552 



HEREDITY 



neither parent dominating, and ia the second hybrid generation 

 the individuals are of various sizes, ranging from that of the 

 smaller to ^that of the larger parent (Figs. 4B0, 481 and 4^£). 

 At first such cases were considered striking exceptions to Men- 

 del's law. However, a more careful study has led to the view 

 that quantitative characters do mendelize but commonly depend 

 upon so many independent factors, each of which is responsible 



^.- •...-.. ._J 



Pig. 481. — Inheritance of length of ears in Corn. The ears Pi are eara 

 of the parent plants (Tom Thumb Pop Corn at the left and Purple Flint Corn 

 at the right) chosen to represent the average length of ears of parents. Notice 

 that the ear of the Fi generation is intermediate in length between the paren- 

 tal ears, while in the Fi generation, as shown by the ears at the left and right 

 of the Fi ear, the length of ears range from that of Tom Thumb Pop to that 

 of Purple Fhnt. After East. 



for a part of the character, that, although they do segregate and 

 combine according to Mendelism, they form so many kinds of 

 combinations and thus so many kinds of individuals occur in the 

 second generation of hybrids that it is difficult to detect mendel- 

 lian ratios. For example, in the case of crossing the taU and small 

 varieties of Com, it is assumed that the tall variety has a number 

 of factors for size that are not present in the small variety. Let 

 us suppose the large variety has four extra factors for size that 

 are not present in the small variety. These factors may be rep- 



