100 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



mittee which comes under the National Defense Research Committee. 

 He also represents the Institution as a technical adviser to the Navy 

 with reference to emergency rescue equipment, which section is now 

 under the United States Coast Guard. 



The termination of this emergency work has permitted the resump- 

 tion of the Division's regular research program. Two of our labo- 

 ratory rooms have been equipped with apparatus and facilities for 

 the continuation of our studies on photosynthesis and on the wave- 

 length effects of light on growth. It has been found necessary to 

 rebuild much of the C0 2 measuring apparatus and to carry out exten- 

 sive tests before our fundamental problems could be taken up. These 

 steps are now in process of completion, and four preliminary experi- 

 ments on wave-length balance and plant growth have been carried 

 out. Two other general problems have been pursued: (1) Influence 

 of light on respiration of the grass seedling, and (2) course of devel- 

 opment of the grass seedling as influenced by environmental factors 

 with special attention to the role of radiant energy. 



It has been noted previously (Weintraub and Johnston, 1944) that 

 brief illumination of etiolated barley seedlings resulted in a marked 

 increase in rate of carbon dioxide evolution. In attempting to gain 

 information on the mechanism of this effect a study has been made of 

 the reducing sugar content of the plants as influenced by light; no 

 significant change in sugar content was found under the experimental 

 conditions employed. In the course of this work it became necessary 

 to devote considerable time to a study of methods of sugar analysis as 

 applied to plant tissues; some of the findings have been published. 

 Experiments are now in progress on measurement of oxygen consump- 

 tion concurrent with the carbon dioxide production. 



The investigation of grass seedling development has proceeded along 

 several lines. In addition to effects of radiation itself, a study is being 

 made of the role of some other environmental factors such as tempera- 

 ture, nutrient supply, and aeration. Additional data have been ob- 

 tained regarding the action spectrum of mesocotyl inhibition in oats 

 over a wide range of light intensities; at low intensities a second maxi- 

 mum occurs in the neighborhood of 620 m/i. It is hoped that work on 

 the isolation of the photoreceptive pigments can be resumed shortly. 

 Comparison of the effectiveness of red and of violet light has been 

 made for several other species representing a majority of the tribes of 

 grasses ; the responses of all species have been found to be fairly similar 

 to that of Arena, thus greatly extending the generality of the earlier 

 results of Weintraub and McAlister (1942). The influence of light 

 on elongation of the grass coleoptile also is being studied; the results 

 to date have demonstrated a marked effect of temperature on the 

 response of this organ to light which causes inhibition at lower tem- 

 peratures but an apparent stimulation at higher temperatures. 



