472 M. Wheldale. 



of anthocyanin in the vegetative parts is either red or magenta. 

 Artificial conditions, such as low temperature, feeding- with carbo- 

 hj^drates, etc. would not alter the kind but only the amount of pig- 

 ment developed. In the same way no metabolic change will induce 

 colour-formation in an albino. Katie found this to be true of onion 

 bulbs; variations in temperature, light or nutrition failed to bring 

 about development of anthocyanin in the bulbs of an albino variety, 

 whereas similar changes produced an increase of pigment in the bulb 

 scales of the anthocyanic type. 



In addition to the red and magenta classes in Antirrhinum there 

 are pale and deep varieties in each class; for the magenta, it has 

 been shown experimentally that the pale variety is dominant to the 

 deep and contains a definite factor which causes partial diminution 

 of the colour. Here, again, if, by artificial means, we increase the 

 formation of pigment in the vegetative parts, the anthocyanins 

 produced in the pale and deep varieties will be respectively of the 

 pale and deep kinds. 



The distinction which I have drawn between total and partial 

 inhibitors may it is true, be one of degree only. Partial inhibition 

 may quite well be due to the presence of a reducing sugar, the pro- 

 duct of some hydrolysing enzyme and not necessarily to a specific 

 reductase antagonistic in action to the oxydases. Such speculations 

 must however be left for the present until more biochemical evidence 

 is provided. 



Attention may nevertheless be drawn to the distinction between 

 tinged or picotée varieties and inhibited varieties. The tinged varieties 

 as far as we know for genera examined are lacking in one of the 

 oxygenases essential for full colour, so that insufficient oxydation is 

 the cause of lack of colouring. Inhibited varieties, on the other hand, 

 have all the mechanism for full colour production but in addition 

 they carry a factor which limits the extent of oxidation and hence 

 the intensitv of colouration. 



