ABSORPTION FROM THE SOIL BY PLANTS 235 



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. 116). 

 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 

 in 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 outside 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. (How 

 much pressure per square inch on the inside per foot 

 of height ?) A very little of the sugar finds 

 its way out through the paper, as may be 

 determined by tasting the outer, solution. 

 If there had been some sugar in the outer 

 vessel of water, but a smaller proportion 

 than within the funnel, we should still have 

 had the same kind of result, but the more FIG. 116. A simple 

 nearly the solutions are alike in amount osmometer 



of dissolved matter, the less will be the A > osmometer, with 



, . ., . the liquid in it stand- 



difference in pressure. ing a t the height h; 



It will be seen that the essential things B > sectional view of 



. . . osmometer, showing 



about Our experiment are two solutions permeable partition p 



separated by a semi-permeable partition. 



It is also clear that the water passes through the partition and 



dilutes the denser solution, thus increasing its volume. The 



