304 Oxydases and Pigments of Plants 



G. TJie Nature of the Oxydases in FloxDers. 



(1) The Oxydases and Peroxydases of Prmuda sinensis. 



As indicated in the footnote at the beginning of the section the 

 term oxydase is used iu the foregoing sub-sections (A — F) to include 

 both oxydase and peroxydase, that is to say those oxidising substances 

 which react directly with benzidine or a-naphthol (direct oxydase) and 

 those which react with these reagents only after the addition of hydrogen 

 peroxide (peroxydases). Our reasons for the practice which we have 

 adopted are threefold: first to simplify description; second because a 

 given tissue may yield, in one variety, an oxydase reaction and, in 

 another variety, a peroxydase reaction ; and third because there is 

 evidence that a tissue of a given variety at one time and under one set 

 of circumstances may contain peroxydase, and at another time and 

 under other circumstances may contain a complete oxydase — namely 

 peroxydase plus organic peroxide — and so give a direct reaction. 



It is necessary therefore to describe the results of our observations 

 on the nature of the oxydase content of the various tissues of P. sinensis 

 and of the other plants which we have investigated. 



In the case of P. sinensis direct oxydases are relatively rare and 

 peroxydases are the rule. Thus the oxydase reactions of the petals of 

 coloured and recessive white flowers ai'e invariably or all but invariably 

 indirect ; in other words peroxydases are present in the flowers both in 

 the epidermis and in the tissues of the veins : hence we may speak of 

 epidermal peroxydase and bundle peroxydase as present iu the petals of 

 the flower. The only exception to this ride occurred in the case of the 

 flower of a Sirdar, one petal of which gave on one occasion a vvell marked 

 direct oxydase reaction. We have no evidence, except iu the single 

 example just recorded, of the existence of direct oxydase in the flower of 

 P. sinensis. We have satisfied ourselves, however, that it occurs in the 

 vegetative parts of normal plants. Thus sections of flower-peduncles of 

 dark red-stemmed varieties, of green-stemmed Sirdars and of reddish 

 varieties, may all possess direct oxydase in the phloem. In Sirdars and 

 in dark red-stemmed varieties there is evidence that the pericycle 

 contains a direct oxydase. On the other hand it is very rare indeed for 

 the epidermal tissues of plants grown under normal conditions to exhibit 

 a direct oxydase reaction. We have obtained such reactions occasionally 

 in certain red-stemmed varieties; for example sections of flower-peduncles 

 treated with benzidine may give the colouration characteristic of the 

 oxydase reaction in the epidermal cells as well as in the phloem. 



