Leaflets may have one or all of these three parts, but the stalks of leaflets are called petiolules and the stipules of leaflets are called stipels. The leaf of the garden bean has leaflets, petiolules, and stipels.
Fig. 100.—Decurrent Leaves of Mullein.
The blade is usually attached to the petiole by its lower edge. In pinnate-veined leaves, the petiole seems to continue through the leaf as a midrib (Fig. [91]). In some plants, however, the petiole joins the blade inside or beyond the margin (Fig. [92]). Such leaves are said to be peltate or shield-shaped. This mode of attachment is particularly common in floating leaves (e.g. the water lilies). Peltate leaves are usually digitate-veined.
Fig. 101.—Two Pairs of Connate Leaves of Honeysuckle.
How to Tell a Leaf.—It is often difficult to distinguish compound leaves from leafy branches, and leaflets from leaves. As a rule leaves can be distinguished by the following tests: (1) Leaves are temporary structures, sooner or later falling. (2) Usually buds are borne in their axils. (3) Leaves are usually borne at joints or nodes. (4) They arise on wood of the current year’s growth. (5) They have a more or less definite arrangement. When leaves fall, the twig that bore them remains; when leaflets fall, the main petiole or stalk that bore them also falls.
Fig. 102.—Linear-acuminate Leaf of Grass.
