GABRIELLE L. C. HOWARD. 



As the parents in the cross Type 23 x Type 38 (Table XXIV) 

 are so similar as regards venation, no investigations on this 

 character were contemplated. A few measurements were 

 made, however, in the Fo as some other characters had given 

 curious results in this generation. The results obtained in 

 this generation afforded very striking evidence of the accuracy 

 of the method adopted, and so a few cultures were measured 

 in the Fg. Type 23 has a range of 70° to 80°, Type 38 of 60° to 

 75°, both therefore overlap. The plants in the Fg generation 

 had a range of 60° to 85°, the combined range of the parents. 

 In the Fg, cultures were found like both parents, i.e., 

 Nos. 213 and 6, some like the F2, Nos. Ill and 204 and others, 

 which indicate the possibility of another homozygotic combina- 

 tion with an average of 70°. 



7. THE LEAF SHAPE. 



The most difficult characters to investigate are those 

 connected with the shape of the leaf. The large number of forms, 

 all slightly different, with apparently endless modifications of the 

 individual parts, appear at first to defy analysis. A detailed 

 study of the existing forms and their behaviour on hybridization 

 shows that the number of characters is not so great as might be 

 supposed, although the factors composing such characters 

 are probably numerous. The form of a tobacco leaf can be 

 expressed by a determination of the following points : (1) 

 ratio length/breadth, (2) position of the greatest width, (3) 

 amount of indentation at the apex, (4) amount of indentation at 

 the base, (5) shape at the point of insertion, that is, whether 

 auriculate or not. According to the evidence which has accu- 

 mulated during these investigations all these characters are 

 inherited quite independently of one another. 



The influence of the ratio length/ breadth on the shape of 

 the leaf is obvious. The ratio depends on the two variable 

 characters, length and breadth. Apart from environmental 



