V. THE EFFECTS OF ORGANIC ACIDS AND THEIR AMINO 

 COMPOUNDS ON HYDRATION AND GROWTH. 



The biocolloids 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 im- 

 portant assertions concerning the action of protoplasm, the earliest 

 and most widely used, that protoplasm undergoes hydration like an 

 amphoteric colloid, and is exemplified by swelling gelatine, has long 

 since failed to satisfy the experimental conditions or to offer parallels 

 to the action of cell-masses of the higher plants. 



It obviously follows that the assumption adopted by many writers 

 that any conditions which facilitate the ionization of the proteins 

 accelerate growth is not tenable, since the effect of acidity is to lessen 

 hydration of the pentosans or pentosan mixtures or cell-masses when 

 acting directly or in the presence of salts. The extensive use of agar 

 to represent the pentosan element in biocolloids in my experiments 

 does not imply that this substance or any other body presenting all 

 of its main physical characters are invariably present in the cell. The 

 gums from acacia, tragacanth, Opuntia, and from Prosopis and the 

 cherry-tree in all probability represent types of pentosans which may 

 really be the most abundant in plants. These gums or mucilages are 

 readily dispersible and have an indefinite hydration capacity which 

 soon passes beyond the limits of measurement by the auxograph 

 Their water-absorbing capacity would be none the less important, 

 when inclosed in the cell-sacs. The solubility of protoplasm has 

 formed the subject of some discussion among cytologists, and it would 

 seem highly probable that valid observations of both extremes may 

 have been made, the matter depending chiefly on the nature of the 

 pentosan, gum, or mucilage which entered into the plasmatic colloids, 

 together with the character of the more liquid phase, or the cell-sap. 



The conclusions of Loeb^ to the effect that it is not possible for an 

 amphoteric colloid to be acted upon by both ions at the same time, 

 if correct, would add still further proof to the fact that protoplasm 

 does not behave like an amphoteric colloid in its hydration relations, 

 except in so far as it may be predominantly composed of such material. 



Data for a critical review of this matter are not available at present, 

 but it is known that bacteria are high in albumin, and similar richness 

 of proteins is exhibited by fungi, and that certain algse show a large 

 proportion of amino-acids. In addition, proteins are abundant in 



* Loeb, J. Amphoteric colloids. Chemical iafluence of the hydrogen-ion concentration. 

 Jour. Gen. Physiol., 1 : 39. 1918. 



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