146 Scientific Proceedings, Royal Dublin Society. 



pressures and with electrical conductivity measurements (10 A), these 

 observations were laid aside till February, 1912, when the study was resumed. 

 The distribution of oxydase in microscopic sections of the tissues of a large 

 numberof plants was studiedby means of the guaiacum reaction. Onbecoming 

 acquainted with the researches of Keeble and Armstrong (15, 16, 17), other 

 reagents, such as a-naphthol, benzidine, and j9-phenylen diamin, were also 

 employed. Alcoholic solutions of these penetrate tissues more readily than 

 does guaiacum, and so have obvious advantages. It would be tedious to 

 enumerate the tissues which afforded the direct or indirect reaction, but a few 

 cases seem worthy of mention. 



The very general presence of abundant oxydase in the pliellogeu layer of 

 stems is remarkable, and suggests that the enzyme may have an important 

 function in the formation of cork. In this connexion it may be remarked 

 that while cork cells afford no oxydase reaction, they readily adsorb guaiacum 

 on their walls. Tlius a section which has been treated with this reagent, when 

 further treated with potassium ferricyanide to detect tannin, immediately 

 develops an intense blue in the cork, while the general blue colour of the cells 

 containing oxydase is only slightly intensified. 



This behaviour of cork is in marked contrast to tliat of sclerenchymatous 

 tissue, the walls of which are very generally reactive with oxydase reagents, 

 even when none of the tissue of tlie cortex or bundle is so, as in the Iris 

 gertnanica leaf. In Catalpa bignonioides the cells of the cortex sheathing the 

 sclerenchymatous strands of the stem gave a marked oxydase reaction with 

 o-naphthol. Thus the evidence of the distribution of oxydase lends support 

 to the view that the enzyme is concerned in the production of the hardened 

 cell-walls.' 



In carrying out some of these reactions on stems of Rosa rugosa, it was 

 seen that while many cells contain tannin, as shown by tlie potassium ferro- 

 cyauide and ammonia reaction, the cells of the epidermis, colourless otherwise, 

 afford a bright green colour with these reagents. The epidermal hairs also 

 appear green ; but I do not at present know to what this colour is due. 



Petals of Rosa rugosa, white, were found to contain tannin, as did also 

 the stamens. These did not darken perceptibly at the torn edges, nor did 

 they give an oxydase reaction with guaiacum or a-naphthol. On the other 

 hand, red petals of the same plant bleached when placed in an alcoholic 

 solution of a-naphthol. A pink colour is produced on adding hydrogen 

 peroxide ; but this soon fades. The addition of water at this stage restores 

 the bright-red colour, tlie veins becoming especially prominent. The purple 

 colour given by the oxidation of a-naphthol appears only at the cut edges of 



' I find that Keeble and Armstrong (15) make a similar suggestion. 



