64 Hydration and Growth. 



alone gives an average swelling of about 2,600 per cent of plates 0.18 

 to 0.20 mm. in thickness at 13 C. When combined with gelatine in 

 proportions of 8 to 2, the swelling is less than 1,700 per cent. 



The reactions of the pentosans and pentosan-protein colloids in 

 solutions of the ammo-compounds show some highly important depart- 

 ures, the chief of which is the fact that the hydration capacity is 

 greater than in distilled water in such monobasic acids, but not in the 

 dibasic aspartic acid. This last-named substance dissociates, so that 

 .01 M, pH = 3, in accordance with which it is found to lessen the 

 hydration capacity of agar, but, on the other hand, this action is not 

 shown by the pentosan-protein mixture. No explanation may be 

 offered for this behavior and for the excessive swelling of pentosans 

 and pentosan mixtures in amino- compounds, except that amino-com- 

 pounds may form salts with the carbohydrate, thus increasing the 

 hydration capacity of the latter. That this superior swelling is an 

 actuality is well demonstrated by the increase that resulted when agar- 

 albumin sections in a condition approaching complete hydration showed 

 a further marked increase wlien the water was replaced with an 

 asparagin solution. The positive action of the amino-compounds is 

 also well demonstrated by the fact that the maximum effects were 

 produced at a concentration not coincident with the maximum con- 

 centration and at a point of great dilution. 1 



When these results are applied to the conditions in the cell, emphasis 

 is given to the fact that the total of amino-acids is always no more than 

 a fraction of the amount of organic acids present. It is highly probable 

 that these substances, originating constructively in the plant and 

 affecting growth in a profound manner, may do so partly by their 

 participation in the buffer processes. 



1 MacDougal and Spoehr. The effect of organic acids and their amino-compounds on the 

 hydration of agar and on a biocolloid. Proc. Soc. Exper. Biol. and Med., 16: 33. 1918. 



