304 RAYMOND PKARL. 



English poultry artist Lucllow. and published in a plate facing 

 p. 20 of EntwisleV book. 



One of the most important and most baffling problems in 

 genetics today is the analysis of " pattern" inheritance. There is 

 definite and indubitable evidence that certain plumage patterns 

 in poultry behave as clean-cut unit characters, dependent on 

 gametic determiners or factors which act precisely like pigment 

 factors for example. Yet the gametic and ontogenetic mechan- 

 ism of pattern determination and development is most difficult 

 even to imagine. There certainly is great need for further 

 research in this field. Particularly it is important to see whether 

 definite patterns may be formed dc noi'o from crosses of birds 

 which bear no trace of the determiners of the patterns gametically. 



The case here under discussion illustrates the difficulties which 

 attend the getting of really critical evidence on this matter for 

 the barred color pattern. Merely to show that a black and white 

 bird mated together give barred offspring will not suffice. This 

 happens if one mates any bird carrying black pigment with a 

 \Yhite Plymouth Rock, but it is merely (and obviously) because 

 the White Rock carries the barred pattern factor as a cryptomere. 

 To get crucial evidence one must use black and white breeds (a) 

 in which there is no evidence of barred birds having been used 

 in the crosses from which the breeds were originated; (b) in 

 which there never occur barred "sports"; (c) in which barred 

 varieties of the breed are unknown; and (d) in which the white of 

 the white parent is a "recessive" and not a "dominant" white. 

 These criteria at once exclude from experiments on synthesi/ini: 

 the barred pattern from black X white crosses, if such experi- 

 ments are to be really critical, all Mediterranean breeds (so far at 

 least as these breeds are known to the writer). Further the >tock 

 used must be given a thorough preliminary test in Barred Rock 

 crosses to determine whether it docs or does not carry the B 

 factor. Experience indicates that it is difficult to settle this 

 point if the white of the white race belongs to the "dominant 

 white" category. There are, however, certain races of poultry 

 which seem to fulfil the requirements for a crucial test of the 

 fundamental question of the de iioro formation of the barred 



1 Loc. cit. 



