1918] Kc'Hckill : Abscission of Flowers and Fruits in Solanaceae 359 



(1916&) states that under field conditions the responses to all kinds 

 of stimuli conducive to abscission become evident within ten days, 

 with the maximum frequency below six days. 



The actual time involved in the process of abscission (abscission 

 time) has received even less attention than the problems discussed 

 above. Fitting (1911) states that abscission time may occasionally 

 be very short, forty-five seconds to five minutes in the petals of Ver- 

 hascum and thirty seconds to six minutes in Geranium. Lloyd (1914a 

 and 1916&) finds abscission after injury of the small cotton-boll taking- 

 place within four hours, the length of time depending somewhat on 

 the age of the boll. In a previous paper (Goodspeed and Kendall, 

 1916) a general estimate of the abscission time was given and it was 

 stated that normal abscission due to lack of fertilization takes place 

 in Nicotiana hybrids in four to eight hours and premature abscission 

 in one to four hours. 



5. Experimental Induction of Abscission 



According to Hannig and Loewi, abscission may be induced in 

 two different waj's. First by abnormal external conditions ("spon- 

 taneous" or premature abscission) and second by normal internal 

 conditions at the normal time ("automatic" or normal abscission). 

 We shall consider in the following summary of the literature onlj' 

 two aspects of induction of the first type. 



a. INDUCTION BY NAECOTIC VAPOES 



Hannig (1913) reports a comparative stud}- of the behavior of 

 cut sprigs of different species of plants when subjected to laboratory 

 air and to illuminating gas. He notes the fact that under either of 

 the above conditions all the flowers and occasionally a few small 

 shoots are abscissed. He finds, however, that not all the species in a 

 given famil}' behave similarly in response to these conditions. We 

 are particularly interested in the Solanaceae and we may note that 

 this family contained more species that detached their flowers in 

 illuminating gas than ^x\y other of the families investigated b}^ Han- 

 nig. According to Fitting (1911), narcotic vapors such as tobacco 

 smoke, carbon dioxide, ether, chloroform or illuminating gas fre- 

 quently cause premature abscission of the corolla. He notices, how- 

 ever, that ammonia or turpentine vapors fail to cause abscission. 

 Brown and Escomb (1902) make the statement that Nicotiana, Cu- 

 curhitn, and Fiichsiu shed flowers and buds in air containing ()nl\- 

 0.114 per cent carbon dioxide. 



