230 



MULTIPLE FACTORS 



Two varieties of tobacco, Nicotiana alata grandi- 

 flora and N. forgetiana, were crossed by East. They 

 differ mainly in the size and color of the flower. The 

 corolla is three times as long in one as in the other 

 variety, as seen in Fig. 55. In the table, page 

 185, the lengths of the corolla in the two varieties, 



Fig. 55. — At the left a flower of Nicotiana alata grandiflora; at the 

 right a flower of N. forgetiana; in the middle the Fi hybrid. (After 



East.) 



in the Fi, and in the F2 plants are given. The table 

 shows the small variability of the parents. The Fi 

 generation is intermediate in length and also shows 

 little variability, while the F2 generation gives no 

 definite ratios but exhibits great variability (Fig. 56), 

 and overlaps the two grandparental types, although 

 only a few flowers in F2 are identical in size with those 

 of each of the two grandparental types. These 

 results are those expected if the two parent varieties 



