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University of California Publications in Botany [VOL. 5 



base of the corolla tube at about the level of the separation layer seem 

 to be involved in the process except the epidermal cells and the 

 tracheae. The process of cell isolation in this case may spread up and 

 down for quite a distance between the epidermis and tracheae, thus 

 involving a large number of cells (fig. 6). 



Abscission of the corolla in Datura differs slightly from that in 

 Nicotiana,. As in the latter, there is no differentiated separation 

 layer, separation occurring in cells which are not visibly different 

 from other cells of the corolla. Cells more or less elongated are in- 

 volved, as in Nicotiana, but in Datura the region of separating cells 

 is limited to certain tissues that is to say, not all the cells across 

 the base of the corolla tube at about the level of the separation layer 

 are involved in the process of abscission. The base of the corolla in 

 Datura is characterized by distinct longitudinal ridges which alternate 

 with deep grooves. Thus, a cross-section of a portion of the base of 

 the corolla appears as in fig. 8. Cell separation fails to occur in the 

 outside ridges at the level of the separation layer, so that, looking at 

 the base of the corolla tube from the outside during abscission, one 

 sees separate crescent-shaped regions of macerating cells alternating 

 with cells which are not separating (fig. 7). This is explained when 

 a cross-section is taken (fig. 8), which shows that several vascular 

 bundles, the cells of which do not sep- 

 arate, are collected in the outside ridges. 



Abscission of the style occurs nor- 

 mally in Nicotiana and Datura a short 

 time before the corolla has fallen. So 

 far as it was possible to determine, the 

 process of abscission is exactly the same 

 in the style as in the corolla. A separa- 

 tion of very small, more or less elongated 

 cells takes place at the base of the style 

 without any external indication such as Fig. 7 



frequently occurs in the pedicel of the c region of separating cells. 



'a c 

 Fig. 8 



a vascular bundle. 

 c region of cell separation. 

 5 region of no cell separation, 



