PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 4 APRIL 15, 1918 Number 4 
DYNAMICAL ASPECTS OF PHOTOSYNTHESIS 1 
By W. J. V. Osterhout and A. R. C. Haas 
Laboratory of Plant Physiology, Harvard University 
Communicated by G. H. Parker, February 7, 1918 
Although a great amount 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 4 that even under favorable con- 
ditions 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, 
consisting of thin layers or filaments, whose temperature can be regulated 
to a sufficient extent for the purposes of the investigation. 
The fronds of the marine alga, Ulva rigida (sea lettuce), are so suitable for 
this purpose that most of the experimental work was confined to them, al- 
though 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 tem- 
perature remains very close to that of the surrounding liquid. A further 
advantage of thin fronds is that gaseous exchange is extremely rapid. 
To obtain data for the study of dynamics, it is necessary to determine at 
frequent intervals how much photosynthesis has taken place. This was ac- 
complished by a method elsewhere described. 2 This method enables us to 
measure quickly and accurately the amount of photosynthesis at definite 
intervals, without subjecting the plants to an abnormally high concentration 
of CO2 as has heretofore been customary. 3 It depends upon the fact that 
photosynthesis abstracts carbonic acid from the surrounding solution and 
renders it more alkaline. By the use of indicators the degree of alkalinity, and 
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