158 Scientific Proceedings, Royal Dublin Society . 



of great value.^ It appears that the results obtained may be interpreted 

 in two different ways: (1) that the coloration of the reagents is due 

 to specific oxydases, for certain tissues are found to react with one and 

 not with another ; (2) that one oxydase is present, but that in certain 

 tissues reducing agents are located, that is to say substances more readily 

 oxidized than the artificial or natural chromogen. Such reducing agents 

 would rank as apparent inhibitors of oxydase action ; but possibly substances 

 which totally inhibit oxydase action are present. From the fact that, 

 as shown by Keeble and Armstrong (5), for Primula sinensis and other 

 plants, hydrogen cyanide is able to remove an inhibitor, after which all 

 three reagents act intensely, it seems almost certain that the one oxydase 

 interpretation is correct ; and that the different natural and artificial 

 chromogens are susceptible to its action to different extents on account 

 of the interference of the inhibitor. These points will be more evident 

 when the reactions with various flowers are considered in detail. 



(ff) Oxydases in Isis gbrmanica Leaf. 



As is well known, the sword-shaped leaf of /. germanica is peculiar in 

 that it has been folded in two along its length, so that its morphological 

 upper surface constitutes the inner side of the fold. This upper surface is 

 devoid of stomata and is pressed against the under — namely, the outer — 

 surface of the next adjacent leaf. The bases of the leaves are whitish. 

 About half-way from the base the upper surface disappears altogether, 

 so that the two sides of the leaf-blade are entirely bounded by what is 

 morphologically the under-epidermis. The leaf is mainly composed of 

 compact parenchyma traversed by parallel vascular bundles. In the latter 

 the wood is toward the upper (inner) surface, and below it is the bast and 

 a very noticeable triangular mass of sclerenchyma. There is a somewliat 

 indefinite bundle-sheath round the whole. 



Transverse sections of the green lower portion of the leaf, growing under 

 normal conditions, when treated with guaiacum and peroxide frequently 

 develop a blue colour in the wood and always in the sclerenchyma, but 

 the bast, epidermis, and mesopliyll are usually unaffected. Even when some 

 colour is shown by the last two tissues, application of sap from the whole 

 leaf pounded up destroys it. Treatment of sections with hydrogen cyanide 

 serves to remove an inhibitor, so that when tested a blue colour appears 

 all over. The upper portion of the leaf contains no inhibitor, for it gives 



' The problem of deciding between a slight positive result and a negative one with the reagents 

 employed is always difficult, particularly in the epidermis and especiiiUy so with benzidine, as the 

 solution may have a faint brown tinge even when quite fresh. 



