No. -199] A NEW MENDELIAN RATIO 447 



offspring of such plants are grown under favorable con- 

 ditions the latent characters are again rendered patent, 

 showing that the loss of external manifestation has had 

 no influence upon the allelomorphs themselves ; they were 

 present in the badly developed specimens, but were in- 

 visible because a sufficiently late stage of differentiation 

 was not attained to permit them to express themselves. 



Another striking case in which the latency of a Men- 

 delian character, perhaps due to fluctuation, has been 

 fully demonstrated, is in the cross between blue and 

 white Indian corn investigated by Lock. 11 The blue is, 

 in general, dominant over the white, but the white grains 

 are always in excess of expectation, sometimes more, 

 sometimes less ; subsequent breeding tests with the whites 

 show that a sufficient proportion of them are heterozy- 

 gous, instead of extracted recessives, to make up the 

 deficiency found in the number of blues in the preceding 

 generation. It is not impossible, as Lock suggests, that 

 further investigation of this case will discover some 

 other cause than fluctuation for the latency of the blue 

 aleurone layer in these white-grained heterozygotes. 



The classic case of so-called "double adaptation" in 

 Polygomnn amphibium which is pubescent in its terres- 

 trial form and glabrous when grown as an aquatic, and 

 other cases of the same kind, present illustrations of 

 latency due to fluctuation, instead of being due to the 

 presence of two antagonistic determinants whose activ- 

 ities are mutually exclusive as suggested by De Vries. 12 



The very common occurrence of latency due to fluctua- 

 tion must have an important bearing upon the signifi- 

 cance of cultural conditions for the production of varia- 

 tions. There has been much diversity of opinion on this 

 point, the general impression being that cultivation and 

 the removal of competition are very potent in inducing 



"De Vries, H. Species and Varieties, their origin by mutation, pp. 

 xviii + 847. 1905. Chicago : Open Court Pub. Co. See p. 430 et seq. 



"Lock, E. H. Plant Breeding in the Tropics. III. Experiments with 

 maize. Ann. Eoy. Bot. Gard. Peradeniya, 3, pt. 2, pp. 95-184, November, 

 1906. See pp. 144-163. 



