STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 15 



after longer periods of darkness. He considers that asparagine is 

 used in the leaves for protein synthesis. This is concluded from the 

 smaller quantities of asparagine found in the leaves. 



In our own experiments with germinating beans (see page 40), 

 some in the dark and some in the light, we found but slight difference 

 between the "light" and ''dark" plants. However, these experi- 

 ments were run only 120 hours, while in the investigations of others, 

 already referred to, the analyses were made after periods of 1 to 4 

 weeks. 



The experiments with mature leaves which are described hereafter 

 show clearly that in the dark there is an accumulation of amino 

 acids. This is true not only of the excised leaves but also of those 

 attached to the plant. How intimate a causal interrelationship 

 exists between amino-acid accumulation and carbohydrate depletion 

 it is impossible to state from the experimental data as yet available. 

 This is, of course, an extremely complicated problem, and requires 

 for solution much deeper knowledge of the nature and function of 

 plant proteins than we are now in possession of. This point, how- 

 ever, does become evident, that the amino-acids have a profound 

 influence on the rate of respiratory activity of the leaves, in the 

 sense that an increase in amino-acid content is accompanied by an 

 increase in carbon-dioxid emission and carbohydrate consumption. 



In compendium, then, it appears that in mature leaves: 



1. Amino-acids accumulate in the dark as carbohydrates are consumed. There 

 is some evidence that proteins also diminish in this process. 



2. The rate of carbohydrate consumption is accelerated by amino-acids. At the 

 same time the fact must not be neglected that respiratory activity is a product 

 (within limits) of mass action, the rate depending as one factor upon the supply of 

 available carbohydrates. 



The questions then presented are: In what manner can amino 

 acids influence the rate of respiratory activity? What is the influence 

 of these substances on the general carbohydrate metabolism? Are 

 there any chemical relations between amino-acids and sugar which 

 can account for this behavior, or is this influence exercised through 

 the operation of enzymes? Contributing to the elucidation of these 

 questions are a number of facts which can be drawn from allied 

 sciences. 



Of direct bearing on the question of the influence of amino-acids 

 on the respiratory activity is the phenomenon of the specific dynamic 

 effect of proteins, which, observed in animals, has been the subject 

 of extensive experimental investigation and much controversy. 

 Rubner and others established that, in the diet of animals, fats and 

 carbohydrates are mutually interchangeable on a calorific basis. 

 Thus 100 grams of fat can be replaced by 232 grams of starch and 

 by 234 grams of saccharose. In attempting to apply this principle of 



