Fig. 112. Leaf of the Quince: b, blade; p, petiole; st, stipules.
[126.] Venation is the name of the mode of veining, that is, of the way in which the veins are distributed in the blade. This is of two principal kinds; namely, the parallel-veined, and the netted-veined.
127. In Netted-veined (also called Reticulated) leaves, the veins branch off from the main rib or ribs, divide into finer and finer veinlets, and the branches unite with each other to form meshes of network. That is, they anastomose, as anatomists say of the veins and arteries of the body. The Quince-leaf, in Fig. [112], shows this kind of veining in a leaf with a single rib. The Maple, Basswood, Plane or Buttonwood (Fig. [74]) show it in leaves of several ribs.
128. In parallel-veined leaves, the whole framework consists of slender ribs or veins, which run parallel with each other, or nearly so, from the base to the point of the leaf,—not dividing and subdividing, nor forming meshes, except by minute cross-veinlets. The leaf of any grass, or that of the Lily of the Valley (Fig. [113]) will furnish a good illustration. Such parallel veins Linnæus called Nerves, and parallel-veined leaves are still commonly called nerved leaves, while those of the other kind are said to be veined,—terms which it is convenient to use, although these "nerves" and "veins" are all the same thing, and have no likeness to the nerves and little to the veins of animals.
129. Netted-veined leaves belong to plants which have a pair of seed-leaves or cotyledons, such as the Maple (Fig. [20], [24]), Beech (Fig. [33]), and the like; while parallel-veined or nerved leaves belong to plants with one cotyledon or true seed-leaf; such as the Iris (Fig. [59]), and Indian Corn (Fig. [70]). So that a mere glance at the leaves generally tells what the structure of the embryo is, and refers the plant to one or the other of these two grand classes,—which is a great convenience. For when plants differ from each other in some one important respect, they usually differ correspondingly in other respects also.
Fig. 113. A (parallel-veined) leaf of the Lily of the Valley. 114. One of the Calla Lily.