330 



THE AMERICAN NATURALIST 



[Vol. LV 



^Ve found it necessary to use "Cuba" (U. C. B. G. 

 200/14),^ another white-flowering variety, in these 

 studies. Since there is the possibility just indicated of 

 the existence of genetically distinct white-flowering 

 varieties, it became necessary to determine the genetic 

 constitution of *'Cuba" with respect to the Rr and the 

 Pp pairs of allelomorphs. A number of crosses were 

 made, therefore, between "Cuba" and macrophylla as 

 the starting point for these determinations. In the ac- 

 count which follows H,,, = 7nacrophijlla ?X"Cuba" 

 and H,-5 = the reciprocal. In the season of 1919, 50 

 plants of FiHj,4 and 100 plants of F^K.^^ were grown. 

 They were all pink-flowering except that one plant pro- 

 duced a small white-flowering branch in an inflorescence 

 otherwise pink-flowering. This bud variant, one of the 

 few which we have observed in tobacco, will be taken up 

 in a subsequent report. The further data on these re- 

 ciprocal hybrids are listed in Table I. The F2 popula- 



19FlHl74P2?P 



2 populations 



l6FiH,s.. . 200,14^ 

 i9FiH,,.. . 



.6F,Hiw. . 15F,Hi7-,^ 

 Totals for back-crosse.'i 



