SOLUTION AND FIXATION OF BIOCOLLOIDS 137 



these facts has come from Stiles and Jorgensen, 6 and a fuller 

 estimate of their importance must precede any further profitable 

 discussion of the hydration and water-relations of living matter. 



It is to be noted that plasmolysis or decrease in the volume of 

 the protoplast occurs in the immersions and during the extrac- 

 tion of acids from cell-masses, and that it also takes place in 

 wilting. The plasmolytic contraction from the walls may be 

 held in such manner as to be irreversible and the protoplast thus 

 modified may continue to live. Death is therefore not identical 

 with irreversible plasmolysis. 



Plasmolysis by osmotic action is accompanied by losses and 

 by penetrations and perfusions of complex character in the 

 many phases of the cell colloids. Plasmolysis in wilting is in 

 some respects a simpler matter. Vaporization of water from 

 the cell-walls is followed by replacement movements from the 

 cell colloids, which result first in a lessened volume of the proto- 

 plast and finally in the progressive concentration of all sub- 

 stances, especially those dissolved in the vacuoles, and in the 

 more liquid phases of the colloids. The fact that the acids may 

 be readily extracted in greater proportion from dried specimens 

 than from fresh tissues suggests that these substances may have 

 crystallized out to some extent after the manner of amino-acids 

 incorporated in colloidal mixtures. The same may be true to 

 some extent of the salts. There is also much in favor of the 

 conclusion that changes take place in the colloidal mesh, as a 

 result of a loss of water, and of the action of adsorbed bases which 

 cause coagulations not reversible by simple hydration. Aggre- 

 gations which may effect the imbibition capacity of or water- 

 relations of masses of protoplasm, especially its external layers 

 or phase boundaries even in the most highly hydrated condition 

 also may occur. 



6 Stiles and Jorgensen. I. Studies in Permeability. Ann. of Bot. 29: 349. 

 1915. 



The swelling of plant tissue in water and its relation to temperature and 

 various dissolved substances. Ann. of Bot. 31: July and October, 1917. 



