98 Comparison between [cii. 



The Case of Antirrhinum {Snapdragon). 



The experiments of Miss Wheldale (303) on Antir- 

 rhinum show that in that plant the appearance of the red 

 and magenta flower-colours is similarly dependent on the 

 presence of two complementary factors. In one respect, 

 however, this case differs from those which we have been 

 considering ; for whereas in them either of the two colour- 

 factors, spoken of as C and R, might be present in a truly 

 white-flowered plant, it appears that in Antirrhimi77t one of 

 the two factors produces either a bright yellow or a very pale 

 *^ ivory " yellow in the flowers. The other complementary 

 factor may be present in actual whites. Hence magentas 

 or reds may be produced by the cross between white and 

 yellow, or white and ivory, but hitherto crosses between 

 actual whites have not given coloured offspring. If in the 

 Sweet Pea for instance the presence of C caused the flowers 

 to be ivory instead of white the case would be like that of 

 Antirrhinum,. At first sight it might be supposed that the 

 phenomenon seen mMatthiola (Stocks), where white x cream 

 gives F^ with anthocyan colours, was more strictly parallel, 

 but in the Stock the cream is a plastid-colour, whereas in 

 Antirrhinum the ivory is a true sap-colour. 



It is a noticeable and rather unexpected feature in the 

 case of Antirrhinum that the pale ivory is due to a factor 

 epistatic on the bright yellow. The ivory is so pale that it 

 might on casual examination be described as white ; never 

 theless it is definitely and completely dominant to the bright 

 yellow type. 



Ivory crossed with white gives F^ magenta-red but 

 yellow crossed with the same white gives F^ crimson-red. 

 The distinction between the two kinds of red is due to the 

 factor which turns bright yellow into ivory. 



A comparison between the Sweet Peas or Stocks on the 

 one hand and Antirrhinum on the other, may be represented 

 in tabular form. Using a terminology applicable to both 

 cases let us designate the factors thus^ : 



Presence and absence of the ** ferment." F, f. 



„ „ „ „ "Chromogen." C, c. 



„ ,, ,, „ Epistatic factor. E, e, 



* In the previous discussion of the Sweet Pea the factors 7^ and E are 

 designated R and B respectively. 



