Leaves
Leaves are often the most conspicuous part of any plant. Leaves vary tremendously in shape and in size: from the tiny leaves (less than 1 millimeter across) of the floating aquatic plant duckweed to the giant leaves (more than 10 meters in length) of the raffia palm. Nevertheless, all leaves share certain features of construction and development and carry out the same basic function: photosynthesis.
Leaf Types
Leaves are designed to optimize the capture of light for photosynthesis. In dicots, leaves typically have a broad, flattened blade attached to a stalk or petiole. The flat shape of the blade facilitates the penetration of lightinto the photosynthetic tissues within, while the petiole positions the blade so that it is shaded as little as possible by neighboring leaves. Leaf blades are referred to as simple when they are undivided and as compound when they are subdivided into individual leaflets. Compound leaves are either pinnately compound (like a rose leaf) or palmately compound (like a horse chestnut leaf). Simple leaves may also have complex shapes: In plants such as the maple or oak, leaves are highly lobed. The lobing of simple leaves and dissection of compound leaves are thought to serve the same function: The leaf maintains a large photosynthetic surface, but the complex outline allows the leaf to radiate heat energy to the surrounding atmosphere, thus maintaining photosynthetic tissues at optimum temperatures.
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