The Forms of Leaves
Leaves axe described as simple or compound, depending on whether they have one or a number of blades. They are described also by their shapes and their margins (edges).
A simple leaf, or the leaflet of a compound leaf, may be lance-shaped, oval, elliptical, heart-shaped, or any of a large number of other shapes. The margin may be entire (smooth and unindented, as in corn); serrated (saw-toothed, as apple and elm leaves); waved (having rounded projections, as in the chestnut oak); or lobed (with deep indentations, as in oak and maple leaves). Pinnately lobed leaves (such as those of the oak) have indentations pointing toward the central vein. Palmately lobed leaves (maple leaves, for example) have indentations that point toward the base of the blade.
A compound leaf consists of a number of leaflets. The leaflets look like leaves, but buds do not grow in their axils, as they do in the axils of true leaves. In a pinnately compound leaf the leaflets grow from both sides of the petiole, as the barbs grow from the shaft of a feather. The leaflets of a palmately compound leaf grow from the tip of the petiole. Doubly compound leaves have leaflets made up of still other leaflets.