90 



APPLIED BIOLOGY 



molasses up the tube for several days. Change the water when it 

 becomes discolored by exuded molasses. If the shell does not 

 break, or leak at the cork, the column of fluid may rise to a height 

 of 8 or 10 feet. The glass tube may be made 

 longer by joining on other tubes with pieces of 

 rubber tubing for the joints. 



Or a piece of gold-beater's membrane, or of 

 fish-bladder, may be tied over the funnel of a 

 thistle-tube, or even on one end of an ordinary 

 tube, filled with molasses in the same way and 

 placed in water. 



The above experiment shows that sugar 

 solution (molasses) " attracts " water 

 through a membrane so strongly that the 

 pressure developed will raise a column of 

 water many feet in height. Like roots, 

 as stated above, the membrane used for 

 the experiment has no visible pores. The 

 water must pass through spaces which are 

 far too small to be seen with the aid of 

 the strongest microscope. Such diffusion 

 or absorption of water through a mem- 

 brane without visible pores is called 

 osmosis (sometimes osmose) in the science 

 of physics. The- verb to osmose will be 

 used in this book. For an explanation of 

 osmosis one must study the advanced 



FIG. 36. Diagram of 

 apparatus for os- 

 mosis, t, glass 

 tumbler; m, mem- 

 brane bag; w, level 

 of water in tumbler; 

 s, sugar-solution in 

 bag and up to level 

 x\ c, cork tied into 

 mouth of the bag; 

 g, glass tube of ^ 

 inch bore fitted into 

 hole in cork. Rise 

 of fluid higher than 



x indicates osmosis books on physics : but for the purposes 



of water into the , . ,.,... u 



sugar solution faster of plant study it is sufficient to remember 

 than that of the the above experiment showing osmosis 

 iato'the wa?en through a membrane which has no visible 



pores. 



Another point needed for our later studies is that water 

 having substances in solution may osmose. For example, 

 in the above experiment the water became discolored by 

 the exuded molasses (solution of sugar in water), proving 



