92 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



After the leaf had been in the dark for 75 hours, the rate of respi- 

 ration was 0.0022 mg. CO2 per square centimeter per hour. During 

 the subsequent 2 hours of photosynthesis the leaf fixed 0.0054 mg. 

 CO2 per square centimeter per hour. Thereafter the rate of photo- 

 synthesis rose, and after 86.41 hours the rate of respiration had also 



il 



_r 



Figure 24. 

 Rates of respiration and photosynthesis of an excised leaf of Canada 

 Wonder bean kept in the dark 64 hours previously, as per data given in table 53. 

 The values above the zero line indicate rates of photosynthesis; those below, 

 the rates of respiration. The ordinates represent mg. CO2 fixed and emitted 

 per sq. cm. per hour X 10; the numbers of each square correspond to the periods 

 as given in table 54. 



risen to 0.0034 mg. CO2 per square centimeter per hour. Apparently 

 the carbohydrate-supply had been increased through the photosyn- 

 thetic activity. During the next periods of exposure to light the 

 photosynthetic rate continued to rise, and the final period of respi- 

 ration shows a considerably higher rate. The photosynthetic rates 

 are in each case calculated by subtraction from the last preceding 

 respiration period. This undoubtedly accounts for the relatively 

 low values of the last photosynthetic period (Nos. 9 and 14), for 

 the leaf was at this time emitting carbon dioxid at a higher rate 

 than during the last respiration period. If the last photosynthetic 

 rates were calculated from the first succeeding respiration period, 

 the rate of the former would result considerably higher. This fact 



