Page:British Flowering Plants.djvu/22

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when it has small acute indentations and rounded projections (fig. 34), dentated when it has obtuse incisions and pointed projections (fig. 35), sinuated when it has obtuse incisions and rounded projections (fig. 36), ciliated when the margin is set with fine hairs (fig. 37), incised when the margin exhibits alternately larger; and smaller indentations and projections (fig. 38).

On examining a leaf we find that the softer surface is traversed by hard lines, which are called veins or nerves, and which may be either simple or branched, and sometimes form a network.

When the veins run straight they are called parallel (figs. 39 and 40), but they are frequently curved. Reticulated leaves are called digitate when equally thick veins subdivide towards the ends (fig. 41), and pinnate when there is one midrib forming a continuation of the leaf-stalk, and throwing out slender branching veinlets on the sides (fig. 42).

Hitherto we have been speaking of simple and undivided leaves, but many plants exhibit leaves more or less divided.

When the division is incomplete the leaf is