III. THE CONSTITUENTS OF BIOCOLLOIDS WHICH AFFECT 

 HYDRATION AND GROWTH. 



Some organs and cell-masses of plants as well as of animals display 

 swelling reactions similar to those of gelatine with respect to acids and 

 salts, and a great deal of discussion of the colloidal action of proto- 

 plasm has been based on the assumption that this parallelism runs 

 throughout. That investigation should have taken this course is 

 natural when it is recalled that gelatine, in common with proteins and 

 many protein derivatives, is amphoteric, and may dissociate either as 

 an acid or as a base, being stronger as an acid than as a base. In a 

 condition of neutrality or at its iso-electric point its hydrogen-ion con- 

 centration is represented by the symbol pH = 4.7. It is to be seen 

 that the diversity of hydration reactions which such substances may 

 display might well give rise to the assumption in question. Further- 

 more, it is to be granted that some organs and cell-masses of animals as 

 well as of plants are so high in nitrogenous compounds as to be charac- 

 terized by the reactions of amphoteric colloids. Thus, for example, bac- 

 teria may contain so much nitrogenous material that the dried remainder 

 obtained from them may appear to consist principally of albumin. 1 



It would be a mistake, however, to assume a close identity of the 

 protoplasmic machine as to its colloidal components. The results 

 described in the present work make it evident that it is a heterogeneous 

 gel, which, in plants at least, is largely composed of inert or neutral 

 carbohydrates of the pentosan group, of which agar, gum arabic, and 

 mucilages are examples. The swelling or hydration of such gels is 

 modified by the action of the proteins, amino-acids, and other nitro- 

 genous substances which may be incorporated with them, but through- 

 out all of my experimentation it was evident that the water-relations 

 of growing plants were more of the character of pentosans than of 

 gelatines. 



Reproductive cells and elements of all kinds may be expected to 

 prove high in nitrogen, and hence would show swelling reactions of the 

 general nature of gelatine. 2 So well is this established that is is pos- 

 sible to predict the main facts as to nitrogen-content upon the basis of 

 a series of swelling tests with distilled water, acids, and alkalies. 



The relation of the nitrogen-content to swelling is well illustrated by 

 some reactions of red algae of the Pacific Coast which were studied at 

 the Coastal Laboratory, Carmel, California, in July and August 1917, 

 by Dr. J. M. McGee. 3 



1 Thompson, D. A. W. Growth and form, pp. 40 and 41. 1917. Cambridge Univ. Press. 



1 Lloyd, F. E. Colloidal phenomena in the protoplasm of pollen tubes. Report Dept. Bot. 

 Research, Carnegie Inst. Wash, for 1917 (Year book No. 16). 1918. 



3 McGee, J. M. The imbibitional swelling of marine algse. Plant World, 21 : 13. 1918. Balti- 

 more. 



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