﻿LLOYD— ABSCISSION 



3. The walls of all the cells of the abscission zone, as denned 

 in this paper, are altered chemically during abscission. The great- 

 est degree of alteration takes place in the cells which are actually 

 involved in separation (namely, those of the separation layer), 

 in which the alteration, by hydrolysis, proceeds so far as to procure 

 the complete digestion of a part of the primary and secondary 

 walls, thus allowing a great extenuation of the tertiary walls, their 

 separation from each other, and from the only partially altered 

 primary and secondary walls of the next distal tier of cells. 



4. The separation layer is composed of one tier of cells only in 

 very young organs, and from 1 to 5 in older. Of these tiers, usually 

 only the uppermost proceeds to complete separation. Mechanical 

 resistances, which are greater in older parts, appear to influence 

 the direction of the plane of separation. 



5. The behavior of starch in the separation layer and adjoining 

 tissues during abscission indicates that it is a source of energy 

 for the separation cells during their growth. 



6. The final separation results from the digestion of portions 

 of the primary and secondary cell walls of the separation cells, 

 leaving the protoplasts invested by a tertiary membrane which 

 grows independently of adjoining membranes, from which it is 

 quite free. 



7- Neither the cytoplasm, nor the nuclei, nor any part thereof, 

 displays degeneration changes. On the contrary, cytoplasm, nuclei, 

 and nucleoli bear evidence of greater physiological activity, and 

 are quite alive and normal when separation is achieved. There 

 is meanwhile no loss of turgor. 



Conclusion 



From the foregoing facts it is concluded that abscission in 

 Mirabilis is not procured by a separation resulting from the com- 

 plete solution and destruction of a layer of tissue, as held by 

 Haxnig, and does not therefore constitute a new type of abscission. 

 Contrariwise, the mode of abscission accords wholly, as to all 

 essential details, with that which has been shown to occur in such 

 forms as Gossypium, Arisiolochia, etc. 



