APPENDIX 8 



KEPORT ON THE DIVISION OF RADIATION 

 AND ORGANISMS 



Sm : I have the honor to submit the following report on the activi- 

 ties of the Division of Radiation and Organisms during the year 

 ended June 30, 1936: 



This has been a year of large accomplishment in several fields. Mr. 

 Hoover's work on the dependence of carbon dioxide assimilation in 

 wheat on wave length of radiation has been amplified and rounded 

 out for publication. This pioneering research has produced and 

 checked a curve which gives the efficiency of the different-colored 

 rays to promote photosynthesis. The curve starts at zero in the 

 violet, runs to a maximum in the blue at about 4,400 A, continues of 

 moderate intensity in the green and j-ellow, rises to its highest maxi- 

 mum in the red at 6,500 A, and then falls to zero. 



Dr. Meier has continued her experiments on the effects of ultra- 

 violet rays on algae. Besides checking former work and publishing 

 on lethal effects, she has shown that ultraviolet rays of maximum 

 lethal influence when applied in minute doses are stimulating. This 

 behavior reminds us of the effects of certain poisonous drugs which 

 in minute doses are stimulants. 



Dr. Johnston has continued experiments on the effects of light of 

 different wave lengths to promote growth effects of various kinds in 

 tomatoes. His work has yielded much advance in the technique of 

 these investigations. Among other results which stand out clearly, 

 he finds that rest periods not only from radiation but of diminished 

 temperature are necessary to these plants. 



He gave the annual Arthur Lecture on the subject of the influences 

 of the sun on plant growth. 



Dr. McAlister has developed an extremely sensitive and quick-act- 

 ing spectroscopic method for measuring carbon dioxide concentration. 

 A concentration of 1/10,000 of 1 percent carbon dioxide in air is 

 readily measured. The respiration and carbon dioxide assimilation 

 of a single grain of wheat in its germination is readily observed. 

 Studies of the dependence of photosynthesis in wheat on time factors 

 are in progress and are yielding beautiful and remarkable results. 

 Dr. McAlister also did interesting cooperative work with the Depart- 

 ment of Agriculture on the germination of seeds. 



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