148 Scientific Proceedings, Royal Dublin Society. 



and hydrogen peroxide, the presence of Keeble's "bundle peroxidase" is 

 revealed in all the veins. But the surfaces of the leaves appear curiously 

 mottled with purple. This colour is seen to be confined to the tliree, four, 

 or five epidermal cells immediately abutting on the guard -cells of the stomata, 

 the guard-cells themselves being unaffected. 



Again, when leaves of Tradescaiitia virginica and Wistaria sinensis are 

 placed in alcoholic benzidine, it is seen that the guard-cells and the four cells 

 abutting on tliem become brown to a more marked degree than do the other 

 epidermal cells. Thus they seem to be considerably richer in oxydase. If now 

 a dilute solution of methylene blue be added to the leaf, after rinsing off the 

 benzidine, the epidermal cells become blue,' with the exception of the 

 guard-cells and the four adjacent cells, which remain brown, the nuclei 

 being especially darkened. 



This peculiar distribution of the enzyme may be related to the 

 mechanism of the movement of the stomata. The question is being worked 

 out further. 



The distribution of oxydase and reducing agent in Iris gernianica. 



The localization of oxydase in Iris gennanica is particularly interesting. 

 As far back as 1820 Planche (21) had noticed that the fresh roots (? rhizome) 

 of this plant gave the direct action with guaiacum. Sections across the 

 root of Iris give the indirect action with guaiacum and hydrogen peroxide. 

 Though tlie whole cortex gives the colour, it is most intense in the outermost 

 and innermost layers, the walls of the endodermis being deeply stained.^ Tlie 

 walls of the smaller vessels of the wood and of the central lignified tissue also 

 give the reaction, though none is given by the bast or the large vessels of the 

 wood. The whole root, when pounded up, turns guaiacum blue, so there can 

 be no inhibitor present in the tissues which do not give the reaction, or more 

 probably such a body is only present in small quantitj'. Sections through 

 the rhizome show the indirect oxydase reaction throughout, especially m the 

 thick-walled woody vessels of the bundles. Addition of potassium ferri- 

 cyanide to this section brings about the appearance of a deep blue in the 

 corky tissue, as already noted. 



In the leaf-sections the only oxydase reaction is, as before, the indirect 

 one with guaiacum, and that is limited to the wood walls and sclerenchyma 

 of the bundles.^ Further up the leaf it is entirely absent. Sap from the 



' I am indebted to Miss K. Hadden for this observation. 



' Cf. the previous suggestion as to the function of oxydase in cell-walls. 



^ Under certain conditions the oxydase reaction may be widespread. 



