ON THE DYNAMICS OF PHOTOSYNTHESIS. 



By W. J. V. OSTERHOUT and A. R. C. HAAS. 



{From the Laboratory of Plant Physiology, Harvard University, Cambridge.) 



(Received for publication, July 8, 1918.) 



Although a great deal of attention has been paid to photosynthesis, 

 nothing is known of the dynamics of the process. This aspect of the 

 matter especially deserves investigation as furnishing a new point of 

 attack upon this difficult problem. 



We cannot analyze the dynamics of photosynthesis without first 

 securing accurate data. A preliminary difficulty lies in the control 

 of temperature; when leaves of land plants are exposed to sunlight, 

 changes of temperature at once take place in the leaf and it is found 

 that even under favorable conditions of control the temperature of 

 the leaf may fluctuate as much as 10°C. in a half hour period. To 

 avoid this difficulty, the writers have employed certain aquatic plants, 

 which form thin layers or filaments, whose temperature can be regu- 

 lated to a sufficient extent for the purposes of the investigation. 



The fronds of the marine alga, Ulva rigida (sea lettuce), are so useful 

 for this purpose that most of the experimental work was confined to 

 them, although other material was used for comparison. These 

 fronds consist of only two layers of cells and are so thin (about 0.078 

 mm.) that their temperature remains very close to that of the sur- 

 rounding liquid. A further advantage of thin fronds is that gaseous 

 exchange is extremely rapid. 



The experiments on Ulva were carried on at the Marine Biolog- 

 ical Laboratory at Woods Hole during the month of August 

 when an abundant supply of excellent material was available. 



To obtain data for the study of dynamics it is necessary to deter- 

 mine at frequent intervals how much photosynthesis has taken place. 

 None of the available methods was satisfactory for our purpose. 

 The method of counting bubbles is open to serious objections while 

 the method of analyzing the gases in solution, as developed by Black- 

 er. 1 • . 





