60 CARNEGIE INSTITUTION OF WASHINGTON. 



The differential action of potassium, sodium, magnesium, calcium, 

 etc., may be taken to be due to the specific action which the salts of 

 these substances exert on the solution of the colloidal material and 

 on colloidal aggregation. 



Some features of plasmolysis and of adaptive reactions of living 

 cells are suggested by the reactions of the colloidal cells filled with 

 water when immersed in a series of salt solutions ranging from 0.001m 

 to 0.008m. The cells in the weaker solutions begin to operate posi- 

 tively and to deliver liquid through the exit tube soon after setting 

 up. Those in the stronger solutions show exosmosis or loss of liquid 

 through the outer wall for the first day, when a reversal takes place 

 and absorption or intake of liquid results from solutions as concen- 

 trated as that indicated by the higher figure given above. A col- 

 loidal cell, which at first shows negative action, then reverses its action 

 and absorbs from the immersion fluid at a certain concentration, 

 may be stepped up to a higher concentration in which it would show 

 loss only if placed in this liquid initially. 



PHOTOSYNTHESIS. RESPIRATION, AND NUTRITION. 



Carbohydrate- Amino- Acid Relation in the Respiration of Leaves, by II. A, 



Spoehr and J. M. McGee. 



In order to pursue the investigations on the carbohydrate economy 

 and respiration of chlorophyllous leaves with greater accuracy and 

 more economy of time, the experimental procedure was modified so 

 as to employ largely electrical methods. The carbon dioxid emitted 

 by the plants was absorbed in solutions of barium hydroxide, and titra- 

 tions were replaced by the determinations of the electrical conductivity. 

 It was necessary to determine the electrical constants of the barium- 

 hydroxide solutions which give the maximum change of resistance per 

 unit change of concentration consistent with the use of such solutions 

 sufficiently concentrated to completely absorb the carbon dioxid in 

 the air-stream. The experimental conditions were so adjusted that 

 concentrations of 0.08 to 0.17 normal barium hydroxide were used. 

 By the employment of suitable devices for the sedimentation of the 

 barium carbonate and special conductivity cells very accurate and 

 rapid determinations of the respiration rates were accomplished. 



The stimulating effect of the amino-acids on the respiratory activity 

 and carbohydrate consumption of leaves has been repeatedly sub- 

 stantiated. Glycocoll, alanine, and asparagin vary in this effect, 

 apparently according to the ease of penetrability. When glucose is 

 given the leaves as the carbohydrate food material this stimulating 

 effect is most marked. With saccharose the effect is also noticeable. 

 With mannose no such reaction could be observed. The experiments 

 with fructose indicate that amino-acids have actually a depressing 



