PASSAGE OF WATER FROM PLANT CELL. I I 3 



in great flakes. The molecules of water force their way between 

 the lack and the paper and literally pry the two apart. 



Water imbibed from solutions usuall}' leaves the solute behind 

 and penetrates the substance in an almost pure state. The water 

 contained in the cell wall especially is probably nearly pure. The 

 purity is somewhat proportional to the force required to penetrate 

 the substance. 



Xot only will an imbibing' substance, if homogeneous or nearly 

 so throughout, contain water in the interstices between the par- 

 ticles of which it is composed, but also the same forces acting will 

 cause molecules of water to become attached to the surface par- 

 ticles as well, thus fc^rming a layer of water over the whole surface 

 of the substance. The above experiment with lack and paper con- 

 stitutes a very pretty demonstration of the presence of such a laver, 

 as does also the fact that the surface of an imbibing body reacts 

 toward oils and resins in the same way as does the surface of free 

 water. Oils and resins will not adhere to the surface of a soaked 

 body of this sort. Such a layer of water then covers the surface 

 of both cell wall and protoplasm, but that upon the outer surface 

 of the protoplasm and the one on the inner face of the cell wall, 

 when these two structures are in contact, necessarily fuse into one. 

 Since the molecular force in a given substance is constant, it fol- 

 lows that the thickness of the water film will depend upon the 

 quantity of water at command. In general, the more water pres- 

 ent the thicker will be the layer and the less firmh- will it be held 

 by the substance, since some of the particles are necessarilv at a 

 distance from those of the substance attracting them. 



The plant cell then is essentially a system composed of the fol- 

 lowing parts : A film of nearly pure water of varying thickness 

 bordering on the intercellular space ; a cell wall filled with water 

 of imbibition, which is continuous with the water of imbibition in 

 the protoplasm ; and a cell sap which is continuous with the water 

 in the protoplasm. Normally the whole system forms a complex 

 in a state of equilibrium.* If water is taken from one member of 

 the series a readjustment will follow throughout the whole. 



* See also Miiller-Thurgau. Ueber das Gefrieren und Erfrieren der 

 Pflanzen. Landw. Jahrb. 9: 1880, see page 144 and 145. 



