88 INHERITANCE IN POULTRY. 



No. 386 9 ; for this hybrid has a high nostril and a pair of papillae like 

 the Houdan mother, both of which characters are recessive. Out of 41 in- 

 dividuals No. 386 is the only one that exhibits them. It appears, then, that 

 " prepotency " in its modern sense can not be neglected. 



HYBRID FORMS. 



It sometimes happens when two dissimilar characteristics are crossed that 

 neither appears in the offspring, but they are replaced by a new character. 

 This fact has been long known. Mendel obtained such hybrid forms (cf. t 

 Correns, 1905, p. 232). Several cases are cited by Focke (1881, pp. 473, 474). 

 He refers particularly to the blue hybrid of the white Datura Jcrox crossed 

 with the likewise white D. laevis and D. strammonium Bertolonii. 



As a result of more recent work it appears probable that hybrid forms are 

 of two kinds. First, such as are atavistic or due to the becoming patent of 

 a latent characteristic ; * and, second, such as are due to a particulate inher- 

 itance of the two characteristics crossed. In the latter case all that is novel 

 in the hybrid is the replacement of either single character by a combination 

 of characteristics. 



Atavistic hybrid forms have been carefully investigated of late, especially 

 by Correns (1902) and Cuenot (1903), who have applied a method of inter- 

 pretation to particular cases. When albino mice are crossed inter sc they 

 produce only albinos. But if such an albino is crossed with a pigmented 

 (e . g. , a black) mouse its latent pigment appears and the offspring may be 

 all gray, or perhaps yellow and gray or yellow and black. The same holds 

 exactly true for albino rabbits, as Hurst (1905, pp. 306-310) has shown. 

 Cuenot' s interpretation depends on the principle that pigments result from 

 the action of an oxidizing diastase (tryosinase) upon a chromogenic sub- 

 stance. Both of these elements are present in a pigmented mouse, but he 

 assumes the chromogenic substance alone is present in the albino. The sperm 

 from the pigmented male brings to the egg of an albino the diastase necessary 

 to the production of pigment in the offspring. Correns (1905) finds that 

 the hybrid of Mirabilis jalapa alba (white flowers) and M. jalapa gilva (yel- 

 low flowers) has rose-colored flowers that are, moreover, striped with red. 

 His experiments lead to the conclusion that the alba variety forms no pig- 

 ment, but does produce a pigment-changing (reddening) enzyme. The^-zYzvz 

 variety forms pigment, but not the reddening enzyme. When alba sperm 

 unites with the gilva egg the pigment of the latter, under the influence of 

 the reddening enzyme, becomes rose. Similarly with striping. There is 

 evidence that this is only partly latent in alba and completely latent in gilva. 

 Now if we assume a factor that permits the development of the striping 

 determinant to be active in gilva but to be latent in alba, the imperfect 



*Tschermak (1904, p. 95) would add as another kind that in which an originally patent 

 character becomes latent. 



