96 MASS. EXPERIMENT STATION BULLETIN 175. 



partial starvation, as it were, not, however, serious enough to reduce 

 greatly the total starch formation and assunilation of the whole plant; 

 while at the same time the chlorophyll production is very little changed 

 if a comparison of the color of the normal and treated leaves can be taken 

 a,s a basis of such a comparison. This latter fact has already been noted 

 by Lodewijks in his work on the disease. 



It is, therefore, indicated by the results obtained in the preceding ex- 

 periments that the different colors have Httle or no effect on the causal 

 agent of the disease, but in the case of the blue there is a strong depres- 

 sion of the macroscopic sjmiptoms of the disease. 



Biochemical Studies. 

 Enzyme Activities in Healthy and Diseased Plants. 



The study of enzymes in relation to diseases, particular!}' those of a 

 so-called physiological nature has not been extensively gone into as yet 

 by investigators, but it is believed that a study of their activities and 

 reactions should be made, not only in the case of physiological troubles, 

 but also those caused by fungi and bacteria, as it is the writer's firm behef 

 that the activities of a large number of the fungi, and their effects on the 

 respective hosts, are in a great measure due to the action of either exo- 

 enzymes or endoenzymes produced by the fungi concerned. There is a 

 possibility that the future may show a great advance in the study of 

 host resistance, etc., when the conditions under which enzyme activity 

 in fungi and bacteria takes place are better known, and plants may pos- 

 sibly be bred to a condition of producmg either a sap in wliich these 

 activities cannot take place, or will produce anti-enzymes which will 

 inhibit the activities of the enzymes contained in the respective fungi. 



Although many have made a study of this disease, very few have con- 

 cerned themselves mth the question of the enzj-nne activities; among 

 the first to make mention of this phase of the question was Woods {loc. cit.), 

 who found that the enzymes designated as peroxidases were at least dif- 

 fusable, and occurred apparently in larger amount in diseased leaves than 

 in healthy ones; also that their action was t\\dce as strong in the light 

 green areas as in the darker portions of the leaf. Koning {loc. cit.), as a 

 result of his investigations, came to the conclusion that the disease was 

 caused by a certain enzyme, which he stated to be oxidase, and the action 

 of which he described. He beUeved that it was formed in the plant under 

 certain conditions. HeintzeP also found oxidizing enzymes present which 

 were more active, if not present in greater amounts, in diseased plants 

 than in the normal plants. Woods later (1902), in his work on the mosaic 

 disease, verified Ixis former observation, and stated further that the 

 diastase activity was much inhibited in the case of diseased plants. He 

 attributed the lessened diastase activitj^ to the presence of excessive 



« Heintzel, K.: Contagiose Pflanzenkrankheiten ohne Microben mit besonderer Beriicksichti- 

 gung der Mosaikkrankheit der Tabaksblatter. Erlangen, 46 p., 1 pi. (Inaugural Dissertation) 

 (1900). 



