62 CARNEGIE INSTITUTION OF WASHINGTON. 



The Effects of Organic Acids and Their Amino-Compounds on Hydration and 

 Growth, by D. T. MacDougal and H. A. Spoehr. 



The biocoUoids of the plant are pentosan-protein mixtures in which 

 the substances of these two main groups vary widely in their propor- 

 tions, with a smaller proportion of lipins probably more or less localized. 

 The variables are so large that generalizations concerning the action 

 of the plasmatic mass are not easily to be founded. Of the more impor- 

 tant assertions concerning the action of protoplasm, the earliest and 

 most widely used, that protoplasm undergoes hydration like an am- 

 photeric colloid and is exemplified by sweUing gelatine, has long since 

 failed to satisfy the experimental conditions or to offer parallels to the 

 action of cell-masses of the higher plants. 



If protoplasm were entirely or dominantly proteinaceous, the actual 

 acidity or hydrogen-ion concentration might be taken as the chief 

 factor in maintaining the rate and determining the course of hydration 

 and growth. The predominance of the pentosans in plant cells, how- 

 ever, offers a set of conditions much more complex than that of the 

 comparatively simple ionization of gelatine, for, as has been noted, 

 the conditions which facilitate the action of protein gels retard and 

 limit the hydration of the carbohydrate gels to an extent and in a 

 manner which depend upon the structure and character of the pento- 

 sans present. 



The results of Borowikow and of Dachnowski show that the growth 

 of plants, the higher green forms, does not depend upon the hydrogen- 

 ion concentration alone. Acids and bases both influence hydration 

 and growth. In addition, the accelerating effects of amino-acids and 

 amines on hydration of biocoUoids and cell-masses, living and dead, 

 go far to support the conclusion that these substances facilitate or 

 increase total growth. These substances are built up from simpler sub- 

 stances in the plant in a manner which is by no means clear, although 

 under investigation and discussion for a quarter of a century. The evi- 

 dence favors the assumption that they come together in the field of 

 photosynthetic activity. These amino-groups occur only as disinte- 

 gration products of the proteins or albumins in animal metabolism. 



The total amount of amino-compounds in a cell-mass of a plant 

 varies widely during the course of a day, and, as has been noted above, 

 the proportion of nitrogenous material in the organs of the cell or the 

 members of a shoot may be greatly different. 



As the hydrogen-ion concentration of the sap is known to remain 

 fairly constant, as the salts or bases which affect growth also change 

 but slowly, attention naturally focuses on the amino-compounds as a 

 factor in modifying the rate, course, and total amount of growth. As 

 the acids and their salts may be assumed to act invariably in the 

 presence of amino-groups, a series of tests was planned which should 

 make possible a comparison of the action of some of the commoner 

 organic acids and their amino-compounds. 



