130. Parallel-veined leaves are of two sorts,—one kind, and the commonest, having the ribs or nerves all running from the base to the point of the leaf, as in the examples already given; while in another kind they run from a midrib to the margin, as in the common Pickerel-weed of our ponds, in the Banana, in Calla (Fig. [114]), and many similar plants of warm climates.
131. Netted-veined leaves are also of two sorts, as in the examples already referred to. In one case the veins all rise from a single rib (the midrib), as in Fig. [112], [116]-[127]. Such leaves are called Feather-veined or Penni-veined, i. e. Pinnately-veined; both terms meaning the same thing, namely, that the veins are arranged on the sides of the rib like the plume of a feather on each side of the shaft.
132. In the other case (as in Fig. [74], [129-132]), the veins branch off from three, five, seven, or nine ribs, which spread from the top of the leaf-stalk, and run through the blade like the toes of a web-footed bird. Hence these are said to be Palmately or Digitately veined, or (since the ribs diverge like rays from a centre) Radiate-veined.
133. Since the general outline of leaves accords with the framework or skeleton, it is plain that feather-veined (or penni-veined) leaves will incline to elongated shapes, or at least to be longer than broad; while in radiate-veined leaves more rounded forms are to be expected. A glance at the following figures shows this.
Fig. 115-120. A series of shapes of feather-veined leaves.
[134.] Forms of Leaves as to General Outline. It is necessary to give names to the principal shapes, and to define them rather precisely, since they afford easy marks for distinguishing species. The same terms are used for all other flattened parts as well, such as petals; so that they make up a great part of the descriptive language of Botany. It will be a good exercise for young students to look up leaves answering to these names and definitions. Beginning with the narrower and proceeding to the broadest forms, a leaf is said to be
Linear (Fig. [115]), when narrow, several times longer than wide, and of the same breadth throughout.