PLANT PHYSIOLOGY. 



(If tJie mustard roots are placed in strong solution of potash, they 

 iv 'ill show the ducts and growing p tint without sectioning ; the proto- 

 plasm in t/ie Jiairs may be made more plain by plasmolysis with a 

 weak (5$) solution of salt ; tJie important transverse distribution of 

 ducts and sieve elements can be seen only in cross-sections.} 



Your studies of the structure of the roots (under 18) show 

 that the special water-absorbing parts of plants, i.e., the hairs 

 on the roots, are not open tubes, but closed sacs. Water must 

 therefore enter through imperforate membranes, and hence it 

 is necessary to consider first the physics of the transfer of 

 liquids through membranes, i.e., the physical process of 

 Osmosis, involving Diffusion. 



19. What is the nature of Diffusion? 



Answer by Experiment 5. 



EXPERIMENT 5. Fill with water an erect test-tube, or equivalent, 

 placed where it cannot be jarred, Drop quickly to the bottom a 

 piece of solid fuchsin, and observe the diffusion of the color. Form 

 a consistent mental picture of the direction of action and character 

 of the energy involved, and indicate these in a diagram.* 



(Keep under as constant temperature as possible, so that tJie diffu- 

 sion may not be too mucJi influenced by convection currents^) 



20. What is the nature of diffusion through a membrane, i.e., 

 of Osmosis? 



Answer by aid of Experiment 6. 



EXPERIMENT 6. For the study of this subject it is needful to use 

 a membrane capable of being wetted by two liquids placed on oppo- 

 site sides of it, and one at least of which must contain some crystal- 

 lizable substance in solution ; arrangements should be made, also, to 

 measure any quantitative differences in the passage of the liquids 

 through the membrane. Construct an osmometer as follows (see 

 Fig. 10): Over the lower end of a burette, or other calibrated tube, 

 1 6 mm. in diameter, slip the end of a soaked diffusion-shell of 

 1 6 mm. diameter, and tie tightly with waxed thread. Fill cup and 

 burette to the zero-mark with molasses (i.e., a colored solution of 

 sugar) and immerse them to the zero-mane in a large dish of pure 

 water. Cover both liquids with a film of oil, and add to both 

 enough formaline to make a 2% solution. Observe and record fre- 

 quently ; calculate and express in a curve the quantitative changes 



* On this consult earlier, page 19. 



