72 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



PHOTOTROPISM 



Phototropic investigations previously reported have been carried 

 further into the blue end of the spectrum. It has been found that 

 a maximum is reached at 4,500 A., the phototropic response drop- 

 ping off rapidly then as one proceeds to 4,000 A. The results of the 

 investigation at this stage were reported by Doctor Johnston to 

 the American Society of Plant Physiologists at New Orleans in De- 

 cember of this year. Later experiments have indicated that de- 

 partures from a simple curve, rising to a maximum and falling off 

 again, are present. Further research is being carried on in order 

 to determine whether fine structure may be present which would 

 have an interesting bearing upon the theory of phototropism. 



ULTRA-VIOLET 



Ultra-violet measurements of the mercury arc with the double 

 monochromator previously reported have been carried to the point 

 where absolute intensities can be determined with reasonable cer- 

 tainty. The results of this investigation are in the process of pub- 

 lication by Doctor McAlister. 



COOPERATION 



Cooperative work with the Department of Agriculture has been 

 greatly advanced by the appointment to their staff in the Bureau 

 of Plant Industry, under Dr. Walter T. Swingle, of Dr. Lauriston 

 C. Marshall. Doctor Marshall is working closely with this division 

 upon their problems in determining the effects of radiation upon non- 

 competitive crop plants. Doctor Marshall is a physicist with special 

 qualifications in the fields of photoelectricity and electrical conduc- 

 tivity through gases. The division has profited greatly by his asso- 

 ciation, as his experience supplements that of the physicists of the 

 division, whose line of work has been chiefly in spectroscopic fields. 



Continued cooperation with the Fixed Nitrogen Research Labora- 

 tory has made possible convenient exchange of facilities. Arrange- 

 ments have been made with the Westinghouse Laboratories for the 

 exchange of thermocouples and photocells, which will greatly facili- 

 tate our ultra-violet work. 



Respectfully submitted. 



F. S. Brackett, Chief 



Dr. C. G. Abbot, 



Sea^etary, Smithsonian Institution. 



