A leaf is a thin, flattened outgrowth of a plant that is often green and usually serves as the plant’s tissue. The leaves are attached to the plant via joins called petioles.
Leaves are involved in many plant processes and are always the site of photosynthesis. Leaves also play a role in transpiration, providing energy for the plant by evaporating water from the stomata on their undersides.
In plants with true leaves, the sporophyte generation produces them by growing new cells at the tips of shoots. This contrasts with spore-bearing ferns and mosses that produce spores inside their capsules, which then produce gametophytes that grow into new plants.
A leaf can be thought of as a flat structure composed of two layers: an upper epidermis consisting of one or more layers of cells (called palisade mesophyll) and beneath this a lower layer called the spongy mesophyll that consists mainly of tracheids (vascular tissue), xylem (woody) and phloem (soft).
The vascular bundles in leaves are arranged such that they do not cross each other. This way, there is no direct connection between any two points in the leaf except at its base where.
Last modified: July 31, 2022