THE OXIDASES IN RELATION TO PIGMENTATION 255 



and it is found that the F 1 plants are pigmented, as both 

 and are present. 



Such F x plants produce gametes 00 and Oc; hence, 

 when self-fertilized, F 2 consists of 3 00 : 1 Oc namely, 

 3 reddish-stemmed plants : 1 green-stemmed. 



Now, although chromogen is the factor limiting the pro- 

 duction of anthocyan in a cell, the oxidases are in their 

 opinion part of the mechanism, as is further illustrated by 

 the fact that it is precisely those tissues which are rich in 

 oxidase in unpigmented varieties that are rich in anthocyan 

 in the pigmented. 



Further research showed that among the red-stemmed 

 there were two varieties dark red and reddish. These 

 differed in that the former contained the pigment in 

 epidermis, cortex, and stele; whereas in the latter it is con- 

 fined to the epidermis and adjacent cells. As the result 

 of crossing, it was seen that F x plants were reddish, and 

 F 2 consisted of 3 reddish : 1 dark-red stemmed. This 

 dominance of the light-coloured variety is evidently due to 

 the presence of an inhibitor sufficiently strong to suppress 

 pigment formation in the deeper tissues. 



With regard to the production of colour in flowers, the 

 results of genetic experiments revealed the presence of two 

 varieties of white flowers in Primula sinensis. These are 

 known as "recessive" and "dominant" whites. The 

 former evidently lack the factor for colour, for when crossed 

 with a coloured variety they yield a coloured F 15 which 

 when self -fertilized, gives 3 coloured : 1 white in the 

 F 2 generation. The dominant whites, however, yield 

 a white F x when similarly mated, and afford 3 white : 1 

 coloured in F 2 . Keeble and Armstrong have shown 

 that in the dominants an inhibitor of oxidase action is 

 present, whereas the recessives contain no such substance. 

 Again, in flaked or ever-sporting varieties of this plant 



