222 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



activity of sap which had stood. Consequently both con- 

 stituents of the oxidizing system must have been destroyed 

 by heat. Other experiments showed that the peroxide 

 is less stable than peroxidase towards heat. 



THE INFLUENCE OF LIGHT UPON THE AMOUNT OF OXIDASE 

 IN PLANT TISSUES CONSIDERED IN RELATION TO THE 

 COMPOSITION OF THE ENZYME. 



The effect of light upon the oxidase content of plants has 

 been studied by Keeble and Armstrong (1912, 3). By 

 means of the laccase reagents, a-naphthol and benzidine, 

 they satisfied themselves that the tissue of a normally 

 illuminated plant contains less peroxidase than does the 

 corresponding tissue of a plant kept in darkness ; also that 

 the organic peroxide constituent of the complete oxidase, 

 though it may be absent from the normal plant, frequently 

 makes its appearance after that plant has been maintained 

 for some time in darkness. Thus it is clear that the 

 diurnal alternations of light and darkness must in this 

 respect alone have a very marked influence upon the 

 metabolism of plants. 



While engaged in testing the influence of light upon the 

 distribution of peroxidase in the flowers of Iris spp., in the 

 course of an investigation upon the correlation of enzyme 

 and anthocyan pigment, the author (1915, 1) found that 

 Iris flowers never contain organic peroxide normally, and, 

 owing most probably to the presence of an inhibitor, 

 many varieties show but little peroxidase. Some species 

 show a marked increase of oxidizing power when placed 

 in the dark for twenty-four hours, and indeed, prolonged 

 darkness leads to the appearance of peroxidase in flowers 

 from which it had been absent. In a few cases, however, 

 deeply pigmented Irises gave no peroxidase action either 

 before or after enclosure in a dark chamber, even when the 



