AGRICULTURAL BOTANY 



125 



of the root hairs. This process of absorption is called 

 osmosis. 



Suggestive Experiment. Dissolve in water all the sugar 

 that the water will hold ; that is, make a saturated solution of sugar and 

 water. Invert a small glass funnel or a thistle tube over the larger end 

 of which a bladder or other animal membrane has been tightly tied, and 

 pour in some of the sugar solution. Lower 

 the funnel or tube into a glass of water 

 until the water in the glass and the solution 

 in the funnel are at the same height. Let 

 this stand for a few hours. It will then 

 , be observed that the solution has increased 

 in volume, that is, has risen in the tube. 

 The water in the glass must have passed 

 through the membrane and diluted the 

 sugar solution. This passage has taken 

 place notwithstanding the fact that there 

 are no pores in the membrane which the 

 highest power microscope can reveal. 

 This passage of a liquid through an animal 

 or vegetable membrane is called osmosis. 



General Laws of Osmosis. 



First Law. Two liquids separated 

 by a membrane will mix, and 

 the more rapid flow will be 

 toward the liquid having the more 

 dense solution. That is, if water 

 containing solids in solution is 

 separated from pure water by a 

 membrane, the greater flow will be through the mem- 

 brane from the pure water into the solution. 



Second Law. Substances that crystallize readily 

 and are easily dissolved, such as salt and sugar, pass 



FIG. 52. Experiment 'llus- 

 trating Osmosis. 



