The controlled shedding of a part, such as a leaf, fruit, or flower, by a plant. The process is usually associated with a decline in auxin level within the organ to be detached. An abscission zone of tissue often forms at the point of separation, which is normally at the base of a petiole or pedicel. A thin plate of cells, the abscission (or separation) layer, forms within the abscission zone. The pectic acid in the cell walls of the abscission layer is converted to pectin, resulting in a softening and weakening of the region. The organ is then easily dislodged from the plant by wind, heavy rain, etc. Abscisic acid, which promotes leaf senescence, may also play a part in abscission. Ethylene has been shown to accelerate the abscission of senescent leaves. Precocious abscission of fruits (fruit drop
) is a common phenomenon.