ABSOEPTIOtf. 563 



greatly diffusible) are separated by a membrane or other porous substance, 

 the denser liquid becomes increased in bulk by the passage of the thinner 

 liquid into it through the membrane. This rule is indeed subject to 

 modifications, dependent upon other qualities besides density of the 

 liquids, such as their molecular relations to the substance of the separating 

 membrane, the molecular nature of the membrane itself, &c., since, of two 

 different liquids, that which is more readily imbibed by the membrane 

 passes through in a preponderating current. 



When we place simple vegetable cells with flexible cell-membranes, 

 such as many pollen-grains, yeast-globules, &c., in water, their dense 

 cell-contents absorb water and the cell-wall expands, sometimes even 

 bursts. On the other hand, placed in strong solutions of sugar or gum, 

 such cells will lose part of their contents and shrink. But these simple 

 experiments are not sufficient to indicate what takes place in the cells of 

 tissues tilled with living protoplasmic matters ; for very frequently, when 

 we place such cells in liquids differing in density from their contents, there 

 ensue successive changes of condition, which must also be involved in 

 many natural processes. Thus if we place in water a fragment of cellular 

 tissue from the region where pollen-grains are being developed in the 

 anther, or spores in sporanges, water is absorbed through the cellulose 

 coat, but the primordial utricle contracts; but when the water pene- 

 trates the latter, it swells again and sometimes expands beyond its 

 original volume, bursting the cell-membrane when this is weak. " 



The presence of a membranous or porous septum is not essential to 

 such a process of nitration and admixture as above described. Two liquids 

 of different densities placed in contact will gradually mix by the attrac- 

 tive force that the one exerts on the other. This liquid diffusion depends 

 materially in amount on the nature of the liquids colloid or crystalloid, 

 as the case may be. 



Selecting power. The recognition of endosmose as the cause of 

 the absorption of liquids by the young roots and root-hairs affords 

 some explanation of the apparently contradictory phenomena which 

 have been described by those who have experimented with a view 

 to ascertain whether plants have any selecting power. It has been 

 shown that there exist some very complex circumstances of purely 



. ! physical nature in endosmotic processes, and that simple density of 

 liquids is by no means the only important point alkaline, acid, or 

 neutral conditions of mineral salts causing special peculiarities, 

 dependent on chemical and molecular relations to the membrane or 



: porous interposed substance, and in other cases on chemical actions 

 taking place on one or the other side of the membrane. One of 

 the most interesting and suggestive experiments bearing on this 

 subject is that of Knop, who shows that the more chlorine absorbed 

 by a plant the less lime is taken up. 



Some writers assert that the roots of plants absorb all substances in- 

 differently ; and the experiments of Vogel and others appear to bear this 

 out. But, not to mention that the ashes of different plants grown in the 

 same soil have diiierent composition, Trmchinetti has shown that different 



