APPENDIX 8 



REPORT ON THE DIVISION OF RADIATION AND 

 ORGANISMS 



Sir: I have the honor to submit the following report on the activities 

 of the Division of Radiation and Organisms during the year ending 

 June 30, 1934: 



The work of the year has been very fruitful. It was supported as 

 heretofore largely by a special grant from the Research Corporation of 

 New York. There has been no change in personnel excepting the 

 resignation of Miss Virginia Stanley, typist secretary, and the substi- 

 tution, part time, of Miss Ruth MacManus. 



Most of the experiments of the Division are done with electric lights. 

 Mr. Hoover continued measurements on the absorption of carbon 

 dioxide from the air by wheat plants under the influence of radiation. 

 Using the Christiansen filters prepared by Messrs. McAlister and Clark 

 as described in last year's report, Mr. Hoover was able to grow wheat 

 in rays comprising narrow bands of nearly homogeneous radiation of 

 various wave lengths between the ultraviolet and the infrared spectral 

 regions. These rays were of measured intensity; the temperature, 

 humidity, and chemical food of the plants were standardized ; and the 

 absorption of carbon dioxide was recorded by automatic apparatus. 

 The results obtained were checked by growth experiments under 

 strictly monochromatic rays produced by the mercury arc. 



As a result a well-determined curve of photosynthesis, rising from 

 zero in the ultraviolet, reaching maxima at about 4400 and 6400 

 angstroms, and descending to zero in the infrared, has been deter- 

 mined. 



Dr. McAlister assisted Mr. Hoover and the other members of the 

 staff in many physical manipulations, standardizations, and measure- 

 ments. He also, in cooperation with Dr. Wright, of the Department 

 of Agriculture, carried through a long series of measurements on the 

 effect of radiation on worm eggs. He also worked out for Director 

 Abbot the elements of a set of Christiansen filters covering the region 

 3300 to 10300 angstroms for use in stellar spectrum measurements at 

 Mount Wilson. With Dr. F. S. Brackett he made much progress in 

 the development of powerful apparatus for visible and infrared absorp- 

 tion spectral investigations. 



Dr. E. S. Johnston, besides having immediate charge of the Divi- 

 sion, conducted growth experiments with special radiation on toma- 



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