156 On the Formation of Anthocj/anin 



equilibrium position is such that very little or no free chromogen is 

 present in the tissues subject to the variation : in the variety the 

 equilibrium position is possibly one of complete hydrolysis and the 

 tissue as a result becomes considerably pigmented. 



In the second place, there are anthocyanic species in which the 

 type has coloured flowers, and has given rise to a large number of 

 derivative varieties. Many of these have been fully described in Men- 

 delian literature, and several classes of varieties can be recognized 

 which are applicable to a number of different species. 



The main classes can be distinguished as : — 



I. The blue or purple anthocyanic class. 



II. The red anthocyanic class. 



III. The albino or non-anthocyanic class. 



Both I. and II. may in many cases exist in sub-classes common to 

 both; i.e. 



(a) The tinged class. 



(6) The pale class. 



(c) The deep class. 



There is no further evidence in the present paper beyond that 

 which I have previously given(20) as to the nature of the factors, the 

 absence of which causes loss of blueing power and albinism respectively. 

 They are in all probability oxidising enzymes, though I am by no 

 means unwilling to admit that blueing may in some cases, considering 

 the great number of possibilities in plant-metabolism, be due to 

 alkalinity of the cell-sap brought about by some definite enzyme 

 action. I am uncertain as to the nature of the factor, the absence of 

 which causes the tingeing. 



I. (b) constitutes the type in many species and deeper varieties of 

 both red and blue classes, i.e. I. (c) and II. (c) are known. They are 

 recessive to the type and are due to the loss of some factor. It now 

 seems probable that this factor is not a partial inhibitor or limiting 

 factor of a reductase nature such as I have suggested, but a controlling 

 enzyme, i.e. one which synthesises and hydrolyses the glucoside. Whereas 

 loss of this enzyme may give rise to coloured varieties when the type is 

 merely tinged and quite unpigmented, when the type is already 

 coloured the loss deepens the colour by increasing the amount of 

 pigment formed. 



Sometimes the loss is limited to the flower only — Lathyrus, Matthiola, 

 Althaea, Cheiranthus; in other cases, the intense pigmentation of the 



