* 

 80 Plant Physiology 



small thermal bottle (a tumbler may be used when double-walled 

 vessels are unavailable). Take the temperature of each powder, 

 then add 100 cc. of water at the same temperature, stir promptly 

 with a clean wooden stirring rod (the starch mixes with water 

 less readily), observe the temperatures, compare, and discuss the 

 results. 



Osmoscopc. - - Set up an osmoscope as indicated in section 

 41, using a thistle-tube and membrane, or a diffusion shell. 

 Different strengths of sugar solution, 20, 40, and 60 grams per 

 100 cc. of water, may be used to note differences in rate of flow 

 and total height of column, but no accurate quantitative results 

 are to be expected. Describe the results obtained. 



Precipitation membrane. - - Drop a crystal of copper sulfate 

 into a bottle containing 5 per cent potassium ferrocyanide, and 

 observe the formation of a semipermeable precipitation mem- 

 brane of copper ferrocyanide, and the prompt rise of an irregu- 

 lar column of solution inclosed by this, which grows and may 

 attain considerable proportions in fifteen minutes. More neatly, 

 the precipitation membrane may be studied by employing a 

 more dilute solution of potassium ferrocyanide (2 per cent) in a 

 dropper bottle into which is lowered cautiously to its position a 

 dropper tube with capillary outlet, containing a single drop of 

 strong copper sulfate. Note and describe the phenomena tak- 

 ing place. 



Plasmolysis and wilting. - - Prepare 250 cc. of .5 gram- 

 molecular (M.) solutions of potassium nitrate and of sodium 

 chlorid as stock solutions. From these solutions make dilu- 

 tions in small vials, capacity about 25 cc., to contain the fol- 

 lowing strengths of each of the above solutions, namely, .10, .20, 

 .30, and .40 molecular (M.) ; also one vial with distilled water 

 as a control. In each of the dilutions place a seedling of some 

 plant (root as nearly entire as possible) with delicate stems, or 

 leaf stalks, such as lettuce, radish, or mustard. Observe the 

 dilutions in which wilting occurs, and note the time required in 

 the solutions in which it occurs. Compare the equivalent 

 strengths of the two salts. The above experiment will illustrate 

 the withdrawal of water by strong solutions and will suggest 



