6/04/2010

Types of Abscission

In deciduous trees, an abscission zone, also called a separation zone, is formed at the base of the petiole. It is composed of a top layer which has cells with weak walls, and a bottom layer which expands in the autumn, breaking the weak walls of the cells in the top layer. This allows the leaf to be shed.

In woody plants, an abscission layer is formed composed of parenchyma cells bounded on both sides with cork. This layer is found at the base of the leaf petioles in woody angiosperms and gymnosperms and because of the disintegration of the parenchyma layer, the organ, such as a leaf or bark, is separated from the parent plant. Abscission is a natural process of plant growth induced by the plant, in contrast to decaying or falling off due to other causes.

The liberation of a fungal spore by the withering away of an adjoining layer is also called abscission.

Lack of chlorophyll from decreased sunlight

The reduction of chlorophyll production in leaves due to decreased sunlight in the fall explains why some leaves turn yellow. However, the yellow color can attract aphids, so some trees turn the leaves red instead by injecting a bright pigment. The loss of chlorophyll may also contribute to the abscission process.

Source: http://en.wikipedia.org/wiki/Abscission


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