42 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



marized in table 16, the results of a similar experiment are given in 

 table 17, in which the petioles of the leaves are placed, instead of in 

 nitrogen-free nutrient solution only, in such a solution containing 

 also 7 per cent of d-glucose. Previous to cutting the leaves the 

 plants had been in the sunlight in the greenhouse for about 9 hours. 



Table 16. 



-Analysis of excised leaves of Helianthus annuus kept in the dark ai 

 20°, with petioles in nitrogen-free nutrient solution. 



From the results given in table 17 it is evident, as was shown many 

 years ago by Boehm, that when excised leaves are placed with the 

 petioles in a nitrogen-free nutrient solution containing 7 per cent 

 d-glucose the sugar is taken up into the leaves and accumulates 

 there. As will be seen later at higher temperatures, the sugar under 

 these circumstances accumulates but very little, if at all. However, 



Table 17. — Analysis of excised leaves of Helianthus annuus 

 kept in the dark at 20°, tcith petioles in nitrogen-free 

 nutrient solution plus 7 per cent d-glucose. 



when there is thus an abundant supply of carbohydrates, the amino- 

 acids increase less than in the absence of sugar. The questions 

 which arise, then, are : Do the carbohydrates in any manner influence 

 amino-acid formation, and do the amino-acids affect the rate of 

 carbohydrate consumption by the leaf-cells? Also, what is the 

 influence of light and dark in the formation of amino-acids? The 

 experiments hereinafter described may throw some light on these 

 questions. 



