8 



DYNAMICS OF PHOTOSYNTHESIS 



day. It was found that if the work was done between 9 a.m. and 4 

 p.m. the changes in the intensity of the sunlight might be neglected. 



The results obtained are given in Table I, which represents the 

 average of five experiments, and are illustrated in Fig. 1 . 



It is evident from Fig. 1 that the rate increases rapidly at first, 

 then more and more slowly until it finally ceases to increase. From 

 this point onward a steady rate is maintained.^^ The result is sur- 

 prising, but in view of the fact that it has been confirmed by numerous 

 experiments with Ulva as well as by experiments on Enter omorpha, 

 Spirogyra, Hydrodictyon, Potamogeton, and other plants^'' it seems to be 

 well established. 



TABLE I. 



Average of five experiments at 27°±0.5°C. 



Two questions of great interest now present themselves. First, 

 why does the rate increase at the start?^^ Second, why does it finally 

 become stationary? 



' ^2 This steady rate is not the same for each piece of frond but each piece is fairly 

 constant in its rate, so that if the material is kept over night it will be found the 

 next morning that different pieces may start out at different rates, but the steady 

 rate which each piece finally attains is practically the same as the steady rate 

 which the same piece had the day before. In fact it is possible to recognize the 

 various pieces by this means. 



^' In experiments on fresh water algae a small amount of sodium bicarbonate 

 was added to the water. 



^* This acceleration is not due to the increase in the intensity of light as the sun 

 gets higher for it was also observed when the experiments were started at noon. 



