l^i'^l Hodgsun : Foliar Ahscissiun in Citrus 423 



crushed (fig. 3). This crushed appearance is particuhirly noticeable 

 in the abscission zone at the base of the terminal leaflet. 



As abscission nears completion these greatly swollen, gelatinous 

 walls disappear, being apparently completely hydrolysed. This frees 

 the indurated I-shaped portions of the pit membranes and on the 

 slide these can be separated out as such (cf. Jones, 1909). As these 

 are further attacked little club-shaped bars result (fig. 3) which 

 ultimately are entirely hydrolysed. The dissolution of the gelatinized 

 walls frees the abscission cells in the separation layer from one another, 

 leaving them bounded by a vei-y thin delicate tertiary membrane. 



Fig. 2 — An early stage of the abscission process. Shows the marlvod swelling 

 and gelatinization of the cell wall. From the abscission zone at the base of the 

 petiole. Washington Navel Orange. 



That these cells are not degenerating or dead is proven by the fact 

 that after separation they resume growth and active division with the 

 result that a mass of loose tissue is produced. 



The Process of Abscission 

 As to the nature of the preliminary changes in the cell walls prior 

 to the swelling we can only speculate. There is considerable evidence 



