334 



The Journal of Heredity 



linked, tlie <Jtlier a simple Mendelian 

 character. We have found some evi- 

 dence that the presence or absence of 

 a winter cycle in fowls that lay at all 

 during the winter'- follows the Men- 

 delian scheme. Since the influence of 

 the various modifying factors is so clear 

 cut, it is evident that egg production 

 is a character wholly unsuited for study- 

 ing the possibility of the modification 

 of tlie germinal representatives of a 

 character by selection. On the other 

 hand, it is a gcxDd example of a charac- 

 ter that varies continuously, but the 

 continuity of whose variability can be 

 shown to depend upon several modify- 

 ing factors. 



There is a ])oint of some general in- 

 terest regarding the genetic comix)sition 

 of any given flock. Hardy ('08)^ 

 showed that the proportions in which 

 a Mendelian character occurs tends to 

 remain constant provided no selection 

 is practiced. Fanciers often practice a 

 certain but indefinite amount of in- 

 breeding. Under such circumstances 

 there would be a tendency for the fe- 

 cundity factors to remain in about the 

 proix>rtions in which they started. We 

 may, therefore, expect to find ready- 



made flocks of high producers, true 

 mediocre producers, or even zero pro- 

 ducers as well as those containing the 

 several types. Thus, the original l>arred 

 IMymouth Rocks of the Maine Station 

 contained all three types, while the 

 Cornish contain only true mediocre and 

 zero producers. 



In spite of the fact that we have as 

 yet been unable to api)ly Pearl's theorv 

 of egg ])roduction boflily to our Rhode 

 Island Reds (although it may yet be 

 possible to use it after making some 

 modifications), there is no question but 

 that the ability to lay is inherited. a'< 

 shown by a better tgg production in 

 some families than in others. It is 

 clear also that some males produce off- 

 spring that on the whole make much 

 better records than those from other 

 males when the two groups of females 

 with which they are mated are veri- 

 similar in their winter egg production. 

 In one instance, the difference between 

 two sets of offspring by two males was 

 clearly due to a difference in maturity. 

 It seems clear, moreover, that some 

 of the internal factors, such as broodi- 

 ness and maturity, segregate indepen- 

 dently. 



APPENDIX 



Natural Crossing in Wheat 

 (See article on page 326) 



2 The absence of a winter cycle in this instance means continuous production through- 

 out the winter and spring, and not absence of egg production as in Pearl's Barred Plymouth 

 Rocks. 



' Hardy, G. H., Mendelian Proportions in a Mixed Population. Science, Vol. 28. 



