322 ELEMENTS OF GENERAL SCIENCE 



324. How plants secure water. The first question is, How 

 does the water get into the roots ? In order to answer this 

 we shall have to study the peculiar behavior of solu- 

 tions. This may be shown by the use of a dense sugar 

 solution and pure water. A funnel which has been 

 filled with the sugar solution and over the large end 

 of which a piece of parchment paper has been fastened 

 is inverted in a dish of water (fig. 156). Since the 

 parchment paper is permeable to water, it might be 

 supposed that the liquid in the funnel and the water 

 outside would come to rest at the same level. This 

 does not occur excepting possibly for a very brief 

 period. The sugar solution increases hi volume, and 

 the level of the liquid in the funnel rises until it 

 overflows the top of the tube. If a longer tube were 

 attached the liquid might rise in it to a height of 

 many feet unless the pressure due to the height of 

 the column caused the paper to break. 



Careful measurements of the water out- 

 side the funnel show that it decreases in 

 volume just as much as the sugar solution 

 increases. This means that water has gone 

 through the paper into the sugar solution, 

 although the pressure due to its height 

 in the tube opposed the entrance of the 

 water. At first but a little of the sugar 



FIG. 156. A simple finds ifcs wa ? out through the paper, as 

 osmometer may be determined by tasting the outer 



A, osmometer, with solution. If there had been some sugar in 



the liquid in it stand- tne ou te r vessel of water, but a smaller pro- 

 ing at the height h ; 



B, sectional view of portion than within the funnel, we should 



osmometer, showing stiU haye nad the game kind Q f Tesu } t 

 permeable partition p 



but the more nearly the solutions on the 

 two sides of the membrane are alike in amount of dissolved 

 matter, the less will be the difference in pressure. 



