494 Universitij of California Puhlicatious in Botany ['^'ol. o 



Although intermediaey of the heterozygote appears to be the normal 

 thing in these leaf shape contrasts, it is proper to state that this inter- 

 mediaey may depend to some extent upon the effect of modifying 

 factors rather than upon the heterozygous conditon of a pair of allelo- 

 morphs. Thus the intermediate conditon between stenophylla and 

 AURICULATA is met with in populations which do not contain auricu- 

 LATA segregation products. There are so many modifying factors in 

 this series of investigations that it is probably impossible for us to 

 declare definitely that in any one instance our observed segregation 

 was wholly the result of segregation of one pair of allelomorphs. 

 Further investigations are in progress, the purpose of which is to 

 isolate and evaluate, if possible, certain of these subsidiary factors. 

 For the present we can only state our certain knowledge of their 

 existence, and our belief as to their various effects. 



IV. CALYCINA-YIRGINICA SERIES 



The calycina-virginica series of hybrids and derivatives has received 

 much less attention than has been given to the previous series ; partly 

 because the differences between the parents are less striking and the 

 diversity of segregation products was not so great. Two hybridizations 

 were made : H^g which had calycina for the female and virginica for 

 the male parent and Hoq which was the reciprocal cross. 



1. PAKENTS OF THE CALYCINA-VIRGINICA SERIES 



Elsewhere Setchell has given descriptions of calycina and virginica 

 ("Maryland"). Like angustifolia and macropJiylla, these two varie- 

 ties possess distinct sets of characters which set them apart from the 

 other Tabacum varieties that have been grown in the University of 

 California Botanical Garden. 



Calycina is represented in our cultures by a variety, U. C. B. G. 

 110/05, which was originally received from the Botanical Gardens of 

 Cambridge University. The figure previously published (cf. Setchell, 

 loc. cit., pi. 4) well represents the general habit and type of the plant. 

 The particular features of the characteristic teratological flower of 

 calycina are better shown in plate 79, in which the leaf shape is also 

 illustrated in more characteristic fashion. For illustrations of some 

 of the variations which occur in the expression of the split hose-in-hose 

 flowers the reader is referred to Goodspeed and Clausen, 1917, plate 45. 

 The legends to the two figures of this plate should be reversed as indi- 

 cated in the references to the plate in the text of this earlier article. 



