274 RESPIRATION, FERMENTATION AND DIGESTION 



toplasm and* the process constitutes one form of respiration. 

 Certain of these enzymes might also operate to break up hydro- 

 gen peroxide when formed in the plant and thus prevent its 

 poisonous action on the protoplasm. 1 Two groups may be dis- 

 tinguished, viz., the oxidases proper, which are destroyed in 

 aqueous solutions by temperatures of 65 ° to 70 ° C, and the 

 peroxidases which disintegrate at 8o° to 85° C. Both act most 

 readily in slightly acid solutions : Catalase, however, does not 

 fall in either of the above groups from which it varies in many 

 properties. 



Oxidizing enzymes are widely distributed in plants, and do not 

 decompose readily upon the death of the cells, but produce many 

 post-mortem changes in the constituents of the plant, and may 

 even pass out into the soil upon the complete decay of the plant 

 remaining unimpaired for long periods. Various bleaching and 

 curing processes, development of flavors, preparation of indigo, 

 fermentation of tobacco, and silage, and other commercial opera- 

 tions are dependent upon the action of these substances. The 

 well-known coloration, or browning of the exposed surfaces of 

 apples and other fruits is an example of the action of oxidases. 



The development of an excessive amount of oxidase in plants 

 subject to defective nutrition, and many kinds of cultural treat- 



1 Loew, O. Curing and fermentation of cigar leaf tobacco. U. S. Dept. of Agri- 

 culture. Report No. 59. 1899. 



Loew,- O. Physiological studies of Connecticut leaf tobacco. U. S. Dept. of 

 Agriculture. Report No. 65. 1900. 



Woods, A. F. Brunissure of the vine and other plants. Science, N. S. 9 : 508. 

 1899. 



Woods, A. F. The destruction of chlorophyll by oxidizing enzymes. Centralbl. 

 f. Bakteriol. Parasitenk. u. Infektionskrankh. 5 : 745. 1899. 



Woods, A. F. Inhibiting action of oxidase upon diastase. Science, N. S. 11 : 

 17. 1900. 



Loew, O. Catalase : a new enzyme of general occurence. U. S. Dept. of Agri- 

 culture. Report No. 68. 1901. 



Woods, A. F. Mosaic disease of tobacco. Abstract, Science, N. S. 13 : 247. 

 1 901. 



Green, J. R. The soluble ferments and fermentation. Chapter 19. 1899. 



Aso, K. A physiological function of oxydase in kaki-fruit. Tokyo Bot. Maga- 

 zine, 14 : 179. 1900. 



