58 STUDIES IN INDIAN TOBACCOS. 



rise to a culture which appeared absolutely uniform in the field. 

 The average height of the culture was 50.8 cm., much less than 

 that of Type 35, and the limits of variation (35 to 65 cm.) do 

 not overlap those of Type 35. The individual heights of the 

 plants, if graphically represented, give a curve which resembles 

 greatly the ordinar}'' frequency curve of a uniform culture. 

 This fact, combined with the appearance of the culture in the 

 field and the small range of its variation, makes it probable that 

 251 represents a culture constant as regards height. We have 

 thus the formation in the Fg of a new form much shorter than 

 either parent. The factor or combination of factors which 

 is represented by this average height of about 50 cm. may be 

 present in both parents, or only partly in both, but the fact that 

 this combination has been isolated shows that the height of 

 Type 16 cannot be composed of small factors superposed on those 

 possessed by Type 35. Even if we suppose that the combination 

 of factors denoted by a height of 50 cm. is common to both 

 parents, all the factors which go to form the excess of height 

 over 50 cm. in Type 35 and Type 16 must be different. This 

 gives the explanation of the very tall plants in the F^ and F^ 

 generations. Since so large a proportion of the height in the 

 parents is due to different gametes, the combined effect of such 

 gametes would be additive. 



There is no definite evidence as to the number of the 

 factors involved, but from the appearance of some of 

 the Fg cultures they would seem to be few in number. 

 Culture 190 is also probably uniform and a reproduction of 

 Type 16, the mean height in the one case being 102.1 cm., in the 

 other 106.3 cm. The range of variation is greater, but this 

 may be due to the larger number of plants measured. From 

 their appearance in the field and the curves given by their height 

 it is probable that the cultures 142 and 200 are not uniform, 

 but represent heterozygotes between two nearly allied combina- 

 tions. After 251, the most interesting culture is ^202. Here 

 we have a distinct break between the tall and the short plants. 



