Atkins — Oxjjdases and their Inhibitors in Plant Tissues. 167 



reaction, for in the white variety the a-naphthol reaction is well marked in 

 them. In /. ovientalis, on the otlier hand, the epidermis gives a slight 

 a-naphthol reaction ; but in the veins it is well defined. 



In I. ochroleuca, I. tenuifolia {?) , and the deep and pale j'ellow varieties 

 Nos. 30 and 31, anthocyan chromogens are absent, except where brown 

 markings are on the hafts in the two latter cases, for the pronounced oxydase 

 reactions of both veins and epidermis lead to this conclusion, there being no 

 inhibitors present. In /. Kaempferi the reactions are on the whole well marked, 

 though there is evidently an inhibition patch, white, extending beyond the 

 yellow plastid area. In the two varieties of /. pseiichicoi-Kv the distribution 

 is quite different, for there is no trace of reaction with a-naphthol and hardly 

 any with benzidine in tiie veins. Treatment with hydrogen cyanide, how- 

 ever, removes an inhibitor, so tliat just as intense a reaction is given as with 

 tlie two other yellow varieties JSTos. 30 and 31. Probably the yellows with 

 inhibitor would behave as dominants if crossed with purple varieties, whereas 

 those without inhibitor would very likely be recessives, the resulting hybrid 

 having both yellow and purple superposed or mingled. The carrying out 

 of breeding experiments with Iris varieties, on lines similar to the work of 

 Xeeble, Armstrong, and Jones on Primulas, would be of great interest. 



The effect of the age of the flower upon its oxydase reactions was not 

 investigated, for no more material was available owing to the lateness of the 

 season. It is remarkable that the direct action was only observed in one case 

 in traces ; in all the others tlie addition of peroxide of hydrogen was necessary. 

 All the flowers, however, were gathered in bright summer weatlier, so it is 

 possible that the natural peroxides wouhl liave been found in unopened buds 

 or at night, for Keeble and Armstrong have shown that the supply of these 

 substances is augmented by keeping Primula flowers in tlie dark for a day. 

 These questions, and others, such as deciding in which cases, if any, the 

 yellow plastid pigment was replaced by a yellow sap pigment, await further 

 investigation next summer. 



Examination of a number of herbarium specimens of Iris shows that the 

 flowers of some turn a dark brown in drying, while others remain of a light 

 colour. Owing to tlie influence of the gums used, it is not possible to be 

 dogmatic ; but it seems almost certain that those which become brown, such 

 as /. ijermanica, I. florentma, I. sambiiciua, I. ^;yre«rt«c«, /. acutiloba, &c., are 

 the ones with plentiful oxydase supi)ly ; whereas others which preserve their 

 natural light shadeSj such a.s I.p>>eHdavorHS,I. aeqniloba, I. squakiis, I.chinensis, 

 (epidermis), &c., contain inhibitors. It has been sliown in this paper that 

 /. pseudacorus does contain an iuliibitor. 



