Xo. 499] 



A NEW MENDEL1AN RATIO 



451 



which hides the presence of a wholly distinct brown allel- 

 omorph, and a dark orange bean which carries invisibly 

 a light yellow allelomorph. This condition gives rise 

 in one series of crosses to the ratio, 12 : 3 : 1. Properly 

 the term " dominance ' ' should be limited to the relation 

 between any positive characteristic and its own absence. 

 Whenever one positive character seems to dominate 

 another positive character, the latter is latent by hypo- 

 stasis in the individual possessing the former. 



(d) Latency due to fluctuation, a very frequent phe- 

 nomenon in which characteristics disappear under con- 

 ditions of poor nutrition, etc. Cultivation under favor- 

 able conditions makes such characteristics patent and this 

 fact may account in part for the general impression that 

 cultivation induces variation. Cases of 1 'double adapta- 

 tion" are examples of this type of latency. 



Many discrepancies between theoretical and empirical 

 inheritance-ratios are due to latency, and care should be 

 taken to investigate the possible latencies which may be 

 present before declaring that a character is non-Men- 

 delian, because of a discrepant ratio. " Variable 

 potency," "contamination" or "impurity" of the 

 gametes, and "alternating dominance" which have been 

 proposed to account for the appearance of various novel- 

 ties, or of deviations from expected ratios, can have no 

 secure standing until the question of latency in the sense 

 of invisibility has been taken into account. 



A modification of expected ratios may rarely result 

 also from the failure of certain allelomorphs to make 

 vigorous zygotes when joined together in certain com- 

 binations. 



