514 University of California Publications in Botany [Vol. 5 



of investigations with other forms, specific mention of which is un- 

 necessary. 



The general features of inheritance in Tahacum varietal crosses 

 are plain enough. The results of our investigations in this connection 

 agree throughout with the conclusions which Miss Howard drew from 

 her studies. When we are dealing with complex differences, the F^ 

 is commonly intermediate in character expression between the two 

 parents. Not only is this true as respects the F^ plant as a whole but 

 it is also true for individual characters. The F, commonly consists 

 of a varied assemblage of forms covering the range between the two 

 parents, or even not uncommonly presenting products not included 

 in the range between the two parents. So many and of such variety 

 are the forms obtained that accurate classification is entirely out of 

 the question. But in Fg and in subsequent generations segregation, 

 even for characters commonly regarded as quantitative, sometimes 

 occurs in distinct discontinuous classes in marked contrast to the inter- 

 grading series of forms obtained in F,. This is shown particularly 

 well in our analysis of leaf base factors, for in this case we have been 

 able to adopt a qualitative mode of attack on one of the features w^hich 

 contributes to leaf shape. If such an analysis proves successful in 

 one instance, there seems to be little reason why it should not be ex- 

 tended to others. There is, therefore, additional evidence in this suc- 

 cessful application of the mode of qualitative analysis to quantitative 

 characters in support of the oft repeated contentions of East (1913), 

 Hayes (1912), Hayes, East, and Beinhart (1913), Miss Howard 

 (1913), and others that fundamentally the same mode of inheritance 

 holds for quantitative characters in tobacco as for qualitative ones. 

 The distinction between the two classes of characters is purely an 

 artificial one erected for the purpose of convenience in formal treat- 

 ment, and at most depending merely upon an increase in complexity 

 of the factor relations involved and on the greater fluctuation of the 

 characters in response to environmental differences. 



The question remains to be discussed whether semiquantitative 

 characters admit of a qualitative mode of analysis, and if so, how? 

 Miss Howard (1913) as a result of her extensive studies of inheritance 

 in Indian tobaccos concludes that the easiest way to determine the 

 principles underlying inheritance in these forms is to establish as 

 many extracted homozygous intermediate forms as possible. The estab- 

 lishment of such forms in themselves, however, is only a step in the 

 Mendelian anah'sis of the differences. Such forms are, as might have 

 been expected on theoretical grounds alone, less different from one 



