1918] Kendall: Abscission of Flowers and Fruits in Solanaceae 379 



number of pedicels in which no abscission had started. The extracts 

 were made up to 10 cc. and the precipitate obtained with 60 cc. of 

 95 per cent alcohol. The precipitate weighed in the two lots : 



A 996 nig. 



B : 903 mg. 



One of the preliminary experiments performed with~~a "weaker 

 alcohol gave results which may or may not be of considerable impor- 

 tance. In this experiment a light, almost invisible precipitate formed 

 in A and no precipitate in B. Whether or not the pectins precipitate 

 in lower percentages of alcohol more readily than the other substances 

 I have been unable to determine. At any rate, the precipitate in this 

 case felt slimy and mucilaginous to the touch and might well have 

 been the precipitated pectin approximately pure. 



d. EVIDENCE FOE INCEEASE IN TUEGOE 



It was stated along with other conclusions in the preliminary paper 

 (Goodspeed and Kendall, 1916) that from the evidence at that time 

 available it was probable that cell separation is caused merely by an 

 increase in cell turgor, and throughout this later work it has been 

 clear that increased turgor is present during abscission. In view of 

 the evidence given above, however, it would seem that turgor can 

 play only a secondary role, although the occurrence of increase in 

 turgor must not be ignored. 



The bulging of the epidermis frequently noted as accompanying 

 abscission is evidence of increased internal pressure. In the pith the 

 cells next to those which are separating are in a collapsed condition 

 due to the pressure of the expanding separating cells. By various 

 experiments it can be shown that humid conditions favor and severe 

 drought prevents abscission. Richter and others have shown that 

 narcotic vapors which cause abscission also cause increased turgor by 

 increasing the proportion of sugar in starch-containing cells. This 

 increase in cell turgor becomes so great as to cause complete macera- 

 tion in certain types of tissues. The frequent presence of starch 

 grains in the separation layer of Nicotiana, part of which are prob- 

 ably converted into sugar as a result of subjection to illuminating 

 gas, indicates that there is probably an increase of turgor during 

 abscission, at any rate when induced by illuminating gas. 



On the other hand, a more extensive examination of abscission in 

 certain plants indicates that all evidences of increased turgor may at 



