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AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
fluenced by amino acids. It may be that there are two essentially different 
substances in protoplasm, one more viscous than the other, and that various 
substances are distributed in these two media as non-living inclusions. It 
is also possible that living protoplasm exists in only small quantities in any 
cell, while the greater share of the substance now termed protoplasm is 
composed of products of the cell enzyms; products which are themselves 
non-living, but which, because they may change their colloidal state readily, 
may often appear as the conspicuous part of the entire system. Coagulation 
and variations in viscosity observed in “ protoplasm ” might thus be due to 
colloidal changes in non-living inclusions. Whatever value these sugges¬ 
tions may have, the data are at present insufficient to decide between them. 
Irrespective of just what it is that coagulates, coagulation is a sign that the 
cell is becoming more inactive. For the descriptive purposes of this paper, 
“protoplasm” will be considered to mean the entire visible colloidal com¬ 
plex. It varies in viscosity from a sol to a stiff jelly, and it contains or is 
associated with proteins, carbohydrates, fats, lipoids, and salts, in unknown 
combinations. Because it can form jellies, and because more than a trace 
of electrolyte is required to precipitate it, it is classified with the emulsoids. 
The part that is played by the surface layer of a protoplast in determining 
the permeability of protoplasm is not known. By some writers it has been 
regarded as a membrane of peculiar composition; by others as merely a con¬ 
densation film of protoplasm, differing from the interior of the protoplast 
in its surface-tension qualities. Of course the latter hypothesis cannot 
hold, for the Gibbs-Freundlich law, which states that substances that lower 
the surface tension of a system become more concentrated at the surface, 
and that substances that raise the surface tension become more concen¬ 
trated in the interior, applies to solutions only. Protoplasm is obviously 
not a solution, and we have no knowledge of the laws that govern the 
distribution of substances in a heterogeneous, colloidal system. Whatever 
the nature of the surface layer may be, it is to be remembered that it is 
possible for a substance in solution to affect the structure of a protoplast 
whether it enters it or does not enter it. If it enters, its effect will be deter¬ 
mined by the nature and amount of the substance, the condition of the 
protoplasm, and the natures and relative amounts of the substances in the 
protoplasmic layer and in the cell sap. It might penetrate the protoplast 
without changing it; it might alter the colloidal structure by reacting with 
the constituents of the protoplasm or merely of its surface layer; or it might 
change the electric signs of the colloids. If the substance does not enter 
the protoplast, it might react with substances in the surface layer, or by 
adsorbing ions it might change the electric signs of the colloids, and thus 
affect the colloidal structure without having entered the protoplast. It 
is apparent, then, that the terms “permeability” and “impermeability” 
are applied rather loosely to the perceptual results of several different 
processes. Physiologists have not yet been able to determine for given 
