284 Oxydases and Pigments of Plants 



much more widely distributed than in the green and reddisli stemmed 

 forms. For example the flower-peduncle of the dark red-stemmed 

 variety Mt. Blanc Star contains pigment not only in the epidermis and 

 in three or more outer layers of the cortex but also in the tissues of the 

 stele (vascular cylinder). 



If the investigator has these facts of variety of pigment distribution 

 in mind he will not be surprised to discover when he proceeds to 

 determine the distribution of oxydase that, although oxydase is present 

 in every pigmented cell, it is not necessarily confined to these cells. 

 This fact might appear at first sight to militate against the hypothesis 

 which associates pigment formation with oxydase action ; but further 

 consideration shows that it does not. For it is evident that oxydase 

 and chromogen, though they interact to form pigment, may be produced 

 independently one of the other and therefore the failme of certain 

 tissues, rich in oxydase, to produce pigment may well be due to the 

 absence of chromogen. Or, to express the idea in other terms, chromogen 

 and not oxydase is the factor the lack of which limits pigmentation in 

 P. sinensis. The evidence offered b}' the known facts of the Genetics of 

 this species lends weighty support to this conclusion and indeed leads 

 directly to the expectation that one of the two agents concerned in the 

 production of anthocyan pigment is more generally distributed than the 

 other. 



For if the two agents, chromogen and oxydase, were equally sus- 

 ceptible of restriction of distribution in the plant then it would be 

 reasonable to expect that two types of green-stemmed plant exist; one, 

 green-stemmed because it lacks chromogen, the other, because it lacks 

 oxydase. In point of fact, and in spite of the large amount of breeding 

 work which has been carried out with this species, only one type of 

 green-stemmed plant is known in P. sinensis. 



The evidence from Genetics in support of this statement is clear. 

 Some plants, for example Stocks and Sweet Peas, show by their genetical 

 behaviour that either of two factors for pigment production may be 

 lacking from a variety. 



In such plants, as Bateson, Miss Saunders and Punnett (1906) 

 have proved, it is possible, by mating white-flowered individuals of the 

 two types, to bring the complementary colour factors together and thus 

 to produce a reversionary, coloured F^ generation. But with P. sinensis 

 a like result has never been obtained. A pure green-stemmed variety 

 mated with any other similar variety gives rise to a green-stemmed Fi 

 generation, and pure breeding white-flowered varieties, each of which 



