leaf (lēf) Pronunciation Key
(click for larger image in new window) An appendage growing from the stem of a plant. Leaves are extremely variable in form and function according to species. For example, the needles of pine trees, the spines of cacti, and the bright red parts of the poinsettia plant are all leaves modified for different purposes. However, most leaves are flat and green and adapted to capturing sunlight and carbon dioxide for photosynthesis. They consist of an outer tissue layer (the epidermis) through which water and gases are exchanged, a spongy inner layer of cells that contain chloroplasts, and veins that supply water and minerals and carry out food. Some leaves are simple, while others are compound, consisting of multiple leaflets. The flat part of the leaf, the blade, is often attached to the stem by a leafstalk. |
leaf definition
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