EXPERIMENTS ON OSMOSIS 37 



apparatus for some hours and note any change in the contents of the 

 tube or the heaker.i Explain. 



The rise of liquid in the tube is evidently due to water making its 

 way through the thin membrane which lines the eggshell, although 

 this membrane contains no pores visible even under the microscope. 



B. An alternative experiment is to fasten a pig's bladder or a diffusion 

 shell (obtainable of dealers in chemical and physical apparatus) to the 

 end of a glass tube six or eight feet long. For a |-inch (16-mm.) 

 diffusion shell the tube should be f-in. outside diameter; for the 

 bladder a tube must be chosen that barely enters the opening in it. 

 A tight joint is more certainly secured by using a tube a little smaller 

 than is needed to enter the opening in the shell or bladder, slipping 

 over the tube a bit of rubber tubing an inch or more long, inserting 

 this in the shell and wiring it tightly with rather fine copper wire. 

 Fasten the tube upright, with the diffusion membrane submerged in a 

 large jar of water, and pour into the open end of the tube enough 

 molasses to remain visible above the diffusion membrane. A rather 

 large tube may be filled through a slender funnel, taking pains not to 

 let the molasses stick to the sides as it descends. A narrow tube must 

 be filled before tying into the neck of the bladder, the free end of the 

 tube corked, and the other end then tied in place. Note any change of 

 level in the molasses in the tube.'* 



References. Ganong, 10 ; Detmer-Moor, 9 ; Pfeffer-Ewart, 31, I. 



EXPERIMENT XXI 



Result of placing sugar on a begonia leaf. Put a little powdered 

 sugar on the upper surface of a thick begonia leaf under a small 

 bell glass. Put another portion of sugar on a bit of paper along- 

 side the leaf. Watch for several days. Explain the results. The 

 upper surface of this leaf contains no pores, even of micro- 

 scopic size. 



STEMS 



23. The horse-chestnut or buckeye twig.* * Procure a twig of 

 horse-chestnut eighteen inches or more in length. Make a careful 

 sketch of it, trying to bring out the following points : 



A. The general character of the bark. 



1 Testing the contents of the beaker with a solution of nitrate of silver will then 

 ■show the presence of more common salt than is found in ordinary water. 



2 A still more instructive experiment is that on plasmolysis olthe Spirogyra 

 cell (Sees. 56, D, and 57, C). 



