172 



The Living Plant 



all conditions, inside of plants and animals, as well as outside of 

 them. It thus constitutes one of the great natural verities which 

 may be stated as follows; — when water and a solution, or two solu- 

 tions of different strengths, are separated by a suitable membrane, 



there is always a forcible osmotic 

 movement of liquid through the mem- 

 brane from the weaker to the stronger 

 solution. This is one of those ele- 

 mental cosmical facts which the 

 reader should fix in his mind as one 

 of the pillars of his natural knowl- 

 edge. 



If, at this point, it seems to the 

 reader that however interesting such 

 experiments with parchment and 

 tubes may be, they can have little 

 to do with the processes inside of a 

 living plant, let him take a leafy 

 potted Begonia, Fuchsia, or Mar- 

 guerite, cut everything away close 

 down to the roots, and connect the 

 stump with a plain glass tube like 

 that which was used in the foregoing 

 experiment. Then, I believe, he will 

 change his opinion, for water always 

 rises in the tube, though slowly, to 

 a height of two or three feet (figure 

 57). There are of course plenty of 

 differences in detail, but sugar-holding cup and live roots agree in 

 the central and crucial feature that they absorb water into a sugar 

 solution through imperforate membranes and force it up tubes 

 against gravitation. There is no question that the primary 

 forces are the same in both cases, and that the absorption of 

 water by roots is osmotic. 



Fig. 57. — An arrangement in which 

 the parchment cup of figure 56 is 

 replaced by living roots. 



