Leaf - lateral vegetative organs escape.It plays an important role in the life of the plant, the structure of the sheet is arranged so that it is able to adapt to the environment to perform its functions - photosynthesis, evaporation and gas exchange Guttation.The sheet can be modified and be a needle (as in softwood) or prickle (cacti and barberry, etc.).Such transformation of the side of the escape help plants survive in different climatic zones.
external structure of a sheet depends on the type of plant.So, distinguish simple and complex, petiolate, sessile leaves and wrapped around.Almost all of the side to escape authorities have widened portion - leaf blade, which can be solid, dissection, or a separate blade.The stalk, which assimilating the main body is attached to the stem, and may be absent altogether, then say that the sheet "sedentary" or beschereshkovy.If the lamina completely surrounds the stem like, it is wound around the side of the body escape.In angiosperms with petiolate leaves have stipules and that protect the young leaves and axillary buds.
morphological structure of leaf also proves the existence of simple and complex forms.Simply referred to as the main body of assimilating plants, if it has one stalk and one leaf blade, which fall entirely (maple, lilac, willow).Compound leaves have a petiole 1 and several leaf blades that can fall off individually (walnut, chestnut, ash).
internal structure of the sheet is identical in all plants.Steel plate coated with the top and bottom layer of the epidermis, which forms the skin.Some of flora on the skin of the upper hairs may be, the film-cuticle or waxy coating.It all safety devices that prevent overheating, burns, excessive evaporation of water.Coating tissue in most plants, with the bottom side of the sheet has a slit-shaped aperture - stomata which have two guard cells.After stomatal apparatus are gases and water vapor itself in lateral escape of body and the outside.
cellular structure of the sheet indicates the presence of the fabric - the mesophyll, which is divided into spongy and palisadnuyu (columnar) parenchyma.The structural units of the columnar tissue contain a huge number of chloroplasts, which are able to move beyond the sunlight.The cells are very closely adjacent to each other, it is in their photosynthesis.The spongy tissue is formed by elementary particles of the living who have an irregular shape, a large amount of intercellular substance themselves very loosely packed. takes part, but not as active as the palisade parenchyma, assimilation, as well as through its airspace gas exchange occurs.Also in the piece are the veins that serve as vessels participating in metabolism.It is for them water with minerals is delivered to cells of lateral body escape, and outputs the sheet itself from organic compounds formed during photosynthesis.Also, the large veins are surrounded by fiber bundles formed by machining the leaf tissue and gives strength.
Thus, the structure of the sheet is very difficult and caused the functions performed by this body - assimilation, gas exchange, Guttation and evaporation.Also, besides the main sheet can perform additional functions - protection (spines), reserve substances (bulb scales), and vegetative propagation.
