546 EXPERIMENT STATION RECORD. 



questions relating to the physiologj^ of the leaf and the ehemico-phj^si- 

 ologicUl changes which take place in processes of curing and sweating. 



The acidity in the plant was greater in the morning than in the 

 evening. "The custom of harvesting tobacco on bright sunny days 

 has, therefore, a sound physiological foundation." The upper leaves 

 contain more acid than the lower leaves. The acidity of the lamina 

 decreased as the process of curing in the plant proceeded. 



The presence of diastase in tobacco leaves was determined by the 

 author, as was also a proteolytic enzym. The latter differs from the 

 ordinar}' trypsin in that it can not attack fibrin and casein under 

 ordinary conditions, while it can attack dissolved albumen. The pres- 

 ence of a cellulose-dissolving enzym (c3^tase) in tobacco leaves was not 

 determined with certainty. In tests with oxidase and peroxidase both 

 seemed to have the main character of albumoses. Oxidase in the juice 

 of the tobacco leaf diluted with about 20 parts of water was killed by 

 heating to Q6 to 67° C. for 3 minutes. The presence of certain alkalies 

 increases the resistance of oxidase to heat, Avhile acids decrease it. 

 Peroxidase in an alcoholic mixture was killed at the temperature of 

 70° C, while in a mixture of ammoniiun sulphate the enzym was not 

 killed after heating for a short time to 93° C. 



Since manganese has been found as a regular ash constituent of the 

 oxidases, it was thought desirable to see what woidd be the iniluence 

 of fertilizing tobacco with solutions containing manganese. A 0.1 per 

 mille solution of sulphate of manganese was used to water some tobacco 

 plants until each had received 0.6 gm. of that salt. Examination of 

 the ripe leaf showed no noticeable increase of oxidase or peroxidase 

 in the plants so treated. 



A third oxidizing enzym in the tobacco plant, to wijich the name 

 catalase is given, was observed. It occurred in the uufiltered juice of 

 fresh tobacco leaves. 



"This enzym is killed at 72 to 75° C. (161 to 167° F.). It is an oxiilizing enzym, 

 [but] it differs essentially from the ordinary oxidase and peroxidase. 



"This enzym is the most durable of those in the tobacco leaf mider ordinary cir- 

 cumstances, since it occurs in tobacco even over 6 years old, in which no trace of 

 other enzyms, not even of the peroxidase, can be found. 



"It is certainly an important factor in the heating up of the tobacco pile, as recent 

 experiments with fermenting tobacco have shown. 



"The general occurrence of this enzym in plant as well as in animal cells suffices 

 to indicate a highl}' important physiological role. It is probably intimately con- 

 nected with the proce.ss of respiration. The following two hypotheses as to its func- 

 tion appear the most probable to the writer: (1) Since many oxidative processes lead 

 to the formation of hydrogen peroxid as a by-product, it is important that such a 

 poisonous by-product be at once destroyed when accidentally formed in the cells in 

 the course of the respiratory oxidations. (2) This enzym may have the office of 

 loosening affinities in fatty acids and sugar in order not to tax the chemical energy 

 of the protoplasm itself too heavily when these compounds are consumed for the 

 purpose of respiration." 



