14 



Hydration and Growth. 



any given line have been obtained under identical conditions. One of 

 these comparative series made in 1916 may be cited as an example of 

 the relative behavior of agar and gelatine to water, acids, and alkalies. 



TABLE 2 1 . 



The next departure in the experimentation was to make a mixture 

 of these two substances as representing the carbohydrates and proteins 

 of the plant, and this was done in a series of plates in which the two 

 elements entered in proportions from 1 or 2 to 9 parts in 10. The 

 diverse results which were obtained gave ample promise of affording 

 many useful comparisons with the action of plants. 



It was, of course, not taken for granted that the ammo-acids used 

 duplicate those which are found in the plant or that such compounds 

 afforded all of the more important factors affecting water-relations. 

 The next step in the making of a colloidal mixture which might imitate 

 the action of the plant in relation to water was to use various albumin- 

 ous compounds to furnish the nitrogenous element in the biocolloids. 



According to Beijerinck and others, combination of agar and gelatine 

 or gelatine and starch in a 10 per cent solution would result in a simple 

 admixture of the colloidal masses of the two substances in the form of 

 minute masses or strands. 2 Such mixtures would be more intimate and 

 present greater surfaces than those made up from the powdered mate- 

 rial brought together with little water and at low temperatures. Pro- 

 gressively finer subdivision of the materials and more perfect dispersion 

 would finally reach a point near the limits of gelation where the sub- 

 microns of agar and starch, for example, might come together in the 

 walls or fibers and in the more liquid part of the two-phase system of 

 colloids, and the substances in the parts remaining to fill cavities or 

 vacuoles might be in various groupings, according to one view. On 

 the other hand, very weighty theoretical considerations lead to the 

 conclusion that the relations of the carbohydrate-protein substances 

 in such a system would be determined quantitatively. Thus a mixture 

 of 8 or 9 parts of agar and 1 or 2 parts of gelatine or albumin at a high 

 degree of dispersion would be followed by a gelation in which the pre- 

 dominating substance, agar, would form the external or continuous 



1 MacDougal, D. T. Imbibitional swelling of plants and colloidal mixtures. Science, 44 : 502. 

 1916. 



2 Beijerinck, M. W. Ueber Emulsoidcnbildung bei der Vermischung wasseriger Losungen 

 gewisser gelatinierendern Kolloide. Zeitsch. f. Kolloid-Chem., 7 : 16. 1910. 



