1918] Kendall: Abscission of Flowers and Fruits in Sol-ana-ceae 409 



quickly, thus permitting several coats to be applied. It was doubtful 

 whether other substances, such as lard, cocoa butter or vaseline, which 

 might have been used, would not have been prevented from completely 

 covering the flower in one coating by the presence of numerous hairs 

 and glandular fluid on the calyx. In this experiment flowers were 

 immersed in melted paraffin to within a millimeter of the separation 

 zone and allowed to stand in water under normal atmospheric condi- 

 tions. As a test for abscission, the shoot was shaken or individual 

 flowers tapped from time to time. It was found that several Nicotiana 

 varieties and hybrids differed in their reaction to this treatment as 

 they did in their reaction to illuminating gas. In A T . Tabacum " Mary- 

 land," for example, paraffining the flowers failed to cause abscission 

 for six days, at the end of which time the flowers began to fall, as did 

 those of the control. Some varieties, however, under such treatment, 

 throw off buds at the end of twenty-four hours, but open flowers of 

 the same varieties are never shed. Whether or not the buds fell in 

 these varieties depended largely on the temperature, at lower tempera- 

 tures no fall occurring. Also, in cases where abscission of buds did 

 occur it was evident that something was actually impeding the pro- 

 cess ; none of the white substance formed by the isolated cells was seen 

 at the base of the pedicel and the buds had to be shaken or tapped 

 quite severely before they fell. 



The results of Experiment 12 and the various observations on the 

 induction of abscission by mechanical injury render it extremely 

 unlikely that checking the transpiration stream is ever a direct cause 

 of abscission. The few cases recorded above in which such a condition 

 seems to cause abscission can be better explained by the action of some 

 other factor than that of interference with transpiration. 



In connection with these experiments upon the effect of checking 

 transpiration the results of Lloyd and Balls on the effect of root 

 pruning, etc., in cotton must be mentioned. It was found that a pre- 

 mature shedding of flowers and young bolls followed root pruning 

 and further that, in general, there is a relation between boll-shedding 

 and the rise and fall of the water-table. Proof positive is not sup- 

 plied that root pruning causes fall of flowers by reducing the water 

 supply of the plant body, and any number of other factors may enter 

 in after such mutilation to bring about, in part at least, such a result. 

 Experiments reported in the present paper seem to leave no doubt 

 that, in Nicotiana at least, temperature is a more important factor in 

 controlling abscission than water supply. 



