54 Heredity and Eugenics 



fingers behaves as a simple dominant unit-character. A 

 curious affection of the nervous system producing the 

 waltzing condition of Japanese mice, behaves as a recessive 

 unit-character in crosses with the normal condition. 



Is all inheritance unit-character inheritance? This 

 question cannot at present be answered fully, but many 

 facts indicate that it is. A large class of seemingly uncon- 

 formable cases which presented the greatest obstacle to such 

 a view has recently been brought into line with the unit- 

 character hypothesis. I refer to cases of blending inherit- 

 ance, in which the offspring are intermediate between the 

 parents, and this intermediate condition persists into the 

 next generation. 



Size and skeletal proportions are inherited apparently 

 in this fashion. It is possible, however, that even in such 

 cases unit-character segregations may really occur, though 

 their presence is obscured because dominance does not occur. 

 For in plants such size segregations have been observed 

 recently by my colleague Dr. East and by others. 



A single illustration will suffice. When varieties of maize 

 (or Indian corn) are crossed which differ in size of ear, 

 the hybrid plants bear ears of intermediate size but not 

 more variable than the more variable parent. The second 

 generation offspring, however, are extremely variable, 

 ranging in size from that of the smaller parent variety to 

 that of the larger. 



The peculiarity of what we have called blending 

 inheritance lies partly in the entire absence of dominance. 

 In blending inheritance a unit-character represented once 

 in the fertilized egg has only half as much effect as one rep- 

 resented twice. In color inheritance, usually, but not always, 

 a single dose of a unit-character is as effective as a double 



