No.5S5] MODIFICATION OF CHARACTERS. 565 



crosses have already been published (Gates, 1914, p. 244 

 and 1915a, p. 257) and need only be summarized here, to 

 emphasize their significance. In the publications cited 

 I had not yet recognized that the occurrence of 15 : 1 ratios 

 in later generations of rubricalyx is significant as indi- 

 cating that in such families the duplicate condition for R 

 had been reached, even although other ratios such as 

 5 : 1 occur as well. 



The F 2 generation of the crosses between rubricalyx 

 and grandiflora contained 2,794 plants, in 20 of which the 

 red bud-character R showed decided modification so as to 

 be more or less intermediate between the two parents. 

 Since each plant in bloom produces scores of buds simul- 

 taneously, and hundreds during the season, there is ample 

 material for determining the exact degree of modification 

 or development of the character in every individual. As 

 will be seen from the original records, the 20 plants in 

 which the color pattern was more or less modified were 

 not all alike but formed a series, some being nearer the 

 normal R than others. In most other F 2 plants sharp 

 segregation took place, the buds being entirely either R 

 or r without the slightest doubt in classification. In addi- 

 tion to the 20 plants above mentioned, there were, how- 

 ever, a certain number in which the character R was more 

 or less underdeveloped, so that it was impossible to be 

 certain whether they represented mere fluctuations or real 

 modifications of the character. 



The crucial test of modification is supplied by the F s 

 generation. Two of these last-mentioned intermediate 

 plants self-pollinated yielded offspring like themselves, 

 without any tendency to segregate into the R and r types. 

 These families numbered, respectively, 283 and 20 plants, 

 so that in the former case at least any tendency to segre- 

 gation could not fail to be observed. The buds of these 

 plants were intermediate, the pigmentation was pale and 

 was never fully developed on the hypanthium as is the 

 case in rubricalyx. The whole population was then inter- 

 mediate like the parent. 



