F. Keeble and E. F. Armstrong 305 



For reasons which will be apparent immediately there is no need to 

 attempt to discriminate more closely between the distribution of per- 

 oxydase and that of oxydase in the normal flower. What is evident 

 and of importance is the fact pointed out already by Miss Wheldale and 

 by Clark that peroxydase is more widely distributed than the organic 

 peroxide which activates it. Even in the case of the phloem which, as 

 we have seen, gives a direct reaction there appears to be more per- 

 oxydase present than the organic peroxide is capable of activating ; for 

 the result of adding hydrogen peroxide to sections which have already 

 given a direct reaction, is to increase that reaction. Hence it would 

 appear that the efficiency of the system, peroxydase and organic per- 

 oxide, is determined by the extent to whicli the organic peroxide is 

 present, and that whereas peroxydase is relatively stable, the organic 

 peroxide is unstable. 



We have satisfied ourselves not only that this is the case but that 

 external conditions play an important part in determining the amount 

 of peroxydase present in the tissues of a plant. 



(2) The Oxydases and Peroxydases of Other Flowers. 



Before proceeding to justify this statement we will describe briefly 

 the nature of the oxydases in the various plants to which reference is 

 made in the preceding pages and in certain other species which we 

 have had occasion to examine. 



Flowers of the Sweet Pea and of the Culinary Pea contain no direct 

 oxydase in their epidermis and either none or a very small amount 

 in the veins. They give, however, well marked peroxydase reactions. 

 Geranium sanguineum possesses direct oxydase both in the epidermis and 

 bundles of the petals. The pale flesh-coloured variety G. lancastriense 

 contains direct oxydase in its veins and peroxydase in its epidermis. 

 The white variety contains in its epidermis neither oxydase nor per- 

 oxydase, but its bundles give a distinct peroxydase reaction. 



Coloured varieties of Sweet William give good oxydase i-eactions in 

 both bundles and epidermis. 



Species of Primus and Pyrus are of interest in this connection. 

 Those species the flowers of which are white, and remain white on 

 fading, contain peroxydase only; those species which turn brown on 

 fading contain direct oxydase. 



The very general phenomenon of browning presented by dried plants 

 is to be regarded in all probability as an indication of the presence of a 

 direct oxydase, and in order to prevent the discolouration of herbarium 



21—3 



