386 ENZYMES 



of acid or alkali, which increases hydrogen or hydroxy! ion 

 concentration, will activate a hydrolytic enzyme. 



The reason why a plant extract containing oxidases will 

 no longer give the guaiacum reaction when heated to 60° is 

 that the peroxide, originally present in the juice, is destroyed, 

 but not the peroxidase. So that although the heated juice is 

 inactive, its oxidizing activity can be restored by the addition 

 of a peroxide. 



The work of Moore and Whitley is corroborated by 

 Wheldale,* who finds that the power of the direct action, but 

 not the indirect, is accompanied by the formation of a brownish 

 pigment when the part is injured or subjected to the action of 

 chloroform vapour. This action is common in the Composita;, 

 Umbelliferie, Labiatae, Boraginacea;, and certain genera of the 

 Scrophulariaceai, Rosacea;, Leguminosse, and Ranunculacea^. 

 In the Cruciferae, Caryophyllacese, Crassulaceae and Ericaceae 

 the action is either absent or very rare. In such cases she 

 finds the direct action to be due to pyrocatechin which, on 

 exposure to air, rapidly oxidizes and then acts as an organic 

 peroxide, thus enabling the peroxidase, which is almost uni- 

 versally present, to transfer oxygen to the oxidizable substance. 



In addition to oxidative processes carried out in the plant 

 by these enzymes, they may play an important part in the 

 preparation of raw food-material in the soil. Thus Schreiner 

 and Reid f as the result of their experimental work have come 

 to the conclusion that enzymes, principally peroxidases, are 

 excreted by the roots, and so oxidize organic substances in 

 the soil. Oxidation was found to be most potent in the root- 

 hair regions and those places where the secondary roots are 

 developing. The older parts of the root and also the root-cap 

 do not produce these enzymes. The degree of the activity of 

 the enzymes in the soil depends upon the character of the soil ; 

 thus the presence of sodium nitrate accelerates the oxidative 

 processes, and, in brief, the most productive soils show the 

 most vigorous oxidation. On the other hand, the reverse 

 obtains in poor unproductive soils which contain substances 

 which interfere with the process. These deleterious agents 



* Wheldale: " Proc. Roy. Soc, Lond.," B., 1911, 84, 121. 

 t Schreiner and Keid : " Bot. Gaz.," igog, 47, 355. See also Schreiner and 

 Sullivan : id., 1911, 51, 156, 273. 



