56 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



not maintain the initial rate of CO2 emission and the general course 

 of the rate is down. The rise after 35 hours is very noticeable; this, 

 however, is not maintained and the rate gradually drops. 



Table 35. — Rate of ennssion of CO2 by 6 leaves of Helianihus annuus at 25°. 

 Petioles in nitrogen-free nutrient solution containing 7 per cent sucrose. CO2 absorbed in 

 Ba(0H)2 solution 0.11835 normal, 125 c. c. of which has the CO2 equivalent of 0.3264 gram CO2. 



When, on the other hand, the leaves are given, besides sucrose, 

 a small amount of glycocoU, the course of the respiration rates is a 

 gradual rise. The changes in material are given in the analytical 

 data in table 36. 



Table 36. 



The rates of respiration are given in table 37 and figure 15. From 

 these it is apparent that after an initial drop in the rate of CO2 

 emission, which probably represents the time required for the 

 material in the nutrient solution to migrate into the leaves, there is 

 an irregular rise which becomes pronounced after about 35 hours. 

 The principal difference between the leaves which have been given 

 glycocoU and those without is that in the former there is a marked 

 rise in the rate immediately after the initial drop. This is probably 



