There comes the fall, day becomes shorter, leaves on trees turn yellow, redden and are twisted, and then fall down at all. The leaf fall is very beautiful phenomenon but why trees throw off every fall the clothes? The fact is that so the tree saves own resources.
Why in general to trees leaves? Everything is simple. In leaves there is a process extremely important for active activity of a tree. It is photosynthesis during which the chlorophyll necessary for production of wood juice which is also called crude turpentine is synthesized. But photosynthesis can be carried out in leaves only in the presence of the comfortable temperature (for various trees it rather strongly varies) and also only at sunlight. When there comes the fall, there comes cold weather, and the chlorophyll in leaves collapses. Other pigments which are present at a leaf too, but are not visible because of overwhelming advantage of a chlorophyll, act on the foreground, and the leaf loses the bright green coloring, being painted in other colors. The yellow pigment is called xanthophyll, and red – carotene, they prevail in coloring of a leaf in autumn time. These substances are necessary for leaf life, but they are not really necessary to the tree. It needs only a chlorophyll which leaves do not make any more. Still water is necessary for a tree, and it circulates on a trunk, getting to leaves. If liquid arrives in excess quantity, then through leaves it evaporates. But even if water is not enough, then a part it all the same leaves a tree through a surface of leaves, not to mention their food. It turns out that in the fall leaves not only become useless, they also spend valuable water which because of cold weather the roots and so practically do not absorb. For this reason trees dump the any more necessary leaves in the fall, and then fall into "hibernation" before spring. It is also the reason of a leaf fall which is just protective reaction of a tree that there come adverse times. Leaves leave a tree, without harming it at all. If to tear off a leaf from a branch in summertime, on a surface of a tree small "wound" is formed. But in the fall the basis of a shank has so-called pith cages. The layer carries out roles of a peculiar layer between fabrics of a tree and a leaf from them. The shank on a branch keeps by means of very thin fibers. Once small wind blows, fibers break, the leaf falls. A hem are not formed as the pith layer reliably protects a tree surface.