CHAPTER VI

ON THE FORMS OF STIPULES

THOUGH stipules do not show such endless differences in form as is the case with leaves, nevertheless they present an immense variety.

They may be orbicular, as in Tropaeolum ciliatum (fig. 312); semi-orbicular, as in Guaiacum officinale (fig. 30); ovate, as in Passiflora racemosa, Hop (fig. 47), and Abutilon megapotamicum; obovate, as in Bucklandia (fig. 190); oblong, as in Leea (fig. 188) and Alder (fig. 145); elliptic, as in Hazel Nut (fig. 212); spathulate; lanceolate, as in Paronychia serpyllifolia and Pyrus japonica; linear, as in Disanthus (Hamamelideœ) and Ficus infectoria; filiform, as in Turkey Oak (Quercus Cerris); subulate, as in Mahonia and several species of Helianthemum; sagittate, as in Lathyrus pratensis (fig. 299) and L. maritimus; semi-sagittate, as in Lathyrus latifolius (fig. 300) and L. grandiflorus; reniform, as in Vallea (Sterculiacea); triangular, as in Ceanothus rigidus ; boat-shaped, as in Populus nigra (fig. 192); palmately lobed, as in Croton; laciniate, as in Trigonella laciniata ; pinnatifid, as in several species of Croton, Medicago and

Melilotus; pinnatipartite, as in Viola tricolor (fig. 27), Passiflora pinnatistipula, and Pomaria glandulosa; or palmatipartite, as in Althea rosea, A. ficifolia, Pterospermum acerifolium, &c.

In texture they may be foliaceous, as in the Heartsease; membranous, when thin, flexible, and almost transparent; scarious, when dry and coriaceous, as generally in the Beech and Hornbeam; spinous, as in Robinia (fig. 34); cirrhose, when produced into tendrils, as in Smilax.

In many cases the stipules are very small, sometimes quite minute, as in Hymenanthera (fig. 28), a plant belonging to the Violet family. The Holly is described in Bentham and Hooker's Genera Plantarum' as exstipulate, but (fig. 29) there are minute black points at the base of the leaves, which appear to represent stipules. In others they are very large, as in the common Pea (Pisum sativum) (fig. 26), Lathyrus maritimus (fig. 296), and Bucklandia (fig. 190).

Many plants have stipules of different forms.

The stipules covering winter-buds are often different in form from those of the subsequent leaves (see, for instance, figs. 215-235).

Where stipules serve as bud-scales there is generally a series of different forms, from those of the outer scale to those of the ordinary leaf.

In the Thorn (Crataegus Oxyacantha) (fig. 286) the stipules on the leaves of the short lateral spurs and those

M

at the very base of the elongating shoots are minute and toothlike, or subulate, soon becoming brown and falling early. Those on the upper part of the elongating shoots

St

St

sr

FIG. 286.-LEAVES OF HAWTHORN.

vary from unilateral, falcate, serrated, small but foliaceous organs, to large, half-cordate, simply or doubly serrate, shortly stalked, foliaceous, much-reticulated

organs, with the principal nerves radiating from the base of the lamina and passing into the principal teeth. Thus there are at least three distinct types of stipules.

These differences are probably connected with the differences in the shoots. These may be described as of two kinds, namely, those which develop into more or less lengthy, leafy shoots, which go to increase the height and breadth of the tree, and those which form short lateral spurs. The latter are very numerous, forming dense rosettes of leaves, and produce clusters of flowers in profusion in adult bushes and trees. Owing to the crowded state of their leaves, the bases of their petioles occupy the whole, or very nearly the whole, of the surface of the short axis, thus leaving little or no space for stipules. The lower or outer leaves are very small, and entire, or tridentate, or trifid, with short petioles. Very often these have no trace of stipules. The inner or upper leaves of these rosettes are better developed, with elongated petioles, so as to enable them to extend beyond and occupy the space between the short ones. This is

obviously a provision to expose every leaf to light. The stipules of these longer-stalked leaves vary from mere points to subulate or linear, small, brown organs, which being relatively functionless after the expansion of the leaves, soon shrivel up and fall away.

At or near the base of the elongated leafy shoots fairly well-developed leaves occasionally occur, which have no stipules; but as a rule the stipules in this position are

also well developed (fig. 286). As these shoots elongate and become vigorous, the internodes become longer, and the leaves and stipules larger. The latter, indeed, become

287

288

RIBES SANGUINEUM.

289

FIG. 287.-Outer bud-scale with three vascular bundles; stipules indicated by lateral

teeth at the tip.

FIG. 288.-Inner bud-scale with broader membranous margin.

FIG. 289.-Intermediate form between bud-scale and leaf. S, stipule.

FIG. 290.-RIBES SANGUINEUM.

Leaf higher up on shoot. S, stipule.