286 Oxydases and Pigments of Plants 



epidermal cells nor those of the epidermal hairs contain pigment, these 

 elements give pronounced oxydase-reactions and they constitute the 

 tissue to which pigment is confined in those pale reddish-stemmed 

 varieties which have a minimum of pigment. Next to the epidermis, 

 the sub-epidermal layer is, of all tissues outside the stele, richest in 

 oxydase, and it is in the sub-epidermal layer that pigment occurs in 

 the varieties somewhat more pigmented than those which belong to 

 the category of pale reddish-stemmed forms. In the case of green- 

 stemmed and reddish-stemmed varieties, the distribution of oxydase 

 in a member of the series is indicative of the distribution of pigment 

 in the next higher member of that series. 



It is only in dark red-stemmed varieties, e.g. Mt. Blanc Star, that 

 the pigment extends to any considerable depth into the cortex. These 

 varieties are remarkable also for the fact that their anthocyan pig- 

 ments are not limited to the epidermal and cortical tissues systems, but 

 occur also in those of the stele (vascular cylinder). As is the case with 

 all pigmented tissues of the epidermis and cortex, the pigmented tissues 

 of the stele give clear evidence of a high oxydase content. 



Therefore we have a further means of testing the hypothesis; for 

 by analogy with the distribution of oxydase in the progressively less 

 pigmented members of the colour series we may expect to find that the 

 localisation of oxydase in those forms which are without pigment in 

 their stelar tissues coincides with that of the pigment in the corre- 

 sponding tissues of the dark red forms. 



Appropriate examination shows that this anticipation is realised. 

 For example, the pigment in the stelar tissues of the flower-peduncle 

 of a dark red-stemmed plant occurs in the pericycle and in patches of 

 pith cells which lie against the protoxylems of the wood ; and these, 

 together with the phloem, are the tissues which are rich in oxydase. 

 In the root of a dark red-stemmed plant, large quantities of pigment 

 occur in the pericycle, in the medullary rays which extend from near 

 the periphery of the stele almost to the centre, and also in the phloem. 

 The distribution of oxydase in the stele of the green and reddish 

 varieties is very similar to that of the pigment of the red varieties. 

 Thus the flower-peduncle of a green-stemmed plant contains oxydase in 

 considerable quantity in the pericycle, phloem, and in the pith cells 

 which abut on the protoxylems. 



We conclude therefore that those tissues which in non-pigmented 

 forms are richest in oxydase are the tissues in which in coloured forms 

 pigment makes its appearance. 



