Defoliation

After the first frost, they are beginning to crumble the masses, and the earth is covered with a layer of rustling leaves. Yellowing leaves are often occurs long before the autumn days. Scattered yellow leaves appear in mid-summer. In very dry and hot years partial yellowing occurs much earlier than the autumn, especially in the birches. Complete yellowing of birch is much later than their first appearance on the yellow strands. Different trees become a different fall color, along with that some remain green for a long time (eg, lilac). Color change indicates that the role of the leaves have already finished, and they cease to produce organic nutrients. Even before the colorization of foliage remaining in its nutrients move into the branches, trunk and roots of a tree. There they remain until spring of next year. While the process of their movement has not ended, massive defoliation has not yet come. Already in the late summer at the base of the petiole leaf begins the formation of a special cork layer, a sort of wall that separates the stalk from the branches. Cells of this layer is smooth walls, and the relationship between them can be easily broken. By the beginning of leaf fall leaf is usually kept on a branch only because of the vascular bundles, piercing detachable partitions and these bundles - only now the connection plate and the stem with a branch. This relationship is very fragile, and only a light gust of wind that "strings", which keeps the stalk, broken. A leaf falls. He can come off and fall, even a bit of otyazhelev settled on it dew. In the biological significance of drop leaf can be seen in those years when it is too early snow or sleet caught the trees have not yet liberated from the leaves. Heavy snow or freezing in the cold rain moisture load the tree such severity that the thin trunks of the trees bend down to the ground, tops, branches and even thick branches break. In these cases, in the gardens of fruit trees are severely injured. Whoever has seen this picture, for obvious vital importance of the timely release of trees from the leaves before the onset of winter weather. But the main value of leaf fall is not the point, he - the adaptation of plants to winter drought. Deciduous trees, left for the winter in the leaves, would have perished from lack of moisture. The flow of water in the winter in plant negligibly weak evaporation as it leaves no would cease. Comparison of the deciduous trees with conifers - pine, spruce - clearly shows the value of leaf fall. Spruce, pine and especially drought-resistant, their needles evaporates water is many times smaller than the leaves of deciduous trees. For example, birch evaporate over the summer on 100 g dry matter of leaves 81.4 kg of water, and pine - just 9.4 kg, ie, almost 9 times smaller. Falling for the winter larch evaporates a lot of water - 10 times more than the pine. Larch conifer species, but the evaporation of water is similar to the hardwoods. Observation. 1. Set the date yellowing of vertices and a complete change in color of the leaves of birch, aspen, maple and other tree species. 2. Note the date of the first significant decline of birch leaves and the beginning of mass leaf fall. 3. Spend the same observation over other tree species where you live. 4. Record the time the first frost in the soil and air. 5. When there was a full exposure of birch, aspen and oak?