The Formation of the Anthocyan Pigments of Plants. 129 



lilac colour which, taken in conjunction with the previous observations, 

 indicates that benzidine facilitates the transference 6f oxygen from oxydase 

 to a-naphthol. 



In order to make clear the closeness of the analogy between the oxydase- 

 benzidine and oxydase-benzichne-methyl quinol reactions on the one hand and 

 those which lead to the production of the quinol colours — blue, red, and 

 magenta — of such a plant as P. sinensis, it is necessary to give a brief account 

 of the genetics of flower colour in this plant. 



The flowers of P. sinensis stand in a definite and constant relation with 

 one another. They form a series : recessive white, blue, red, magenta and 

 dominant white. The biochemical nature of the whites has been described in 

 an earlier communication (Part III). 



Of the coloured members of the series blue is recessive to both red and 

 magenta, and red, which is dominant to blue, is recessive to magenta. 



The Mendelian interpretation which fits the genetical facts is as follows : — 



The character for blue flower depends on the presence of a single 

 Mendelian factor. Bed flowers also contain this factor and they contain in 

 addition a factor for red which can produce its effect only in the presence of 

 the " blue " factor. Similarly magenta flowered plants contain a magenta 

 factor which when present together with the red and blue factors gives rise 

 to the magenta character. 



In the absence of the lower members of the series, colour is not produced 

 and the colour of any flower is an indication that the series of factors is 

 unbroken up to the factor for the colour character manifest in the flower. 



We have thus a striking parallel between the colour series in P. sinensis 

 and that which occurs with benzidine and methyl quinol. The closeness of 

 the parallel is indicated thus : — 



P. sinensis. Biochemical model. 



Oxydase. Oxydase. 



/ \ / \ 



Blue factor. + Red factor. Benzidine. + Methyl quinol. 



I Red. | [ Red. I 



Blue. Colourless. Blue. Colourless. 



The peculiar behaviour of the red factor, first in failing to induce colour 

 formation in the absence of the blue factor, and, second, in masking com- 

 pletely by a red pigment the activity of the blue factor, is to be accounted for 

 thus : — The red factor determines the formation of a specific substance — 

 perhaps of the nature of a phenol. That substance is not oxidised directly by 

 the oxydase of the flower, but in the presence of the " blue " factor this 

 specific substance receives oxygen from the blue pigment produced by the 



