474 



Trans. Acad. Sci. of St. Louis. 



of the algal material was then placed on a cavity slide in the 

 solution to be tested and the remainder in some of the same 

 solution in glass cylinders. The slide preparations were 

 observed for several minutes under the microscope ; and these 

 observations, as a rule, were sufficient. Nevertheless, the 

 material in the cylinders was mounted and examined after 

 from five minutes to half an hour, in order to determine if 

 plasmolysis might be delayed. The results of these experi- 

 ments are tabulated below, the concentrations (representing 

 the lowest at which any very evident plasmolysis was ob- 

 served), are given in decimals of a normal solution, which, in 

 these instances, is the same as a molecular solution. 



Table I. 



In analyzing these results it should first be stated that the 

 isotonic value of Naples sea water is calculated to be approx- 

 imately equivalent to .6 normal KNO3. Very nearly the same 

 value was also obtained for sea water by the plasmolytic test 

 with a delicate species of Spirogyra. It is to be regretted 

 that freezing point determinations were not made. 



The above table shows several points of interest. ( I ) . Bear- 

 ing in mind the isotomic relationship it is seen that the plas- 

 molyzing concentrations for NaCJl and KNO3 are relatively 

 higher, in everv case, than those for sugar. This is true 

 whether the calculation of the isotonic values is based on the 

 De Vries coefficients * or adduced from the formulae taking 



* De Vries, H. — Eine Methode zur Analyze der Turgorkraft. Jahrb. f. 

 wiss. Bot. 14:429-661. 



