Vererbung, Variation, Mutation. 159' 



The factor S affects only black pigmentation and does not produce any diffe- 

 rence in the appearance of red, at any rate that has as yet been identified. 

 White in plumage of pigeons is due to an indefinite number of f actors (W x , W 2 , 

 etc.) which inhibit the production of pigment in the areas which they influence. 

 Definite pattern s may result from the approach to a homozygous condition for 

 W factors which act on particular definite regions of the plumage. "Reversion" 

 to the wild blue Rock Pigeon type in domesticated pigeons is due simply to a 

 recurrence of the particular combination of factors which are present in C livia. 

 An extensive experiment on the inheritance of black and red showed an over- 

 production of red birds in F 2 , the ratio being practically 2 : 1 instead of 3 : 1. 

 This is not due to the absence of the homozygous dominant class as in yellow 

 mice. Possible explanations are offered but no definite conclusion is reached. 

 Different strains or family Hnes appear to have different tendencies as to the 

 ratios of blacks and reds they produce in F 2 . Lumping all of the results shows 

 still a slight excess of reds. The ratios of intense to dilute birds from hetero- 

 zygotes bred to other heterozygotes, or to dilute, approximate Mendelian ex- 

 pectation, that is 3 : 1 and 1:1, respectively. Various matings of the different 

 Colors give the results expected according to theory. A considerable number 

 of illustrative matings are presented. Pearl. 



388) Coliins, 0. N., A More Accurate Method of Comparing First- 

 Generation MaizeHybrids with Their Parents. In: Journ. Agr. Research, 

 Vol. HI, No. 1, S. 85—91, Oct. 1914. 



In this paper is described a method of measuring the effect of cfossing in 

 maize, apart from other factors that influence yield. To compare the behavior 

 of two varieties, which may be called A and B, with that of a hybrid between 

 them, two plants were selected in each variety, Al and A2 in the one variety 

 and Bl and B2 in the other variety. The following hand pollinations were 

 made: AlxA2, A2XB1, BIX B2, and J B2xil. The result is two hybrid 

 ears and one self-pollinated ear of each variety. It is believed that the mean 

 yield produced by seed from the two pure seed ears gives a fair measure of the 

 effects of hybridization. To secure the most accurate comparison of the yield of 

 the four ears, one seed from each of the ears was planted in each hill. The 

 different kinds were identified by their relative position in the hill. At harvest 

 time the seed produced by each plant was weighed and recorded separately. All 

 hüls that lacked one or more plants were excluded and the comparison confined 

 to hüls in which all four kinds were represented. The method of handling the 

 yields was to determine the mean yield of the four kinds in each hill and to 

 state the yield of each of the four plants as a percentage of the mean of the 

 hill in which it grew. The percentage standing of each kind in all the hüls was 

 then averaged to secure the final expression of the relative behavior of the 

 four kinds. 



The method is illustrated by an experiment in crossing two varieties of 

 sweet com in which it was found that the progeny from one hybrid ear yielded 

 nearly double that of the other hybrid ear involved in the experiment. To have 

 taken either ear alone would have led to entirely erroneous conclusions regard- 

 ing the increase secured as a result of crossing. The increase in yield due to 

 crossing as measured by the method here proposed was 31 per cent. Pearl. 



389) Smith, W. W., Color Inheritance in Swine. In: Amer. Breeder's 

 Mag, Vol. IV, No. 2, S, 113—123, 1913. 



