82 



Plant Physiology 



of the alga, observing under the microscope for ten minutes 

 whether there is or is not some plasmolysis. Then, according 



to the result, prepare dilutions of 

 less or greater concentration, and 

 determine accurately the thresh- 

 old of plasmolysis. For accurate 

 work the hanging-drop culture 

 may be employed. Determine 

 the osmotic strength also in terms 

 of cane-sugar. Peel off some of 

 the lower epidermis (with colored 

 cell-sap) of Cyclamen or Trades- 

 cantia zebrina, or use leaf hairs of 

 a cucurbit, and determine the os- 

 motic strength of these cells. 



With cells of any plant just 

 distinctly plasmolyzed determine 

 if turgor may be restored by 

 irrigation with tap or distilled 

 water. 



Shrinkage. With any of the 

 above plant material mounted in 

 water measure accurately with 

 the ocular micrometer a cell easily 

 located. Draw off the water and add successively stronger 

 salt solutions until approaching the point of plasmolysis ; re- 

 measure ; plasmolyze the cell, and again measure. Compare 

 the results with respect to shrinkage. 



Protoplasmic permeability. Into a solution of methylene 

 blue, 1 part to 100,000 parts of water, place a seedling of radish 

 or mustard with well-developed root-hairs ; also filaments of 

 Spirogyra and a sprig of Elodea. In two hours examine the 

 root-hairs, the cells of Spirogyra, and the leaf cells of the Elodea 

 for penetration of the dye, and discuss the results. 



Sap or root pressure. Utilizing suitable plants in the open, 

 or potted specimens, determine the amount of water exuded 

 upon decapitation, and also the pressure of exudation in two 



FIG. 22. Simple method of 

 demonstrating exudation 

 from a decapitated plant. 



