The leaf is the lateral vegetative organ of the shoot.It plays an important role in the life of the entire plant, the structure of the sheet is arranged so that it is able to adapt to environmental conditions to perform its functions - photosynthesis, evaporation and gas exchange, guttation. The sheet can be modified and represent a needle (like a coniferous tree) or a thorn (for cacti and barberry, etc.). Such transformations of the side branches of the shoot help plants survive in different climatic zones.
Morphological structure of the leaf also provesthe presence of simple and complex forms. The main assimilating organ of a plant is called simple if it has one petiole and one leaf plate, which fall completely (maple, lilac, willow). Complex leaves have 1 petiole and several leaf blades that can fall separately (walnut, chestnut, ash).
The internal structure of the sheet is identical for allplants. The leaf plate on top and bottom is covered with a layer of epidermis, which forms the skin. Some representatives of the flora on the upper skin may have hairs, cuticle film or a wax coating. These are all protective devices that prevent overheating, burns, excessive evaporation of water. The integumentary tissue in most plants, on the underside of the leaf, has slotted holes - stomata, which have two closing cells. Through the stomatal apparatus pass gases and water vapor, both into the lateral organ of the shoot itself, and outward.
Thus, the structure of the sheet is very complex andis due to the functions performed by this body - assimilation, gas exchange, gutation and evaporation. Also, in addition to the basic, the sheet can also perform additional functions - protection (spines), a stock of substances (scales of bulbs) and vegetative reproduction.