2046 Journal of Applied Microscopy 



little of the potassium dichromate solution to flow out into the water at the 

 bottom of the test-tube. Let the thistle-tube remain in the test-tube, mark the 

 upper limit of the colored solution, and leave the preparation where it will be 

 undisturbed for several days ; each day mark the movement of the solution, cal- 

 culate the rate of diffusion. 



5. Effect of Temperature upon Imbibition. Weigh out two sets of beans or 

 peas of 30gf. each. Place one set in water maintained at 30°C., the other in 

 water at 10°-15°C. for three to five hours. At the end of that time turn off the 

 water and dry the seeds on a towel, weigh and determine the amount of water 

 absorbed in each case. 



6. Effect of Dissolved Substance upon Imbibition, (a) At the time of preparing 

 the last experiment weigh out an equal quantity of seeds and place them in a 10 

 per cent, salt solution. Keep this experiment at the temperature of one of the 

 two in the last experiment for the same length of time. Dry the seeds on a 

 towel, weigh and compare the increase in weight in the salt solution with that 

 obtained in the water. 



(/>) Instead of seeds, blocks of dry wood may be used for the same purpose. 

 Make some cubes of oak wood 2 cm. on each edge, measure them accurately in 

 the radial and tangential directions with millimeter calipers ; place one cube in 

 a 10 per cent, salt solution, one in distilled water, and one in 90 per cent, alco- 

 hol. At the end of twelve to twenty-four hours measure each block accurately 

 and determine the proportionate increase in size due to imbibition. 



7. Rise of Temperature During Imbibition. Place in a wide mouthed bottle 

 100-125 c. c. of starch which has recently been dried at a temperature of 80°- 

 40°C. Stir the starch with the bulb of a thermometer until it reaches room 

 temperature. Pour upon the starch an equal volume of water of the same tem- 

 perature as the starch, stir quickly with the thermometer and note the rise in 

 temperature within fifteen seconds after the addition of the water. If an excess 

 of water is avoided a rise of 6°C. may be obtained. 



VI. PHYSIOLOGICAL OSMOSIS. 



1. Plasmolysis. (</) Cut a small tangential section from the lower surface of 

 a leaf of Tradescantia discolor^ mount it upon a slide in a 3 per cent, aqueous 

 solution of potassium nitrate. Observe immediately with a microscope the plas- 

 molysis of the parietal layer of protoplasm, determining the limits of the vacuole 

 by the aid of the colored cell-sap. 



Observe a single cell in which the plasmolysis shows distinctly, draw off the 

 potassium nitrate with filter paper, at the same time adding water, notice the 

 increase in the size of the vacuole and the return of the protoplasm to its former 

 position. 



(/') Test gently with the finger the root of a seedling 3-6 cm. long for its 

 rigidity. Lay the seedling in a 3 per cent, solution of potassium nitrate for ten 

 minutes and test again, when it has become flaccid lay it in tap water for ten 

 minutes and note the return to turgidity. 



2. The Osmotic Strength of Cell Sap in Terms of Potassium Nitrate. Cut a 

 column 3 or 4 cm. long from a petiole or flower stalk of the calla {Richardiij) or 



