144 



EXPERIMENT STATION. 



[Jan. 



or /? catalase extracted from normal and diseased plants. The 

 results in this case indicated also that the leaves affected with 

 mosaic disease were deficient in soluble catalase. The results 

 obtained are tabulated below : — 



Table showing Oxygen develojied by ^ Catalase in Eeallhy and Diseased 



Plants. 



Average. 



Healthy leaves, 

 Diseased leaves, 



C.C. 



35.80 



21.80 



The foregoing results show plainly that catalase is greatly 

 deficient in both a and j8 form in leaves affected with the mosaic 

 disease. 



As catalase is possessed of the property of decomposing 

 hydrogen peroxide, and as it is a well-established fact that 

 hydrogen peroxide is highly injurious to plant life, and also 

 that it may possibly be formed ^ as an intermediary step in the 

 various metabolic changes in plant growth, it is an interesting 

 problem to discover whether the lack of catalase is a prime 

 factor in the production of the mosaic disease. Work along 

 these lines will be continued, and the results announced in a 

 future report. 



12. Some Factors which underlie Susceptibility and 



Immunity to Disease. 



The permanent existence of any species depends upon its 

 capacity for adapting itself to its surroundings. Health and 

 disease in organisms are intimately associated with environ- 

 ment ; and heat, light, moisture, plant foods, etc., are impor- 

 tant factors. An understanding of the optimum conditions 

 necessary for the growth of a plant is of the greatest importance 

 as regards its normal condition of health. The close student 

 of physiology and pathology must always have in mind the 

 perfect type of plant, that is, one possessing perfect health, 

 otherwise his diagnosis may be of little value, and the cause of 



1 Erlenmej'er, Berichte der deutschen Chemiscbcn Gesellschaft, 1877. (Notes by Loew.) 



