REPORT OF THE SECRETARY 113 



amount of chlorophyll present — ^molecule for molecule. That this 

 "intermediate" is probably not free chlorophyll is suggested by experi- 

 ments "wherein the plant was subjected to high light in the absence of 

 carbon dioxide for some time, and then carbon dioxide was suddenly 

 admitted. No pick-up was here observed. Since no photosynthesis 

 occurred in this treatment and no pick-up occurred, it is inferred that 

 the "intermediate" is not formed under these conditions, but is formed 

 during active photosynthesis and makes itself evident by a quick 

 pick-up of carbon dioxide after a previous high rate of photosynthesis. 



The apparatus used in these experiments was satisfactory for de- 

 termining carbon dioxide concentrations below one-half percent. Dr. 

 McAlister is reconstructing this equipment so that it will be suitable 

 for experiments involving concentrations of carbon dioxide as high 

 as 5 percent. With this improvement, he plans to continue his in- 

 vestigation to that of observing light saturation in intermittent illu- 

 mination. Results from such experiments have an important bear- 

 ing on all theories of photosynthesis. 



A great number of automatic records have been obtained during 

 the past year by Dr. Johnston on the recording spectrographic carbon 

 dioxide apparatus. As a result of this work a number of fundamen- 

 tal changes have been made. Dr. McAlister has redesigned and Mr. 

 Fillmen has rebuilt the spectrograph and constructed a new lamp hous- 

 ing for a new infrared emitter designed and made by Mr. Clark. The 

 accuracy of measuring the photographically recorded galvanometer 

 deflections has been increased greatly by superimposing the print of a 

 coordinately ruled plate on the record paper before development. 

 This procedure eliminates the necessity of correcting for changes in 

 size of paper resulting from development. This improvement fol- 

 lowed a suggestion made by Mr. Brj^don. 



Plants respire (give off carbon dioxide) both in darkness and during 

 the process of photosynthesis in light and thus respiration apparently 

 diminishes the intake of carbon dioxide during photosynthesis. 

 Since the absorption of carbon dioxide by the plant is a measure of 

 its photosynthetic activity, it is essential in order to measure photo- 

 synthesis precisely to determine what, if any, direct or indirect 

 changes in respiration take place under the influence of radiation. Is 

 the respiration in darkness the same as it is in light ? Some interest- 

 ing data bearing on this moot question have been obtained both by 

 Dr. McAlister and by Drs. Johnston and Weintraub. 



CHLOROPHYLL FORMATION AND MEASUREMENT 



In any extensive quantitative study of photosynthesis, the role of 

 chlorophyll m^ust be considered. Work already done by Dr. McAlister 

 on the induction phase of photosynthesis provides evidence for the 



