358 Umversity of California PiiMioations in Botany [Vol.5 



He finds no cell divisions preceding or accompanying abscission. The 

 process in premature abscission he finds differing in no way from 

 that in normal abscission after fertilization. These conditions, he 

 states, correspond more or less to those which he finds in the pedicel 

 during flower-fall. 



4. Time of Abscission 



The time elapsing between anthesis and flower-fall in partially 

 sterile F^ species hybrids of Nicotiana and between emasculation at 

 anthesis and fall in the case of their corresponding parents is dis- 

 cussed in a previous paper (Goodspeed and Kendall, 1916). It was 

 there stated that the average time is about nineteen days in F^ H154, 

 seven in F^ H179, five in .Y. Tahacum var. macrophijlla, and thirteen 

 in N. sylvestris. When we turn to the question of the reaction time 

 in premature abscission occurring before the normal time as the result 

 of sudden changes in external environmental conditions, we find that 

 this subject has received only slight attention. According to Lloyd 

 (1914a), the cotton "square" falls in one to twenty-two days after 

 the weevil lays its eggs, the average time being eight days. In one 

 experiment in which the ovary was cut transversely, Lloyd was able 

 to cause one hundred per cent of the young bolls to fall in forty-eight 

 hours and ninety per cent in twenty-four hours. Larger bolls take a 

 longer time to respond to injury than do smaller ones, as a result of 

 the development of the pedicel to a condition in which abscission 

 meets greater resistance. Cotton ' ' sqviares, ' ' he finds, take a longer time 

 to respond than young bolls, the former shedding thirty-five to sixty 

 per cent in thirty-six hours and the latter forty to seventy per cent in 

 forty-eight hours. On the other hand, he obtains no evidence (1916&) 

 that the reaction times are any shorter in small buds than in larger 

 ones. The reaction times in cases where the injury is performed in the 

 evening seem to be shorter by about twelve hours than in cases where 

 the injury is performed in the morning. This difference he ascribes 

 to the increase in turgidity which takes place during the night and 

 which serves to hasten the reaction. Very severe injuries to the ovary, 

 he finds, cause fall of young bolls quicker than less severe injuries. 

 Injuries which are less severe than those mentioned above and per- 

 formed so as to imitate the injury inflicted on the ovary by insect 

 larvae caused shedding in three to six days, with most of the fall 

 occurring on the fifth day. Summing up his entire results, Lloyd 



