270 



Gates. 



reacting substances are present in slightly different quantities in the 

 germ ceUs representing "presence" and "absence" of the given character. 

 In other words, the difference is quantitative, and not due to the pre- 

 sence or absence of any specific substance. I first expressed this view 

 in a consideration of the origin and peculiarities of 0. rubricalyx (Gates 

 1910 and 1911 b), and many subsequent facts have confirmed the 

 opinion there expressed. Several other investigators have recently 

 arrived at similar conclusions. 



We have seen that the ratios 3:1, 5:1, and 10 : i obtained with 

 the character R in the F, of crosses between grandiflora and rubri- 

 calyx, are incompatible with the Mendelian presence-absence hypo- 

 thesis, but that the complex results fall into hne with the view that 

 R and r are quantitatively different from each other, and that grandi- 

 flora inhibits anthocyanin production according to the proportion in 

 which it is represented in the parents of the cross. The most careful 

 observation and study shows that the red pigmentation-character 

 R is, in the last analysis, inherited in quantitative fashion. Super- 

 ficially, if the presence of a red or a green hypanthium be taken as 

 the criterion of presence or absence of R, it is possible to classify very 

 nearly all individuals into one or other of these two sharp categories. 

 But more critical examination shows that a marked increase in the 

 quantity of pigment is accompanied by a definite extension of the 

 pigmentation, so that the hypanthia are red and not green. Why 

 this should be so is an unsolved problem in morphogenesis, though 

 it would appear that the sharpness of the difference between R and r 

 is conditioned by something in the manner of development of the 

 hypanthium rudiment (i). The mere quantity of pigment in the cells 

 of the organism shows no such sharp break, and is intermediate in 

 crosses. Just as a lake may overflow and quickly irrigate a previously 

 dry basin at a lower level, owing to a sudden influx of water after a 

 downpour, so the original rubricalyx mutant from rubrinervis had its 

 hypanthia suffused with anthocyanin as they developed, owing to 

 the much greater pigment-production of the cells in all parts of the 

 organism. The latter fact was due fundamentally to a quantitative 

 change in the chemical activities of some part of one of the original 

 germ cells. 



(^) In this connection it may be recalled that the hj-panthium is a characteristic 

 organ of the genus Oenothera, though it varies greatly in size and shape in difierent 

 species; and that it may have originated suddenly through a mutation. 



