STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



47 



In the following experiment the conditions were the same as in 

 the previous one, with the exception that the initial carbohydrate- 

 content was lower and the leaves showed a greater gain in amino 

 acids. The petioles of the excised leaves were also placed in a nitro- 



FlQUBB 10. 



Rate of respiration of 9 leaves of Helianthus annuus at 24°; petiole in 

 nitrogen-free nutrient solution containing 7 per cent of d-glucose, from table 

 23. The ordinate represents mg. CO2 per hour per gram dry material, the 

 abscissa the time in hours. 



gen-free nutrient solution containing 7 per cent of d-glucose, but 

 the leaves also showed no gain in carbohydrate-content. There 

 was, however, a very decided increase in the amino-acids after 

 94.25 hours in the dark. The analytical results are presented in 

 table 24 and the course of respiration in table 25 and figure 11. 



Table 24. 



The noteworthy feature of the foregoing experiment is the very 

 marked drop in the respiration rate during the first 35 hours, and 

 thereafter the decided increase, so that the rate was higher at the 

 end of the experiment than at the beginning. From previous experi- 

 ments, as indicated in table 17, it seems evident that when leaves 

 are placed with the petioles in a 7 per cent glucose solution the carbo- 

 hydrate-content is maintained after the first 24 hours, so that it 

 may be assumed that these leaves, with their initial relatively low 

 carbohydrate-content, did not suffer a decided reduction of this 

 material. It is evident that after about 35 hours the rate of CO2 

 emission increased decidedly, so that at the end of 94.25 hours, in 



