STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



97 



preceding respiration rate. For this reason the last photosynthesis 

 period, No. 7, appears low. Calculated on the basis of the next 

 following respiration rate, which represents more nearly the true 

 condition, the photosynthesis rate would be 0.0523 instead of 0.0413 

 mg. CO2 per square centimeter per hour. 



Table 57. — Rates of respiration and photosynthesis of a leaf of Helianthus anyiuus. 

 The CO2 concentration was 15.5 times that of atmospheric air, temperature 24°; light 1,740 

 lux; area of leaf, 120.81 sq. cm. The air-stream equals 9.98 mg. CO2 per hour. 



In the experiments described under 2, 3, and 4, the decrease in 

 photosynthetic activity occurs after the leaves had remained in the 

 dark for more or less prolonged periods. The possibiUty naturally 

 suggests itself that the reduction might be due to a decrease in the 

 chlorophyll of the leaves, caused by keeping the plants in the dark. 

 On the basis of the investigations of Willstaetter and Stoll,» it is highly 

 improbable that this is the case. They kept leaves in the dark at 

 34° to 37° for 48 hours, and although, toward the end of this period, 

 there were evidences of protoplasmic disturbances (abnormally high 

 CO2 evolution), the determinations of the chlorophyll components 

 at the end of the period gave the same results as normal leaves. 



It is doubtful whether there exists between the respiratory and 

 photosynthetic activities anything like a fixed or quantitative ratio. 

 The quotients determined by Pelster, after all, represent rather con- 

 fined conditions. Similarly, we found that with atmospheric air the 

 quotients are about of the same magnitude as those found by Pel- 

 ster. With increasing carbon-dioxid content, however, the quanti- 

 tative relation of these values changes, although the relative magni- 

 tude seems to indicate an interrelationship. Moreover, this inter- 

 relationship appears to be of a more intricate nature than if it were 



Willstaetter, 

 p. 36. 



R., and A. Stoll. Untersuchungen ueber die Assimilation der Kohlensaeure, 



