1918] Kendall: Abscission of Flowers and Fruits in Solanaceae 377 



separation cells are, comparatively speaking, very small, but also be 

 cause of the fact that the walls of these cells fail to show any strati- 

 fication. 



Iodine, Delafield's haematoxylin, Ruthenium red, Bismark brown, 

 methylene blue, erythrosin, and eosin were used with little success in 

 most cases. By using iodine, however, just as abscission is known to be 

 commencing, a white streak may be seen across the section in the region 

 of the separation layer. Upon careful examination it was decided 

 that this white streak was due to the failure of most of the cell walls 

 in the separation layer to take the stain. Although it is probable 

 that with more careful examination the other stains mentioned above 

 would give similar results, it was found that methylene blue was the 

 only stain with which anything definite could be established. If a 

 thin longitudinal section cut in paraffin as abscission is known to be 

 starting, and stained in methylene blue, is examined (cf. page 361), it 

 will be found that the walls of those cells in which separation is about 

 to occur have remained almost entirely unstained. The protoplasts in 

 these cases seem to be surrounded only by the thin tertiary mem- 

 branes, between which is a streak of colorless material of varying 

 width (pi. 51). Cell walls where separation is not expected to occur, 

 however, stain a dark blue throughout in the normal manner. 



An examination of freshly isolated cells washed oft 2 from the end 

 of an abscissed pedicel shows that these cells are still turgid and 

 active. It was impossible to determine whether these cells had in- 

 creased in size, as compared with the size of similar cells before abscis- 

 sion, but it is evident that the increase, if any, had not been very 

 great. The cells still contain their large nuclei, and occasional starch 

 grains, and show after isolation no signs of degeneration even after 

 several hours in water. In addition, these isolated cells appear to have 

 retained their original shape. In the collenchyma of Datura the cells 

 are from five to eight times as long as wide, and yet these cells retain 

 their original shape when isolated, as a result of the dissolution of 

 the middle lamellae. This isolation has evidently not been complete, 

 since large masses of cells are seen still attached to each other. It is 

 noticed that in all cases the protoplast is surrounded by an extremely 

 thin membranous wall (pi. 52, fig. 3). It is also frequently noticed 

 that the protoplast seems drawn away from the cell wall as if plas- 

 molysis had occurred. It is possible that this appearance may be due 

 simply to the gathering together of granules and the denser portion 

 of the protoplasm in the center of the cell. 



