74 BOTANICAL GAZETTE [JANUARY 
The osmotic value of 0.16 gm. mol. NaCl in terms of atmos- 
pheres is not so readily deducible in this case as in that of cane 
sugar, and in view of the physical difficulties discussed by RENNER 
the writer has taken the corrected osmotic values given by him 
(p. 501) as a basis of calculation. By interpolation the osmotic 
pressure of 0.16 gm. mol. NaCl is about 7.2 atmospheres at room 
temperature. According to Prrerrer this corresponding value 
would be 5.7 atmospheres. 
In this concentration the cell contents became markedly dis- 
ordered after a short time, the chlorophyll band largely losing its 
spiral form. However, tests with solutions of cane sugar, slightly 
stronger osmotically, showed prompt and apparently normal plas- 
molysis. After 24 hours in this solution the chlorophyll band was 
still further disordered, although nearly all cells were clearly living 
and plasmolyzed normally in stronger concentrations. 
Osmotic value of sea water 
By the use of cane sugar solutions the osmotic pressure of 
Spirogyra here used was found to be about 6.7 atmospheres; the 
use of NaCl solutions gave about 7.2 atmospheres. Since the dif- 
ference between these values is without doubt exceeded by the 
differences in the osmotic pressures prevailing in individual cells of 
the same filament, there is perhaps little point in discussing which 
of these values shall be adopted as the basis of further calculations. 
Hence, an approximate value of 7.0 atmospheres is adopted as the 
basis of further discussion. 
The sea water used was dipped from outside the Fish Commis- 
sion pier, where it is subject to almost unceasing tidal movement, 
and gave a density reading of about 1.0210 at 71° F. This was 
diluted with distilled water in various proportions and used as a 
plasmolyzing agent for Spirogyra. A stage similar to that just 
noted as indicating beginning plasmolysis was seen in a mixture 
containing 30 paris by volume of sea water to 70 parts of distilled 
water at 22° C. In this concentration Spirogyra and Oedogonium 
agreed in showing faint indications of incipient plasmolysis. Meso- 
carpus showed more distinct traces. These traces disappeared 
inside of 24 hours. 
