The Parts of A Leaf
A typical leaf consists of a leafstalk, or petiole; and an expanded blade, or lamina. The petiole connects the blade to the stem. (Leaves that do not have petioles are called sessile.) In some plants a pair of stipules grows from the petiole, below the blade. These are mere shreds in some plants, and large and leaflike in others. In some plants they have developed into spines or tendrils.A broad leaf consists of a leafstalk, or petiole; and an expanded blade, or lamina.
Tiny tubes within the petiole carry a watery solution of minerals to the blade, and conduct food from the blade to the stem. As a rule, petioles turn blades toward the light, but in plants such as the compass plant they turn them away from it.
is usually broad, flat, and thin. It is hairlike in some grasses, tubular in onions, scalelike in cedars, and needlelike in pines. Sedums and a number of other plants have fleshy blades that store water.
Within the blade, the tubes that pass through the petiole branch out into a network of veins. The veins carry liquids to and from the cells within the blade. They also help to keep the blade extended.
There are two basic ways in which the veins are arranged within a leafparallel and netted.
Parallel veins, such as those in the leaves of most grasses, run side by side from the base to the tip of the blade. Pinnately parallel veins, such as those of banana leaves, branch out from a central vein running the length of the leaf. The branches are parallel to each other in the same way that the barbs of a feather are parallel.
In pinnately netted leaves the veins extend outward from a central vein, like branches of a tree, but are not parallel to each other. Elms and oaks have such arrangements. In palmately netted leaves, such as those of the sycamore and maple, the largest veins branch out somewhat like outspread fingers. From each large branch there are smaller branches.