OSMOSIS 



67 



through the bladder as rapidly as the water outside can 

 pass in. Then there is evidently absorption of water and 

 pressure in N which forces the liquid higher than in 

 the bottle. The liquid in N continues to stand higher 

 than in the bottle while this absorption goes on. 



140. The cell-sap of the root-hair absorbs water from the 

 soil bij osmotic action. The above experiment enables 

 us to understand how the countless 

 little root -hairs act, each one like 

 the tube X, if only the whole surface 

 of the tube were a bladder membrane, 

 or something acting similarly. The 

 soil water does not contain much of 

 the land's fertility : that is, it is a 

 very weak solution. The active little 

 root-hair, on the other hand, is always 

 filled with cell-sap, a more concen- 

 trated solution : hence soil water must 

 come in, and along with it come also 

 small quantities of dissolved food n 

 materials. Some of these materials 

 may be fertilizers which have been 

 applied to the land. 



141. The plant absorbs these solu- 

 tions as long as they are used for 

 the growth of the plant. The salts 

 which are dissolved in the soil water 

 also diffuse themselves through tin 

 root-hairs, each ingredient tending independently to be- 

 come as abundant inside the root-hair as outside in the 

 .soil water. Once inside the root-hair, these absorbed 



solutions pass on to rout and stein and leaf, to be 



utilized in growth. As Long ;is they nre used, how- 

 ever, nmre must come into the root-hairs, in order to 

 restore the equilibrium. Thus thus, substances which art 



A: 



IOC. To Illustrate osmosis. 

 membrane of the 



