1918] TRUE—MARINE ALGAE 3 
an undoubted “‘starting”’ of the protoplast from the wall seen. 
This appeared inside of 20 minutes and still persisted at the end of 
an hour, but was scarcely noticeable after 20 hours. The osmotic 
pressure of the cell contents of these algae was, therefore, very 
nearly equal to 0.25 gm. mol. of cane sugar in a liter of solution. 
In calculating this value in terms of atmospheres, the values of 
Morse and Frazer (15) were used. However, since Morsr’s 
osmotic determinations were made on the basis of gram molecules 
dissolved in 1000 gm. of water, this value was reduced to the latter 
basis by means of RENNER’s formula: li aha , m being the given 
1000-214 ” 
number of gram molecules in 1000 ccm. of solution. The osmotic 
equivalent of the algae in question became, therefore, 0.264 gm. 
mol. in 1000 gm. water. The osmotic values of a series of cane sugar 
solutions determined in atmospheres by Morse (16) and associates 
were plotted in a series of curves on which by interpolation the 
osmotic value of 0.264 gm. mol. weight-normal at 22° C. (the tem- 
perature at which the plasmolyzing solutions stood at the time of 
the determination) was found to be about 6.7 atmospheres. 
According to PFEFFER the corresponding value would be about 
5-9 atmospheres. 
Tests on Spirogyra showed that the cell contents were osmoti- 
cally equal to a solution of NaCl containing about o. 16 gm. mol. in 
a liter of solution. In solutions of NaCl of this degree of dilution 
the difference between volume-normal and weight-normal is negli- 
gible in view of the wide range of error in the biological data. This 
may be seen by calculating weight-normality in accordance with 
the following formula given by RENNER (p. 500). When M equals 
the molecular weight of NaCl (58.5), m equals the number of gm. 
mol. per liter of solution, and s the specific gravity of the given solu- 
tion, the corresponding weight-normality equals SPECIE 
The specific gravity (20° /4° C.) of a 0.16 volume-normal NaCl 
(0.93 per cent) solution obtained by interpolation on a curve 
based on LANDoLT-BORNSTEIN-RotH (13, p. 260) is about 1.005. 
Solving the equation, the corresponding value weight-normal is 
0.1607 gm. mol. in 1000 gm. water. 
