THE PLANT OXIDASES 233 



remarkable, that of the sunflower (Helianthus multiflorus) 

 becoming a very intense dark brown within a few minutes. 

 Among other saps which, in the author's (1913) experience, 

 darken rapidly may be mentioned those from the leaves 

 of Hedera helix, Syringa vulgar is, Magnolia acuminata, 

 Catalpa bignonioides, Fraxinus oxyphylla, and F. excelsior. 

 A great many plants, however, give a light-coloured sap 

 which does not darken on standing. In this group are 

 included Wistaria sinensis, Eucalyptus globulus, Chamcerops 

 humilis, Cordyline australis, Equisetum telmateia. These also 

 fail to colour the artificial chromogens till after the addition 

 of hydrogen peroxide, or of an old sample of an essential oil, 

 such as turpentine, in which peroxide formation has taken 

 place. In this class the organic peroxide constituent of the 

 ,peroxidase system may be supposed to be lacking. 



PLANTS CONTAINING INHIBITORS. 



Yet again in a third group of plants no peroxidase can 

 be detected in the sap even after the addition of peroxide. 

 This includes the leaf saps of Iris germanica, Aspidium 

 filix-mas, and Pteris aquilina. Only the mature leaves 

 of the last-named behave in this manner, for the young ones 

 give the indirect action. In all these cases, however, it 

 has been found possible to demonstrate the presence of 

 peroxidases by dialysis of the sap, from which an inhibitor 

 diffuses out, or by precipitation of the enzyme with alcohol, 

 as described in a previous section. [See note, p. 250.] 



OCCURRENCE OF PHENOLASES AND TYROSINASES. 



The presence of oxidases of the phenolase (laccase) type 

 has been demonstrated in every land plant thoroughly 

 examined; certain tissues may fail to give the usual tests, 

 owing to inhibitors having been produced, or possibly a 



