The beginnings of leaf drop starts when an abscission layer is ed between the leaf petiole and the stem. This layer is ed in the spring during active new growth of the leaf; it consists of layers of cells that can separate from each other. The cells are sensitive to a plant hormone ed auxin that is produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; in autumn, or when under stress, the auxin flow from the leaf decreases or s, triggering cellular elongation within the abscission layer. The elongation of these cells break the connection between the different cell layers, allog the leaf to break away from the plant. It also s a layer that seals the break, so the plant does not sap
. Some trees, particularly oaks and beeches, exhibit a behavior kn as "marcescence" wby de s are not shed in the fall and remain on the tree until being blown off by the weather. This is caused by incomplete development of the abscission layer. It is mainly seen in the seedling and sapling stage, although mature trees may have marcescence of s on the lower branches. A number of deciduous plants nitrogen and carbon from the foliage before they are shed and store them in the of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new s or flowers. Function Fallen s covering a patch of ground Deciduous plants in mid- to high latitudes shed their s as temperatures drop in autumn. Plants with deciduous foliage have vantages and disvantages d to plants with evergreen foliage. Since deciduous plants their s to conserve water or to better surviveter weather conditions, they mu
st regrow new foliage during the next suitable grog season; this uses resources which evergreens do not need to expend. Evergreens suffer greater water loss during theter and they also can experience greater predation pressure, especially when small. Deciduous trees experience much less branch and trunk breakage from glaze ice storms when leafless, and plants can reduce water loss due to the reduction in availability of liquid water during coldter days. Losing s inter may reduce damage from insects; repairing s and keeping them functional may be more ly than just losing and regrog them. Removing s also reduces cavitation which can damage xylem vessels in plants. This then allows deciduous plants to have xylem vessels with larger diameters and tfore a greater rate of transpiration (and hence CO2 uptake as this occurs when stomata are ) during the summer growth period. Deciduous woody plants The deciduous characteristic has developed repeatedly among woody plants. Trees include maple,
many oaks and nothofagus, elm, beech, aspen, and birch, among others, as well as a number of coniferous genera, such as larch and Metasequoia. Deciduous shrubs include honeysuckle, viburnum, and many others. Most temperate woody vines are also deciduous, including grapes, poison ivy, Virginia creeper, wisteria, etc. The characteristic is useful in plant identification; for instance in parts of Southern California and the American Southeast, deciduous and evergreen oak species may grow side by side.
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