294 University of California Publications in Botany [Vol.5 



of flowers and fruits on the F^ species of hybrids and have given 

 further evidence concerning the relation between successful pollination 

 and fertilization on the one hand and abscission of flowers and fruits 

 on the other. The general problem of abscission in the Solanaceae 

 with particular reference to the genus Nicotiana is being investigated 

 by one of us and will be the subject of a more extended discussion 

 later on. 



AYe have first to consider the length of time intervening between 

 anthesis and abscission. In the case of protected flowers of the F^ 

 species hybrids this period is subject to rather extensive variation 

 (cf. Goodspeed, 1913). The following table indicates the results of 

 a number of experiments in which tagged flowers were carefully ob- 

 served from anthesis to fall. Although the hybrid flowers when pro- 

 tected fall as a result of unsuccessful pollination, the figures given in 

 the following table are based upon experiments in which botli hybrid 

 and parental flowers were castrated just prior to anthesis. The influ- 

 ence of slight mutilations of the flowers in making the castrations is 

 thus the same in all eases. F^ HI 54 is N. Tabacum var. macrophylla 

 (U. C. B. G. 22/07) X N. sylvestns (U. C. B. B. 69/07) and F, H179 

 is iV. Tabacum "Cuba" (U. C. B. G. 200/14) X N. sylvestris. 



Number of Days Eetweex Axthesis and Abscission, Average 



F, H154 19 



F, H179 7 



22/07 6 



69/07 13 



(200/14; cf. Goo<lspee<l, 191.5) 



The range for individual plants and their different flowers was 

 considerably greater. For example, in the case of Fj 11154 seven 

 different plants gave averages between 9 and 28 days, while the indi- 

 vidual flovrers on these plants showed variations in the time between 

 anthesis and abscission of from 6 to 33 days. The statement has been 

 made in a recent paper (Goodspeed and Clausen, 1916) that F^ H179 

 holds its flowers in remarkable fashion despite the fact that its pollen 

 is as non-functional as in the case of the other Tabacum-sylvestris 

 hybrids. It may thus seem strange that we list this hybrid with the 

 others in which abscission of almost all flowers and fruits is the rule. 

 The point here involved demonstrates to what extent the physiological 

 condition of the plant enters in to effect the abscission problem. Fj 

 H179 was first grown this past season (1915) and the plants from 



