Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/121

Rh SIMPLE LEAVES.] BOTANY 111 the divisions extend nearly to the base or to the midrib the leaf is partite, and its lines of separation are called partitions. VI Fig. 100. FIG. 104. Ovate acute leaf of Coriara myrtifotia, one of the adulterations of senna. Besides the midrib there are two infra-marginal ribs which converge to the apex. The leaf is therefore tricostate. FIG. 105. Runcinate leaf of Dandelion (Leontodon Taraxacum). It is a pinnatifid leaf, with the divisions pointing towards the petiole. FIG. 106. Pinnatifid leaf of Valeriana dioica. If these divisions take place in a simple feather-veined leaf it becomes either pinnatifid (fig. 106), when the segments extend to about the middle and are broad ; or pectinate, when they are narrow; or pinnatipartite, when the divisions extend nearly to the midrib. These primary divisions may be again subdivided in a similar manner, and thus & feather-veined leaf will become bipinnati/id or bipinnatipartite ; and still further subdivisions give origin to tripinnatifid and laciniated leaves. If the divisions of a pinnatifid leaf are more or less triangular, and point downwards towards the base, the extremity of the leaf being undivided and triangular, the leaf is runcinate (fig. 105), as in the Dandelion. When the apex consists of a large rounded lobe, and the divisions, which are also more or less rounded, become gradually smaller towards the base, as in Barbarea, the leaf is called lyrate, from its resemblance to an ancient lyre. When there is a concavity on each side of a leaf, so as to make it resemble a violin, as in Rumex pulcher, it is called panduriform. The same kinds of divisions taking place in a simple leaf with radiat ing venation, give origin to lobed, cleft, and partite forms. When the divisions extend about half-way through the leaves, they may be three-lobed, five-lobed, seven-lobed, many-lobed, or trifid, quinquefid, septemfid, multifid, ac cording to the number of the divisions. The name pal mate, or palmatifid (fig. 101), is the general term applied to leaves with radiating venation, in which there are several lobes united by a broad expansion of parenchyma, like the palm of the hand, as in the Castor oil plant, Rheum palma- tum, and Papaw. The divisions of leaves with radiating ven ation may extend to near the base of the leaf, and the names bipartite, tripartite, quinquepartite (fig. 107), septempartite, dig tripartite (Plate II. fig. 1), are given according as the partitions are two, three, five, seven, or more. In Droscra dichotoma bipartite and tripartite leaves are seen. The term dissected is applied to leaves with radiating venation, having numerous narrow divisions, as in Geranium dissectutn. When in a radiating leaf there are three primary partitions, and the two lateral lobes are again cleft, as in Helleborus Fur. 1 07. 108. FIG. 107. Five-partite leaf of Aconite. Such a leaf is sometimes called palmi- partite, palmately-partite, or dissected. The venation is radiating, and the segments of the leaf are cuneate, and each of them is cleft and toothed at the apex FIG. 108. Pedate leaf of Stinking Hellebore (Hellfborusfcetidus). The venation is radiating. It is a palmately-partite leaf, in which the lateral lobes are deeply divided. When the leaf hangs down it resembles the foot of a bird, and hence the name. (fig. 108), the leaf is called pedate or pedatifid, from a fancied resemblance to the claw of a bird. In all the instances already alluded to the leaves have been considered as flat expansions, in which the ribs or veins spread out on the same plane with the stalk. In some cases, however, the veins spread at right angles to the stalk. If they do so equally on all sides, and are united by parenchyma, so that the stalk occupies the centre, the leaf becomes orbicular, as in Hydrocotyle ; if unequally, so that the stalk is not in the centre, the leaf is peltate, as in Indian Cress (fig. 109). The edges or margins of orbicular and peltate leaves are often variously divided. FIG&quot;. 109. Peltate leaves of Indian Cress (Tropao um majus). FIG. 110. Lanceolate leaf of a species of Senna. Without attempting to notice all the forms of leaves, the following are enumerated as the most important. When the veins do not spread out, but run from the base to the apex with a narrow strip of parenchyma, the leaf is linear or acicular, as in Pines and Firs. These trees are hence called in Germany Nadel-holzer, or needle trees. When the veins diverge, those in the middle being longest, and the leaf tapering at each end (fig. 110), it becomes lanceolate. If the middle veins exceed the others slightly, and the ends are convex, the leaf is either rounded, elliptical, oval, or oblong (fig. 111). If the veins at the base are longest, and the leaf narrows to the top, it is ovate or egg-shaped (fig. 104), as in duckweed; if the apex is broadest, the leaf is obovate, or inversely egg-shaped (fig. 112). Leaves are cuneate or wedge-shaped, in Saxifraga ; spathulate, or spatula-like, having a broad rounded apex, and tapering