220 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



which have been shown to consist of a peroxidase plus a 

 peroxide, use will be made of the following terminology 

 viz., " complete peroxidase system " as equivalent to the 

 enzyme plus peroxide, and " incomplete peroxidase 

 system " or simply " peroxidase " to denote the enzyme. 



The addition of hydrogen peroxide has been mentioned 

 above. That this substance is not identical with the 

 naturally occurring peroxide is proved by the almost 

 universal presence of catalase in plant tissues. This 

 enzyme, for the existence of which as an individual there 

 seems now to be quite sufficient evidence, splits up hydrogen 

 peroxide in such a way that the oxygen is liberated in the 

 molecular condition, as is shown by its inability to effect 

 oxidation. When the peroxide is decomposed by platinum 

 black, oxidations may result if suitable compounds are to 

 hand. 



COMPOSITION AND PROPERTIES OF LACCASES OR 

 PHENOLASES. 



For a full account of the methods of preparation of 

 accase, tyrosinase, and artificial oxidases, the reader is 

 referred to the monographs by Kastle (1910) and by Clark 

 ( 1910), and to Euler's " General Chemistry of the Enzymes." 

 The effects of small quantities of acids, alkalies, and man- 

 ganese salts upon the activity of these enzymes is also 

 considered there as well as the identity of Medicago-oxidase 

 with a mixture of calcium salts of organic hydroxy acids, 

 including glycollic, citric, malic, and mesoxalic. A short 

 account will, however, be given of other features of 

 interest in connection with these enzymes. 



As previously mentioned, laccase acts upon many 

 phenols. It derives its name from its presence in the 

 latex of the lac-tree, Rhus vermicifera, the white juice of 

 which it converts into a smooth dark varnish or lacquer, 



