No. 531] THE GENOTYPE HYPOTHESIS 



165 



giving a 3 : 1 ratio, or as the complemental action of two 

 different units each allelomorphic to its absence, giving 

 9:3:3:1 ratios or modifications of them. Nillson-Ehle 6 

 and the writer, 7 however, have shown that several units 

 each allelomorphic to its own absence may be the determi- 

 nants of what appears to the eye as a single character. 

 In the above paper the writer suggested that if such 

 ratios as 15:1 and (>.'?: 1 — di-hybrid and tri-hybrid ratios, 

 respectively — were found in considerable numbers, then 

 higher ratios of this kind might account for the apparent 

 constancy of hybrids in characters that seemed to be con- 

 tinuous. For, if — as is quite probable — the additional 

 units increase the activity of the character in question, 

 and if there is no dominance, 8 it is quite evident that 

 hybrids may be intermediate between the two parents. 

 All the pure classes in a complex character of this kind 

 would indeed be difficult to isolate, but segregation could 

 be absolutely proved by a comparison of the variability 

 of the Fj and F 2 generations. 



Since writing the above paper I have obtained clear 

 evidence of 15 : 1 ratios in two other cases. The first is 

 a red pericarp color, the second is the condition of endo- 

 sperm in maize which gives dented seeds as distinct from 

 that which gives flinty seeds. There is even considerable 

 probability that higher ratios occur which affect the latter 

 character. In another paper 9 I have shown photo- 

 graphic evidence of size segregation in varieties of Xiro 

 tiana rustica and stated that similar evidence of segre- 

 gation of size character in maize had been obtained. The 

 following figures and tables show sufficient of the evi- 

 dence from the maize crosses to demonstrate conclusively 



•Nillson-Ehle, H., 1909, "Kreuzungsuntersuchungen an Hafer und 

 Weizen," Lunds Universitets Arsskrift, N. F., A fa. 2., Bd. 5, Nr. 2. 1-122. 



7 East, E. M., 1910, "A Meiulelinii Interpretation of Variation that is 

 Apparently Continuous, »> Amer. Nat., 44: 65-82. 



the average increase the manifestation of the character half as much as 



•East, E. M., 1910, "The Hole of Hybridization in Plant Breeding," 

 Pop. Sci. Mon., Oct., 1910, pp. 342-354. 



