80 CARNEGIE INSTITUTION OF WASHINGTON. 



activities in the oxidation of hydrogen, hydrogen sulphide, methane, 

 etc., Hberate relatively enormous quantities of energy and are thus 

 capable of fixing the carbon dioxid of the atmosphere without the 

 action of radiant energy. 



Carbohydrate Supply and Respiration, by H. A. Spoehr. 



Prerequisite to a rational study of the effect of various conditions 

 on the respiratory activity of leaves is more precise knowledge of the 

 nature of the normal course of respiration. This information is, of 

 course, also essential in application to the study of photosjTithesis, 

 as has been already indicated. An extensive series of experiments 

 planned to determine the rate of carbon-dioxid emission was carried 

 out by the use of leaves cut from the plant and seedlings growing in 

 various nutrient solutions. A mercury-seal respiration chamber has 

 been devised which greatly facilitates working with various plants at 

 constant temperatures. 



When a leaf with an abundant supply of carbohj^drates is kept in 

 the dark at constant temperatures, e. g., 24°, the rate of carbon-dioxid 

 emission falls steadily as the carbohydrate-content diminishes. 



If a leaf, the carbohydrate-content of which is almost exhausted, 

 is placed with the petiole in a 5 to 10 per cent dextrose solution, the 

 carbohydrate-content of the leaf again rises. The carbon-dioxid 

 emission, however, does not show a corresponding increase with the 

 augmented sugar-supply, but increases a little and then continues to 

 fall. Experiments have been directed to determine the conditions or 

 substances necessary for regaining or maintaining the original higher 

 rate of respiration. 



The possible influence of various mineral nutrients was tried out by 

 studying the effect of a series of solutions prepared on the basis of 

 Shive's investigations. The effect of three components was tested — 

 nitrate, potassium, and magnesium. At the present stage of the 

 investigation it seems doubtful whether any definite information 

 regarding the role of mineral nutrients in respiration can be gained 

 from these experiments. 



Other experiments were directed toward increasing the amount of 

 protein in the leaves. With nitrates supplied, and when the nutrient 

 solution contains 10 per cent dextrose, the leaves are capable of syn- 

 thesizing proteins in the dark. Under such conditions the reduced 

 rate of respiration was somewhat increased, but also only shghtly. 

 The most promising results w^ere obtained with combinations of 

 monosaccharides and amino-acids in the nutrient solution. It is, 

 however, still an open question in w^hat manner these combinations 

 operate; that is, whether they directly influence enzyme action or in 

 such a manner as to produce favorable conditions of solution {e. g., 

 the hydrogen-ion concentration) within the protoplasmic complex. 



