294 Oxydases and Pigments of Plants 



epidermal and bundle oxydases; the most deeply coloured flowers 

 contain most, those of intermediate tint, less, and those which approach 

 most nearly to whiteness, contain the least amount of oxydase. The 

 coincidence of oxydase with pigment in the all but white forms of flower 

 is most impressive. In such forms the pigment is confined to three 

 short rosy lines at the base of the limb of each petal and it is only 

 along these lines, which mark the position of the main veins, that 

 oxydase is found. These approximately white forms give but a light 

 brown reaction with benzidine ; the pink pigmented forms give a rich 

 brown and the fully pigmented forms give a brown-black reaction. 

 Hence we conclude that in this example of an ever-sporting flower the 

 extent and depth of pigmentation are determined by the quantitative 

 distribution of oxydase. 



(2) White Varieties of Sweet William. 



Among the various, non-sporting varieties of Sweet Williams which 

 we have examined are races with fully coloured, white and nearly white 

 flowers. The fully coloured varieties all give pronounced oxydase 

 reactions ; the white and approximately white varieties behave to our 

 reagents in one of two ways. The pure white race gives a very definite, 

 albeit limited, oxydase reaction which is most pronounced in the central 

 region towards the base of the petal limb. This variety is therefore 

 colourless because it lacks chromogen. The all but white race, the 

 petals of which bear a ring of rosy dots or lines about one-third of the 

 way from the point of junction of limb and claw, contains no oxydase 

 except in the region which in the fresh flower is occupied by the rosy 

 ring. Hence this variety, unless indeed it prove to be a dominant 

 white, owes its whiteness to lack of oxydase. 



The final establishment of these conclusions must await the results 

 of breeding-experiments which are being carried out. 



Should these experiments lead to the production of a coloured F^ 

 generation, we shall have the proof of the hypothesis suggested first 

 by Miss Wheldale, that, where two colour factors are involved in the 

 production of pigment, one is a chromogen producing factor and the 

 other an oxydase producing factor. But apart from these experiments 

 we have in the cases of white, magenta flaked P. sinensis and of the 

 various races of Sweet William clear evidence that pigment formation 

 depends on oxydase action, that depth of colour is determined by amount 

 of oxydase and that a lack of this substance results in an absence of 

 pigmentation. 



