1918] Kendall: Abscission of Flowers and Fruits in Solanaceac 417 



It has been noticed in all the experiments detailed above that 

 older flowers are less subject to "spontaneous" abscission than 

 younger ones. The transition line as to size or age beyond which 

 no abscission occurs can not in most cases be definitely drawn ; that 

 is to saj T , the development of a resistance to stimuli takes place grad- 

 ually. This is probably explained by the fact that cell walls gradually 

 become less subject to hydrolysis with age. The celluloses and pec- 

 toses lose water with age and it is well known that these compounds are 

 subject to hydrolysis in proportion to the amount of water they con- 

 tain. In those cases where the increase in resistance to stimuli takes 

 place suddenly it is necessary, as suggested above, to assume some 

 kind of inhibitor of the enzymatic action. 



The effect that pollination has in hastening abscission of the 

 corolla is a subject which is related to the phenomena described by 

 Pitting (1909) for orchids. The phenomena are as yet only slightly 

 understood. The explanation seems to involve some relaying of 

 stimulus from cell to cell. This is also involved in the explanation of 

 floral abscission induced by injury to the ovary. These two cases 

 and others indicate that in some instances, at least, abscission responses 

 are related to tropistic responses as Fitting (1911) has suggested. 



Finally, attention may be called to the fact that the most pressing 

 need in connection with all the problems mentioned above is, in the 

 first place, to establish by some experimental means a definite connec- 

 tion between some enzymatic body and the process of abscission and, 

 in the second place, more definite knowledge as to the role which cell 

 turgor plays in cell separation. Taking all the facts into considera- 

 tion, it is evident that abscission is fundamentally a physiological 

 problem, the crux of which lies, as in all such problems, in the bio- 

 chemistry of the cell. 



The studies reported upon above were carried on under the direc- 

 tion and supervision of Professor T. H. Goodspeed and I am under 

 deep obligation to Professor F. E. Lloyd for many valuable sugges- 

 tions both throughout the course of the experiments and during the 

 preparation of this report of them. 



