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The method of compounding or branching follows the mode of veining. The veining, or venation, is of two general kinds: in some plants the main veins diverge, and there is a conspicuous network of smaller veins; such leaves are netted-veined. They are characteristic of the dicotyledons. In other plants the main veins are parallel, or nearly so, and there is no conspicuous network; these are parallel-veined leaves (Figs. 89, 102). These leaves are the rule in monocotyledonous plants. The venation of netted-veined leaves is pinnate or feather-like when the veins arise from the side of a continuous midrib (Fig. 91); palmate or digitate (hand-like) when the veins arise from the apex of the petiole (Figs. 88, 92). If leaves were divided between the main veins, the former would be pinnately and the latter digitately compound.

Fig. 91.—Complete Leaves of Willow.

Fig. 92.—Digitate-veined Peltate Leaf of Nasturtium.

Fig. 93.—Pinnately Compound Leaf of Ash.

It is customary to speak of a leaf as compound only when the parts or branches are completely separate blades, as when the division extends to the midrib (Figs. 90, 93, 94, 95). The parts or branches are known as leaflets.