56 Hydration and Growth,. 



freezing, and finds that the principal effect is an increase in the hydro- 

 gen-ion concentration followed by a general return to original values 

 on thawing, with changes in the proteins generally consisting in pre- 

 cipitations of some of the proteins.^ 



The results of Borowikow and those of Dachnowski show that the 

 growth of the higher green plants, 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, Uving and dead, 

 go far to support the conclusion that these substances facilitate or 

 increase total growth. These substances are built up from simpler 

 substances in the plant in a manner which is by no means clear, al- 

 though under investigation and discussion for a quarter of a century. 

 The evidence favors the assumption that they come together in the 

 field of photosjTithetic activity. The structure of these amino- 

 groups may be no means be assiuned to be identical with that of the 

 amino-acids of animal metabolism, in which they occur only as dis- 

 integration products of the proteins or albumins. 



The total amount of amino-compoimds 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-compoimds 

 as a cause 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 were planned which should 

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

 organic acids and their amino-compounds. 



Two groups were chosen for the tests — succinic acid and its amino- 

 compound, amino-succinic or aspartic acid, which are dibasic; and its 

 amide, as noted above, which is monobasic; and acetic acid and its 

 amino-compound, glycocoU, which are monobasic. Sections of plates 

 of agar, gelatine, agar-gelatine, agar-protein, and other mixtures were 

 used. Swellings were carried out in the equable chambers of the 

 Coastal Laboratory, at 15° to 16° C. The principal results are given 

 in table 45. 



The two organic acids, succinic and acetic, are seen to exert the 

 classical effect on gelatine, the greatest hydration taking place in the 

 higher concentrations, the effect decreasing with dilution until at 

 0.0004 N the swelling in acetic acid was scarcely greater than in dis- 

 tilled water. At 0.0004 M, however, the dibasic succinic acid showed 



' Harvey, R. B. Hardening procesees in plants and developments from frost injury. Jour. 

 Agric. Res., 15: 83. 1918. 



