8 Hydration and Growth. 



the colloid. If dissolved salts are carried by the water, these substances 

 might unite chemically with the material in the molecular aggregates 

 in both the more liquid and the more solid phases of the colloid and 

 cause changes in the water-relations of the mass, or the dissolved sub- 

 stances entering with the water might form adsorption compounds by 

 the uniting in indefinite proportions with the colloidal material in 

 which the water-relations might be changed in another way. Such 

 changes would, of course, be followed by variations in volume. It is 

 to be added that water itself may enter into both relations with the 

 colloidal material and that the initial swelling of a dried colloid prob- 

 ably includes such a chemical combination of water with its molecular 

 aggregates. The action of salts or of acids brought into the mass with 

 water may be such as to carry the dispersion or solvation to the stage 

 in which the mass assumes a liquid condition. 1 



In that type of growth in which carbohydrates or proteins are carried 

 into the mass by water, it may be seen that the accumulation of the 

 additional material in the more liquid phase would by the action of the 

 forces of surface tension result in the aggregation of new masses of 

 material. Such formation of additional elastic gel structure might 

 occur theoretically throughout the entire mass of the cell, but in actual- 

 ity would be modified and controlled at every point by the factors 

 which affect hydration. Aggregation of material in syncretic cavities 

 may be taken to present possibilities of the formation of specialized 

 protoplasmic masses or cell-organs or of secretions. Writers with a 

 keen historical sense may be disposed to see in the conceptions outlined 

 above a modernized statement of the micellar hypothesis of growth of 

 Naegeli, but no great interest may be attributed to any such forced 

 parallelism. 



The measurements described afford a reliable basis for the conclusion 

 that the extent and character of the swelling of gels compounded of 

 carbohydrates and proteins or protein derivatives depends in great 

 degree upon the proportions of the main constituents, not only with 

 respect to pure water, but in solutions of salts and electrolytes in 

 general. The general effect of a salt on hydration depends upon its 

 concentration and whether it is already present in the colloid in chem- 

 ical union or in adsorption with the colloidal material, or whether it 

 enters with the solution or water of hydration ; also upon the character 

 of the salts adsorbed. The extension of the observations upon which 

 these conclusions rest to living cell-masses and to desiccated and dead 

 material from plants demonstrates that colloids may be compounded 

 which may simulate with fair parallelism cell-colloids with varying 

 carbohydrate-protein ratio, salt-content, and acidity. In no feature 

 is this more striking than in the temperature relations. The rate and 

 amount of swelling of plants, and of colloidal mixtures which simulate 



1 Ostwald and Fischer. Theoretical and applied colloid chemistry, p. 101. 1917. 



