A typical leaf is made up of three main parts:
A leaf that has only one blade is called a simple leaf, however some simple leaves such as those of the Oak tree have deep 'V's or other indentations along their edges.
Compound leaves consist of a number of separate blades called leaflets. The leaflets are usually lined up in two rows one on each side of the leafs main axis. The axis of a compound leaf is called the rachis, e.g. Rose leaves. Many other plants including clovers have compound leaves with only three leaves spreading out from the tip of the petiole.
The blade is the broad part of a leaf that holds the green food making cells.
The petiole is the stemlike part of the leaf which holds the blade. A leaf petiole is not merely the handle which holds the leaf to the plant it must also carry food made by the leaf to all parts of the plant. A petiole is made up of tiny tubes held together tightly like a handful of drinking straws, petioles grow to various lengths on the same plant. They grow extra long if the plant is shaded but stay short if no other leaf blades cut off the light. A petiole will also twist to keep the blade with its turned face to the sun. As a result of this behaviour of petioles the leaves on a tree form a pattern in which few leaves are shaded by other leaves. The base of the petiole is wider than the rest of the leaf stem and is firmly attached to the stem of the plant on which it grows.
In addition to the blade and petiole, the leaves of some plants have stipules. Most stipules are shaped like tiny leaves. They add to the food making power of the blade. Rose leaves have stipules that look like pairs of tiny leaves attached to the base of each petiole. Other stipules have special uses, some are pairs of heavy spines for protection. Smilax (Asparagus asparagoides) has long wiry stipules that wind around twigs and support the plant.
Photosynthesis is a food making process that occurs in green plants. It is
the chief function of leaves. Green plants combine energy from light with water
and carbon dioxide to make food. All our food comes from this important energy-converting
activity of green plants. Food energy originally comes from light and is stored
in food made by green plants. Animals eat the plants and human beings eat animal
products as well as plants.
The light used in photosynthesis is absorbed by a green pigment called chlorophyll. In plant cells chlorophyll is contained in bodies called chloroplasts.
Green plants convert carbon dioxide and water into food and oxygen. In the process, carbon dioxide and water are returned to the atmosphere, thus the carbon and oxygen balance on earth is maintained.
Parts of a simple leaf
Parts of a compound leaf