1918] Kendall: Abscission of Flowers and Fniifs in Solanaceac 387 



tioii to removing tiie anthers before anthesis. Various experiments 

 liad shown that such an operation on the flower does not induce 

 abscission or affect its normal physiological condition to any great 

 extent. 



F^ H154 is Nicotiana Tabacum vai". niacropJiylla (U. C. B. G. 

 22/07) X N. sylvestris (U. C. B. G. 69/07). F, H179 is N. Tabacum 

 "Cuba" (U. C. B. G. 200/14) X N. sijlvestris. F, H36 is .V. sijlvestris 

 X N. Tabacum var. angustifolia (U. C. G. B. 68/07). 



The results given in table 1 indicate, in the first place, that the 

 different species differ considerably in all the types of abscission 

 reaction times considered, and, in the second place, that on the aver- 

 age, application of a fertile pollen to the stigma tends to shorten 

 the time between anthesis and abscission of the corolla by two days. 

 The one apparent exception to this statement is Nicotiana suaveolens, 

 but in this case the i)ollinated flowers • fell five or six days later 

 than the corolla, indicating that growth of the pollen had not pro- 

 ceeded very far. Records on F^ H179 and N. sylvestris indicate that 

 sterile pollen does not have the same effect on abscission that fertile 

 pollen does. This would seem to show that here the effect of pollina- 

 tion upon the postfloration phenomena is not due, as Fitting (1909) 

 has found in orchids, to mere mechanical or chemical stimulation of 

 the stigma by the pollen. This much being certain, the question still 

 remains whether the results obtained depend upon fertilization or are 

 due to the growth of the pollen tubes down through the style. 



According to East (1915), working on self-sterility in Nicotiana 

 hybrids, the pollen tubes reach the ovary, in cases of cross-pollination, 

 three or four days after application of pollen to the stigma. Since in 

 all cases recorded above cross-pollination was carried on and since in 

 most cases the corolla was not thrown off until three or four days 

 after application of pollen to the stigma, it is possible that fertiliza- 

 tion is the important factor in shortening the time between anthesis 

 and abscission of the corolla. In N. quadrivalvi-s, however, the corolla 

 was thrown off within eighteen hours after pollination, whereas, when 

 pollination is prevented, the corolla may remain on the flower for 

 fifty-seven hours. If East's conclusions are correct, this would seem 

 to indicate that the shortening of the reaction time in abscission of 

 the corolla is due to some stimulation of the stjde by the pollen tubes 

 and not to fertilization. This conclusion, however, could be doubted 

 even here, because the style of N. quadriimlvis is very short, so that 

 the pollen tubes might reach the ovary in a much shorter time than is 



