How Plants Draw in Various Materials 



171 



made very large and the glass tube very small, as is readily ar- 

 ranged for purposes of demonstration, the liquid will mount stead- 

 ily up before the very eyes to a height of several feet. Obviously 

 there is only one possible explanation of the rise of the liquid 

 against gravitation, viz., water must pass through the parch- 



FIQ. 56. An osmoscope, using a parchment membrane; further particulars in text. 



ment, and that not simply in a manner that is passive, but with 

 a force sufficient to overcome a considerable resistance. The same 

 result invariably follows, with a difference, however, in the rate 

 of the ascent, no matter what solution is put inside of the tube, 

 and follows, moreover, in case there is also a solution outside, if 

 only the inner solution is the stronger. This is a typical example 

 of osmosis under its simplest conditions, but it is representative of 



