416 Martin : Effect of concentrated solutions 



produce plasmolysis. When these isotonic concentrations were 

 determined, specimens were placed in the required concentration 

 of glycerine, urea, or acetamid, and left until turgidity was restored. 

 They were then tested with potassium nitrate to determine the 

 concentration necessary to replasmolyze them. The exact method 

 of experiment differed according to the material used, and may 

 best be described under each material. 



In order that more accurate results might be obtained, normal 

 solutions of the substances used were made. The solutions were 

 made up on the basis of taking the number of grams represented 

 by the molecular weight of the solute, dissolved in a htlle distilled 

 water, and this solution diluted to one litre. A normal solution is 

 designated by /i, a one half normal by ///2, etc. 



Philotria 



The presence of numerous chloroplasts, as well as the more 

 or less rectangular appearance of the cells in optical section, show 

 incipient plasmolysis readily. The plants used had been in jars of 

 water in the greenhouse for about two months. Fresh sprigs 

 from these were kept in a glass of water, which was frequently 

 changed, on a table near a south window. The importance of 

 having good fresh material cannot be overestimated. 



In experimenting with Philotria, whole leaves were broken 

 from the stem with a small pair of forceps. This usually injured 

 some of the basal cells, which were therefore not considered in 

 determining the necessary concentration for plasmolysis. 



The surplus water was removed from the leaf before applying 

 theplasmolyzing solutions, in order to preserve the concentration 

 of the solution used. Care was taken, however, not to remove too 

 much water, lest the leaf should become flaccid, and vitiate the 

 results. The leaf was mounted in a drop or two of the plasmolyz- 

 ing solution, under a cover-glass. This solution was drawn off 

 once or twice by filter-paper, and fresh solution added, both to 



keep the concentration correct and to bring about more rapid dif- 

 fusion. 



Potassium nitrate. Isotonic concmtratioiL — As a result of sev- 

 eral general tests, it was found that ;//4 potassium nitrate would 

 just produce plasmolysis in leaves of Philotria. This concentration 



