EXERCISE 16 

 OSMOSIS 



Materials. Several forms of apparatus may be used, choice being 

 largely a matter of convenience. The following are suggested : 



1. A "diffusion shell," as sold by supply companies, may be 

 filled with molasses or with sugar solution, stoppered with a 

 one-hole rubber stopper with glass tube inserted, and 



placed in a vessel of water. Make the stopper tight 

 by wrapping with wire or waxed cord. 



2. A piece of soaked parchment paper 

 may be tied over the large end of a thistle 

 tube which has been previously filled with 

 molasses or sugar solution. The bulb of 

 the thistle tube should then be immersed 

 in water. There is often difficulty in 

 preventing leakage due to the folds in 

 the paper. 



3. The Lyon osmometer shown in the 

 cut may be assembled, as illustrated. It 



is cheap, easily assembled, and certain in its action. See apparatus 

 list for maker. 



Directions for work. Assemble the apparatus chosen and 

 make hourly readings. 



Note that the essential features are a membrane permeable to 

 water (parchment paper), separating a dense solution (molasses) 

 from a much less dense solution (hydrant or well water). 

 What resemblances to a root can you see ? Does water tend 

 to move toward the denser or toward the less dense solution 

 in such cases as the above? Do you know whether plant sap 

 contains substances in solution ? If so, what substances are 

 known to be sometimes present ? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 79, 80. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 41, 42. 



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