Inheritance in the Higher Plants 99 



may be scraped off to show the color of the true seed 

 which may be either yellow or white. In most cases, 

 however, the relations are physiological and the hypostatic 

 character can be demonstrated only by crossing. P'or 

 example, the maize with purple aleurone cells carries also 

 a factor for red aleurone cells which can be demonstrated 

 only by crossing it with a variety in which the purple factor 

 is absent. There is produced an F^ generation with a ratio 

 of 27 puq3les : 9 reds : 28 whites. 



This statement may appear to be a direct contradiction 

 of the interpretation of the inheritance of purple aleurone 

 color that has just been given. In reality it is merely 

 another illustration of the fact that one can never know 

 definitely the factors involved in producing a character, for 

 he can never feel assured that the parents involved in the 

 cross have differed in all the factors that affect its develop- 

 ment. When the purple was crossed with the white and a 

 ratio of 9 purples : 7 whites obtained in the F, generation, 

 it was proper to interpret the purple parent as P P C C 

 and the non-purple parent a.s p p c c. But when the purple 

 is crossed with another non-purple and a ratio of 2 7 purples : 

 9 reds : 28 whites is obtained in the F^ generation, it is clear 

 that a different interpretation is necessary. The purple 

 parent has the formula P P R RC C and the white parent 

 the formula p p r r c c. The zygotic formula of a pure red 

 seed is RRC C and of a pure purple seed is P P RRC C, 

 but a seed with the formula P P C C is white. In other 

 words, the factor P produces the visible purple color only 

 in the presence of factors C and R. The purple has always 

 the constitution P P RRC C ; when it is crossed with whites 

 having the characters P P R Re c or P P r r C C , a ratio 

 of 3 purples : i white is obtained in F^; when it is crossed 



