylvamcum, with its (o) ochrea. 104, Culm of grass, with joint (j), leaf (l) ligule (8)• 105, Leaf of pear-tree, with slender stipules.
251. The Ligule of grasses is generally regarded as a double axillary stipule. The leaflets of compound leaves are sometimes furnished with little stipules, called stipels.
252. Stipules are often fugacious, existing as scales in the bud, and falling when the leaves expand, or soon after, as in the Magnolia and tulip-tree.