1 84 



The Living Plant 



of substances in solution and in the gaseous state are so closely 

 and regularl}^ interconnected, that the same mathematical rela- 

 tions apply to them all. And as to which of the explanations is 

 correct, the future must decide. 



The reader has now a sufficiency of data for understanding 

 pretty fully the nature of osmotic absorption and pressure, which 

 we may summarize here by aid of the accompanying diagram 



(figure 63). The dissolved sub- 

 stance inside of a membrane is 

 always tending to diffuse out- 

 ward by the energy of its own 

 diffusion pressure, which de- 

 pends ultimately upon heat; 

 and if the membrane be per- 

 meable, then the substance dif- 

 fuses into and beyond it, as it 

 did from our molasses-holding 

 osmoscope; but if semiperme- 

 able then not. Meantime, 

 whether because the interrupted 



Fig 63.— Diagram to illustrate osmosis cfiffusioU-preSSUre actS fikc gaS- 

 through a permeable membrane; the ^ _ 



symbols as in figures 58, 59. In case, preSSUre tO SWcU the interior 



however, the membrane is semiperme- ,. . , , r ii • 



able the dissolved substance cannot es- UqUld, Or bCCaUSC Ot adheSlVC 



cape through it. attraction between substance 



and liquid, or because of capillary action between substance 

 and liquid, the substance draws on the water supplied by the 

 membrane, which yields it very easily so long as it can recoup 

 itself freely from the outside supply. Thus the solution swells 

 and exerts pressure until the power of the substance to with- 

 draw water from the membrane exactly balances the resistance 

 interposed to its expansion. And this is all true inside of the 

 plant or the animal as well as outside thereof, whence we may 

 now deduce another of our natural verities, to this effect, — that 

 wherever the conditions for osmotic absorption exist, the membrane 



