Growth and Development of Horticultural Crops (1+1)

Abscission of leaves

• Detachment of the older (rather senescent) leaves or leaf fall is a common phenomenon in plants and is called as abscission of leaves. Abscission is quite distinctive in deciduous trees and shrubs of temperate regions in autumn when all the leaves of such plants fall at about the same time giving the plants a naked appearance, the new leaves developing in the subsequent spring.
  
• In evergreen plants there is gradual abscission of leaves, the older leaves fall while new leaves are developed continuously throughout the year. In most of the herbaceous species, however the leaves are not shed even after they die and in many cases are retained in withered dry condition even after the whole shoot is dead.
• Leaf abscission takes place at the base of the petiole which is internally marked by a distinct zone of few layers of thin-walled cells arranged transversally across the petiolar base. This zone is called as the abscission zone or abscission layer. The cells of the abscission layer separate from each other due to the dissolution.