106 STUDIES IN INDIAN TOBACCOS. 



have been re-isolated in the Fg and F4 generations and also 

 constant forms with intermediate venation. Many of the 

 factors involved have a very small external effect. 



13. The shape of the leaf in N. tdbacum may be defined by 

 the ratio length/ breadth, position of the greatest width, amount 

 of indentation of the apex, amount of indentation of the base, 

 nature of the insertion, whether auriculate or not. All these 

 characters can be inherited independently of one another. By 

 the hybridization of two forms, in Avhich the indentation factors 

 of the base differ, " petiolate " forms which at once breed true, 

 are produced by the combined action of the factors. All 

 " petiolate " leaves in this species are probably sessile leaves 

 with deep indentations. 



14. The irregularities of the surface of the leaves depend 

 probably on several factors. The undulation of the margin 

 in the particular case investigated proved to be due to a single 

 factor which is inherited independently of the factors concerned 

 in the surface of the leaf. 



15. Measurements of the size of the corolla show that this 

 organ resembles the leaves in its mode of inheritance. 



From the above results the following general conclusions may 

 be drawn : — The data obtained by a study of the characters of 

 N. tabacum show that there is no inherent difference in the mode 

 of inheritance of ordinary qualitative characters (such as the 

 colour of the corolla) and of those characters connected with the 

 size of the organs which are subject to fluctuating variability. 

 All the results obtained can be explained by the Mendel ian 

 assumption of segregation of characters, combined ^\•ith the 

 hypothesis that in connection with each character a large 

 number of factors exist, each of which can be inherited indepen- 

 dently. This conclusion is supported by the great range of 

 variation in the F2 generation, the formation of extreme forms 

 in this generation far outside the limits of the parents, the differ- 



