STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



69 



It might be argued that this rapid increase in the rate of respira- 

 tion of leaves, which had been previously left in the dark and then 

 given d-glucose, was due simply to the greater available supply of 



Table 51. — Rate of CO2 einission, at S4°, of S leaves of Helianlhus annuus. 

 The excised leaves were placed in a nutrient solution free from organic material and nitrogen 

 and kept in the dark for 42.75 hours. They were then transferred to a nutiient solution con- 

 taining 7 per cent d-glucose and 0.11 per cent glycocoll and the rates of respiration determined. 



sugar. In the experiments already described it has been pointed 

 out that the rate of respiration bears no direct relation to the 

 carbohydrate-supply. There are numerous instances in which an 

 increase of carbon-dioxid emission was obtained with a decreased 

 total sugar-content. In these cases the amino-acids had consistently 



50 



40 



Figure 18. 

 The solid line indicates the rate of re.spiration at 25° of 8 leaves of Helianthus which 

 were kept in the dark for 43.5 hours previous to putting in a nitrogen-free nutrient solu- 

 tion containing 7 per cent d-glucose, as per table 49. The" broken line indicates the rate 

 of respiration at 25° of 8 similar leaves which were kept in the dark for 42.75 hours pre- 

 vious to putting in a nitrogen-free nutrient solution containing 7 per cent glucose and 

 0.11 per cent glycocoll, as per table 50. The ordinate represents mg. CO2 per hour per 

 gram dry material and the absci.ssa the time in hours. 



