1918] Kendall: Abscission of Flowers and Fruits in Solanaceac 383 



The normal acidity in Datura is high, but it is doubtful whether 

 the increase is large enough to account for the dissolution of the 

 middle lamella. At any rate, it is certain that acidity does not enter 

 into the problem in the pedicel of Nicotiana. We must, therefore, 

 fall back upon the enzyme action as probably responsible for the 

 process of cell separation. 



Most hydrolysing processes characteristic of living cells aFe now 

 supposed to be due to the action of enzymes of different kinds. It 

 has been definitely claimed (cf. Atkins, 1916) that an enzyme which 

 has been called pectosinase is capable of breaking down the pectose 

 of which the middle lamella is composed. Add to this the fact that the 

 action of enzymes has been shown, as has also the process of abscission, 

 to be very sensitive to all kinds of changes in the external environment, 

 and it is fairly safe to assume that the method of cell separation is 

 fundamentally an enzyme problem. Irrefutable proof of this could 

 be obtained only by testing for the activity of pectosinase during the 

 early stages of abscission and by demonstrating the absence or in- 

 activity of this enz3 r me in species where abscission does not occur. 



ABSCISSION OF THE STYLE AND COROLLA 



Abscission of the corolla in Nicotiana was described by Kubart 

 and it may be said at once that the observations herein described 



agree entirely with his. Abscission of the 

 corolla is brought about by the separation, 

 without any previous cell divisions or 

 elongations, of living cells at the base of 

 the corolla tube. The separation layer, 

 which is in no way morphologically differ- 

 entiated from the neighboring tissue, is 

 located about 1 mm. from the point of in- 

 sertion of the corolla on the receptacle. It 

 thus occurs in the distal part of a region 

 where intergradation of cell shape, between 

 the isodiametric cells of the receptacle 

 and the more or less elongated cells of the 

 corolla, is apparent. The separation cells 

 which are in this region of intergradation 



Fig. 6. Longitudinal radial . . 



section of the base of the are not isodiametric but are more or less 



corolla tube of Nicotiana, elongated parallel to the long axis of the 

 showing the method of ab- 

 scission, corolla. All the cells in cross-section of the 



