LEAVES
Leaves are the green expansions borne by the stem, out-spread in the air and light, in which assimilation is carried on. They may be said to be the stomachs of the plant. A typical leaf consists of three parts—the blade, the foot-stalk (or petiole), and a pair of stipules. Yet any one of these parts may be absent.
The blade is the expanded portion of the leaf and the part to which the word leaf, in its commonest sense, is applied;
the stipules are small, usually leaflike bodies borne at the base of the petiole, usually one on either side;
the petiole is the stalk of the leaf.
Leaves are simple, when having but one blade; compound, when having more than one, when each blade is called a leaflet.
Compound leaves are said to be—
pinnate, when the leaflets are arranged along the sides of a petiole, or rather of its prolongation, the rachis;
abruptly pinnate, with an even number of leaflets;
odd-pinnate, with an odd leaflet at the end;
palmate, or digitate, when the leaflets all diverge from the summit of the petiole, like the fingers of a hand.