64 CARNEGIE INSTITUTION OF WASHINGTON. 



d-glucose and glycocoll the primary reduction in the rate of carbon- 

 dioxid emission, noted above under 2, is very sHght, and the rate then 

 rises gradually. 



In general, then, the rate of carbon-dioxid emission of leaves is in- 

 fluenced not only by the amount of available carbohydrates, but by 

 other complemental factors as well. Amino-acids exercise a stimu- 

 lating effect on the respiratory activity of leaves. Thus, in order to 

 maintain the respiratory activity at an approximately definite rate, the 

 effect of decreasing or low carbohydrate content which results in a 

 lowering of the respiration-rate (probably purely on the basis of the 

 law of mass-action) can be counteracted by an increase in the amino- 

 acid content. Similarly, high sugar and high amino-acid content 

 result in a very high respiration-rate. However, it is apparently not a 

 simple mathematical ratio between the carbohydrate and the amino- 

 acid content which governs the rate of respiration. 



Interrelation of Photosynthesis and Respiration, by H. A. Spoehr. 



The experiments with this subject have been continued and some- 

 what elaborated with more precise apparatus and through a larger 

 range of conditions. The principles as outhned in the annual report of 

 last year have been substantiated. The respiratory activity of a 

 chlorophyllous leaf affects fundamentally the rate of photosynthetic 

 fixation of carbon dioxid. This relation of respiration and photo- 

 synthesis is, moreover, one of very delicate adjustment. Whether this 

 relation is a purely chemical one or, as has been h3rpothesized, involves 

 the fundamental energetics of the plant has not been definitely estab- 

 lished. Under conditions of low energy-release through respiration 

 photosynthetic activity is also reduced. WTien the leaf is deprived of 

 oxygen and thus consumes its food material of anaerobic respiration, the 

 amount of energy released is notably much lower than under the 

 natural, aerobic conditions. Of great importance is the fact, which has 

 been substantiated recently by both Warburg and Willstaetter, that 

 under anaerobic conditions photosynthetic activity ceases. Under 

 these conditions no intensity of light will bring about the reduction of 

 carbon dioxid. 



It has, therefore, been necessary to undertake a more searching 

 study of the factors influencing the respiratory activity of leaves, with 

 special attention to internal conditions affecting the energy-release and 

 with the aim of coordinating the results thus obtained with similar 

 experiments on the photosynthetic activity. 



Reduction and Dehydration of Pentose Sugars, by H.A. Spoehr and 



J. W. E. Glattfeld. 



Physiological-chemical investigation of plant metabolism has been 

 directed in the main towards a study of the catabolic processes taking 

 place in the living organism. These processes are, in general, in the 



