PLANT HYBRIDIZATION BEFORE MENDEL 235 



mediate, and the crossing of white, black, and fawn-colored an- 

 gora rabbits, in which the colors are separately inherited, and not 

 combined in the same animal. The non-intermediate character of 

 the inheritance in the case of turnspit dogs and ancon sheep is 

 referred to, as is also the inheritance in the case of tailless, horn- 

 less breeds. Similar results in the case of stocks, toad-flax, and 

 sweet peas are cited, (ic, 2:68.) 



Darwin (ic, 2:44-45; 68-69), ^^ discussing what he called 

 "prepotency," is dealing in very many cases with that which we 

 now recognize as simple dominance. For example, in the crossing 

 of snap-dragons Darwin found that when the normal or irregular- 

 flowered (zygomorphic) type is crossed reciprocally with the pe- 

 loric or regular-flowered (actinomorphic) type, the former prevails 

 in the first generation to the exclusion of the latter. The 127 hy- 

 brid plants, self-fertilized, yielded in the second generation irreg- 

 ular to regular plants in the ratio of 88 to 37. This is evidently 

 an approximation to the 3:1 ratio, its defectiveness being un- 

 doubtedly due to the limited numbers. 



Darwin, however, regards it simply as a 



". . . good instance of the wide difference between the inheritance of a 

 character and the power of transmitting it to crossed offspring." (ic. 

 2:45.) 



Darwin was thus quite unable, with the information then 

 available, to frame a satisfactory explanation for the various 

 phenomena passing under the name of "prepotency." 



He makes one remark relative to prepotency, however, which 

 slightly grazes the recent presence-and-absence theory of Men- 

 delian inheritance. 



"We can seldom tell what makes one race or species prepotent over 

 another; but it sometimes depends on the same character being present 

 and visible in one parent, and latent or potentially present in the other." 

 (ic, 2:58.) 



The fact that certain characters are bound up with sex, or 

 "sex-linked," did not escape Darwin's observation. He alludes to 

 cases where a son does not inherit a character directly from his 

 father, or transmit it directly to his son, but receives it by trans- 

 mission from a mother who does not show it herself, and where 

 he transmits it in turn through the medium of a daughter, who 

 also does not show the character, but who acts as a carrier. 



