STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



41 



With mature excised leaves kept in the dark the change in amino- 

 acid and carbohydrate content naturally becomes much more 

 marked. Thus in table 16 are given the results of analyses of an 

 experiment in which 40 similar leaves of about the same age and size 

 were cut from plants. These plants had been exposed to sunUght 

 in the greenhouse for about 9 hours. The cut leaves were placed 

 in battery jars, with petioles in nitrogen-free nutrient solution, and 

 kept in the dark; every 24 hours 8 leaves were removed and analyzed. 



The results given in table 16 show a decided and regular decrease 

 in the carbohydrate-content of the leaves kept in the dark. Also, 

 the amino-acids in these leaves increased with continued time in 

 the dark, although there was no inorganic nitrogen given in the 

 solution. It would appear, therefore, that there is a continuous 

 formation of amino-acids, presumably from proteins, and that under 

 these conditions the rate of protein decomposition exceeds the rate 

 of protein synthesis, with the result that the splitting products in 

 form of amino-acids accumulate in the leaves. The effect of this 

 process on the rate of respiration and its relation to the carbohydrate 

 economy of the plant can in part be gathered from the following 

 experiments. 



In table 16 were also given the results of analyses of leaves kept 

 in the dark and showing the gradual depletion of the carbohydrate 

 material used by the plant as material from which it derives its 

 energy. The course which the rate of respiration follows under 

 these circumstances has been described in figure 8. These phenom- 

 ena are of fundamental importance and appear relatively simple 

 and well known. The fate and behavior of the proteins under Uke 

 circumstances are, however, quite obscure. Furthermore, it is 

 impossible and irrational to try to follow the fate of these substances 

 in plant respiration without simultaneously considering the car- 

 bohydrate economy. As a counterpart to the experiment sum- 



