SECRETARY'S REPORT 177 



light exposure. Thus the damage is indicated to be mediated not by 

 chlorophyll directly, but through accessory carotenoid pigments in 

 the photosynthetic system. 



In the study of the photoresponses of Phycomyces hlakesleeanus^ 

 detailed action spectra for the growth and tropic responses at high 

 intensities have been completed. Within the visible range, the spectra 

 are identical, indicating that no detectable bleaching of the photo- 

 receptor occurs. It is concluded that direct spectrophotometric 

 measurements for the detection of in vivo changes in the pigment 

 photoreceptor system would be miprofitable. 



Chromatographic and biochemical assays have been made of various 

 compounds extracted from sporangiophores. These compounds in- 

 clude amino acids, reducing and nonreducing sugars, carotenoids, 

 flavins, and various phosphorylated compounds. Dark-grown or 

 light-adapted sporangiophores were exposed to saturating pulse-up 

 light stimuli and assays made at 1-minute time intervals after the 

 stimuli. 



No detectable changes could be observed for carotenoids or amino 

 acids. Significant changes both in quantity and quality of compounds 

 present were observed between adapted and stimulated growing zones 

 for flavins in stage I and IV sporangiophores. Quantitative changes 

 were also observed for reducing sugars. The time course of these 

 changes can be correlated with the observed time course of the light 

 growth response. 



One of the observed flavins, a blue fluorescing unknown, is present 

 in large amoimts in light-sensitive stages of sporangiophore develop- 

 ment and is not found in the light-insensitive mycelia or during for- 

 mation of the yellow sporangium in stage III sporangiophores. The 

 total amount of this material is also a function of the adaptation level 

 of the sporangiophore with the highest concentration occurring in 

 dark-adapted sporangiophores. 



The installation of a carbon-dating laboratory within the division 

 was completed in September 1962, and the dating of a number of 

 archeological samples has been completed. In addition to the service 

 function, the carbon-dating program includes basic research in the 

 techniques of dating by the use of the carbon- 14 method and research 

 employing this method as a tool. 



The innovation of the use of mercury as the principal shielding 

 material in the counting system has been most satisfactory and has 

 resulted in low background levels and high precision. The absolute 

 dates obtained with the mercury system are reliable when compared 

 to those obtained by other laboratories. 



A research project to determine the residence time of water in vari- 

 ous systems was started in October 1962. Preliminary experiments 



