SECRETARY'S REPORT 97 



0.15 mm. away from the sporangiophore, and with its long axis paral- 

 lel to the axis of the sporangiophore, produced negative curvatures. 

 All experiments were performed in a water-saturated atmosphere in 

 order to prevent negative avoidance responses due to the proximity of 

 the lens. The data support Buder's conclusion that the focusing ad- 

 vantage is the principal effect which produces the light gradient nec- 

 essary for phototropism. Wlien compared to data obtained from 

 sporangiophores immersed in inert liquid fluorocliemicals, the attenu- 

 ation across the growing zone appears to be of the order of 10 percent. 

 Therefore, for blue stimuli, under any irradiation conditions in which 

 the focusing advantage is less than 10 percent, negative curvatures are 

 produced by unilateral stimuli. 



Preliminary observations were made of the growth rates of sporan- 

 giophores at intensities greater than 1,5 milliwatt/cm.^, for which 

 phototropic indifference occurs with unilateral stimuli. It was found 

 that the growth rate increased markedly for these high intensities 

 from the normal adapted level of 3-4 mm./hr. to 5-6 mm./lir. and was 

 maintained at this high level for several hours. 



Instnnnents for measuring the spectral distribution of sunlight in 

 six wavebands from 250 m/x to 5,000 m/x were completed and mounted 

 on the roof of the North Tower of the Smithsonian Building. Auto- 

 matic recorders have been installed on the tenth floor of the Tower 

 and measurements are being made continuously from an hour before 

 sunrise to an hour after sunset. 



PUBUCATIONS 



SisLEB, Edwabd C, and Klein, Whxiam H. Effect of red and far-red irradia- 

 tion on nucleotide phospliate and adenosine triphosphate levels in dark-grown 

 bean and Avena seedlings. Physiologia Plantarum, vol. 14, pp. 115-123, 1961. 



Shbopshibe, W., Jr. ; Klein, "W. H. ; and Elstad, V. B. Action spectra of 

 photomorphogenic induction and photoinactivation of germination in Arabi- 

 dopsis thaliana. Plant and Cell Physiol., vol. 2, pp. 63-69, 1961. 



OTHER ACTIVITIES 



During the course of the year, members of the staff attended a num- 

 ber of national and international scientific meetings. Dr. W. H. Klein 

 traveled to the International Photobiology Congress in Copenhagen, 

 Denmark, and was one of the United States representatives at the 

 Seed Irradiation Conference in Karlsruhe, Germany. He also visited 

 a number of laboratories in Denmark, Germany, and the Netherlands. 

 Members of the staff who were present at the annual meeting of the 

 American Institutes of Biological Sciences in Stillwater, Okla., were 

 Dr. L. Loercher, L. Price, and Dr. E. C. Sisler. Papers from the 

 Division included in the program of this meeting were : "Chlorophyll 

 Synthesis in X-irradiated Etiolated Bean Leaf Tissue," by L. Price 

 and W. H. Klein, and "Effect of Red and Far-red Irradiation on 



