No. 499] 



.1 .YAH' Mh'.XDELIA.X RATIO 



449 



seen in Lock's blue X white corn cross and doubtless in 

 very many other cases. 



It is probable that many discrepancies between actual 

 and theoretical ratios are due to some sort of latency. 

 This will generally he detected readily in subsequent gen- 

 erations, and no one should he hasty in declaring that a 

 character which is of the splitting kind is non-Mendel ian 

 until the various types of latency are considered which 

 may have taken part in modifying the ratios. ''Variable 

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

 gametes, and "alternating dominance" will all need to 

 be reconsidered and in some cases reinvestigated, before 

 they can have any secure standing as exceptions, amend- 

 ments or additions to the simple law of "purity of the 

 gametes" which is the essence of Mendelism. 



may be produced, without in any way affecting the funda- 

 mental principle of the purity of the gametes, their pro- 

 duction in equal numbers, and their union according to the 

 laws of chance, and wdiile the question of latency is not 

 involved in this case, it deserves to be mentioned in this 

 connection. Baur 13 has shown that in a variegated race 

 of Antirrhinum, the variegation belongs only to the hetero- 

 zygote. The extracted recessives are green and the ex- 

 tracted dominants fail altogether to appear, owing evi- 

 dently to the fact that the zygote so formed is inca- 

 pable of development, the ratio resulting from self- 

 fertilization of the heterozygotes being therefore 2:1. It 

 is conceivable that every degree of inefficiency of zygotes 

 formed by the union of two particular allelomorphs might 

 occur and thus quite various modifications of the expected 

 ratios be the result, when those ratios are determined by 

 a count of the successful zygotes. This cause for the 

 failure of the expected ratios is certainly of rare occur- 

 rence, but like questions of latency it can be demonstrated 



