48 CARNEGIE INSTITUTION OF WASHINGTON. 



adjustment of (1) the concentration and quantity of the absorbing barium- 

 hydroxide solution, (2) the length of periods of a single determination, (3) the 

 rate of gas flow, (4) the concentration of the carbon dioxid in the gas stream, 

 and (5) the resistance of the electrolytic cells employed. Similarly, for any 

 series of experiments all of these factors must be properly adjusted to each 

 other in order to determine the degree of accuracy of the set conditions and 

 so as to avoid attempting to attain results which the accuracy of the entire 

 system does not warrant. The work on these methods is being continued, and 

 several new pieces of apparatus have been designed and are being tested. 



Experimental Material. 



The use of entire plants, while desirable in many ways, was found utterly 

 impractical when striving for any degree of precision. It is clearly evident 

 that further insight into the mechanism of the processes of respiration and 

 photosynthesis can be gained only from experimentation, that is, by rigorous 

 control of the external conditions as well as some of the internal factors 

 influencing these processes. Therefore, the studies have been carried out 

 primarily with excised leaves and entire plants have been used only when it was 

 essential to establish the relation of the leaves to the rest of the plant. Besides 

 many other advantages, this method offers the only satisfactory means of 

 feeding to leaves substances the behavior of which it is desired to study. 



It was found that in many plants the gaseous exchange of the photosyn- 

 thetic and respiratory processes is complicated through structural peculiarities 

 of the leaf which make the interpretation of observational data very difficult. 

 For this reason only thin leaves were used. Moreover, experience proved that 

 a rational interpretation of these processes can not be attained without con- 

 siderable knowledge of the internal condition of the leaf. Much attention has 

 therefore been devoted to the elaboration of accurate analytical methods and 

 all of the conclusions are based upon the analyses of the carbohydrate and 

 proteinaceous components of the leaves. It has become clearly evident that 

 without such data a rational interpretation of measurements of the rates of 

 respiration is quite impossible. 



Considerable attention was also given to establishing the length of time 

 necessary to obtain a true respiration curve. Special apparatus was con- 

 structed for the automatic control of the carbon-dioxid absorption vessels. 

 This made possible the carrying out of many experiments, each of about 100 

 hours' duration with a continuous respiration record. 



The Carbohydrate- Amino Acid Relation in the Respiration of Leaves, hy 



H. A. Spoehr and J. M. McGee. 



For some time it has been evident that the rate of respiration, even under 

 carefully controlled external conditions, is greatly influenced by certain inter- 

 nal factors. Besides the carbohydrates, nitrogen compounds which may be 

 present in relatively small amounts have been found to be of profound influ- 

 ence. In order to avoid much of the confusion arising from the consideration 

 of a carbohydrate-nitrogen ratio, special attention was given to the influence 

 of amino-acids in the respiratory process. Thus, it was found that the stimu- 

 lating effect of amino-acids on the respiratory activity and carbohydrate con- 

 sumption of leaves appears to be closely akin to the specific dynamic effect of 



