Leaf fall is a natural stage of life cycle of plants. Autumn sheds the leaves is not a direct consequence of the deteriorating weather conditions, it is fixed hereditary property of the plant. The signal for the beginning of fall is not the temperature drop as you might think, and change the length of a day is the most faithful and constant sign of the onset of autumn. This is confirmed by a very simple experiment. If in the summer you could put it in a pot of soil some young deciduous tree, for example, Dubok or maple, and put it in the bathroom or in the greenhouse in the fall, he will inevitably lose their leaves, despite the best care and warmth.
Nature has ensured that the separation tree leaf has been painless for him. Preparing for fall begins in advance. At the end of summer at the base of the leaf petiole is formed special separating (cork) layer. The cells of this layer have a smooth wall and can therefore easily separated from each other.
in the Fall, before the fall, the connection between the cells of the cork layer is disturbed. The sheet is left hanging on the tree only through the vascular bundles, which connect the leaf to the branch. In the summer these beams serve to conduct water and mineral salts from the roots to the leaves and nutrients produced by the leaves to other parts of the plant. Vascular bundles can be easily visible with the naked eye on the leaf scars in the form of three, five or more major points.
A relatively small mechanical impact, for example, a gust of wind that was broken and this last link between the petiole and the parent plant. Leaves can fall in absolutely calm weather under the influence of gravity leaf blades.
On the site of the scar from the cut out sheet forms a protective cork layer.