,,S SCIENCE PROGRESS 



With regard to the chromogens it is found that the quantity 

 of the autoxidised materials normally present is insufficient to 

 impart a colour to the cells which are continuously manu- 

 facturing reducing substances. But upon the death of the 

 cells or upon the shortage of supplies of materials necessary 

 for metabolism, the activity of the oxidase is unchecked and 

 many changes are effected, among them being the production 

 of sap-soluble pigments from the chromogens. The latter may 

 be tested for by pressing some sap from the organ under 

 examination. If this appears brown it is invariably found 

 that an oxidase is present, together with organic peroxide 

 and chromogen. If no colour is produced it must be further 

 tested by the addition of hydrogen peroxide. The darkening 

 of the sap then takes place if it contains a chromogen, unless 

 oxidase action is hindered by an inhibitor. In this eventuality 

 a considerable amount of an oxidase preparation has also to 

 be mixed with the sap in order to ascertain whether it will 

 darken or not. 



Distribution of Oxidases in Plants. — In the above paragraph 

 it has been assumed that oxidase is present, to some degree 

 at least, in every vegetable cell, and this I believe to be the 

 case in the large majority of land plants. Bourquelot and 

 Bertrand, 1 Zellner, 2 Pringsheim, 3 Kastle, 4 and others, have 

 shown that phenolases and tyrosinases are of almost universal 

 occurrence in fungi. Clark 5 tested a large number of groups 

 of flowering plants and pteridophytes, and has found pheno- 

 lases to be of very general occurrence : in certain strongly 

 acid saps, however, he failed to detect any oxidase ; Moore and 

 Whitley 6 also noted their absence from the pulp of lemons, 

 limes, and oranges. 



Some cases are met with in which the usual tests such 

 as guaiacum resin, benzidine, and a-naphthol fail to give any 

 reaction even after the addition of hydrogen peroxide. In 

 such tissues an inhibitor is usually present. For example, 



1 Bourquelot and Bertrand, Compt. Rend. Soc. Biol. 1895, 47, 582, and Bull. 

 Soc. My co I. de France, 1896, 12, 18. 



2 Zellner, Die Chcmie der Hohcren Pilze, 209, Leipzig, 1907. 



3 Pringsheim, Zcitschr. physiol. Chem. 1909, 62, 386. 



4 Kastle, J. H., Bull. No. 26, Hyg. Lab. U.S. Pub. Health & Mar.-Hosp. Sew. 

 Wash., 1906. 



5 Clark, E. D., loc. cit. 



' Moore and Whitley, Biochcm. Journ. 1909, 4, 136. 



