1915.] PUBLIC DOCUMENT — No. 31. 59 a 



2. Study of the optimum conditions of light for plant re- 

 sponse. 



3. Mosaic disease of tobacco and allied diseases. 



4. Influence of electrical stimulation on nitrogen fixation. 



A large amount of data has been gathered in the work on the 

 first project, and results for publication should soon be available. 



Progress on the second project has been largely in the de- 

 velopment of methods and apparatus preliminary to starting in- 

 vestigation of the main problem. 



Investigation of the mosaic disease of tobacco has been under 

 Avay for some time. The completion of the work awaits the 

 result of certain field experiments to be conducted during the 

 present year. The relative activity of enzymes in healthy and 

 diseased plants has been studied in detail during the last six 

 months. Studies are in progress on methods of control, both by 

 inoculation and absorption of chemicals, and on the effects of 

 different lights, and some apparently favorable results have been 

 obtained. These studies are to be continued during the ensuing 

 year. 



Work has begun on the effect of electrical stimulation on 

 nitrogen fixation by Pseudomoims radicicola and Azotohacter, 

 and satisfactory apparatus and methods for accurate work have 

 been developed. The experiment now being conducted deals 

 particularly with the effects of direct current electricity. It is 

 planned to follow this shortly by similar experiments with alter- 

 nating current electricity and with static charges. The maxi- 

 mum and minimum currents have been determined more or less 

 satisfactorily. 



The results of investigation on electrical injuries to trees, 

 which had extended over a number of years, were published in 

 October as Bulletin No. 156. 



