282 Oxydases and Pigments of Plants 



and second, on the extent to which they are preserved from the access 

 of light. Many of our preparations with benzidine retain their 

 colour for months, but the colours produced by the use of a-naphthol 

 may show signs of fading within a sliorter perind. Sections may be 

 mounted either in glycerine jelly or may be taken up rapidly through 

 the alcohols and mounted in Canada balsam. 



In the case of large objects such as fruits the reagent may be painted 

 on to the surface to be studied and the reaction examined by reflected 

 light. 



It is noteworthy that, as we show in the text and illustrate in 

 Figs. 4 and 5, Plate XIX, the only reagent which gives a satisfactory 

 reaction with the epidermal oxydase is benzidine, and that benzidine 

 and a-naphthol discriminate as it were between epidermal and bundle 

 oxydases. The former is picked out by benzidine but is untouched or 

 almost untouched by a-naphthol. Tiie latter gives strong reactions 

 with a-naphthol and benzidine. The behaviour of a-naphthylamine is 

 very similar to that of a-naphthol. 



The colour of the reaction with benzidine is a rich brown due to the 

 deposition of the oxidised product in the cells. Under certain circum- 

 stances, and in early stages, this reagent produces a blue or blue-green 

 colour which however passes more or less rapidly into brown. The 

 i-eactiou with a-naphthol takes the form of a delicate lilac blue or 

 lavender colour, and that with a-naphthylamine, a pink. 



It remains to mention that the i-eagents should be made up 

 fresh for use and that the flowers or other subjects to be investigated 

 should be fresh, uninjured, and in good growing condition. Late formed 

 flowers, for example, are apt to give uncertain results and this is in 

 conformity with the fact that such flovvers show often considerable 

 departure from their normal colouration. The length of time of 

 exposure to the several reagents varies with the object and can be 

 decided only by trial. In the case of sections, the reaction takes place 

 almost immediately ; but solid objects such as whole corollas require to 

 be incubated for 1, 2 or more hours. 



