1918] TRUE—MARINE ALGAE 77 
ing of the freezing point was —1.82° C., corresponding to an esti- 
mated osmotic value of about 22 atmospheres at o° C. (about 
23.7 atmospheres at 22° C.). Assuming the osmotic value of a 
1 per cent NaCl solution at 22° C. to be 7.6 atmospheres, in accord- 
ance with RENNER’s recalculation (p. 501), GARREY’s result would 
call for a salt content equal to about 3.1 per cent NaCl. According 
to SUMNER, OsBURN, and COLE (22), the water of Buzzard’s Bay and 
Vineyard Sound varies in salt content between 2.84 and 3.29 per 
cent total salt. 
Osmotic pressure of marine algae 
An attempt was made to determine the osmotic pressure existing 
in certain of the commoner bright green forms found abundantly 
in the neighborhood of Woods Hole. 
Cladophora gracilis var. was found growing on rocks below low 
tide level near the wall in front of the residence building of the 
United States Fish Commission. This alga grew in a position 
where the water was constantly changing and where it was not 
subject to any marked temperature variation. 
Enteromor pha intestinalis, according to Davis (6), is a type 
belonging characteristically to the region between tide levels, where 
it occurs attached to stones, shells, and woodwork. At low tide, 
therefore, it is often subject to a considerable concentration of its 
cell contents through evaporation. 
Chaetomorpha Linum, like Cladophora, is not subject to such 
wide variations, being found characteristically below the low tide 
mark. 
‘Small tufts of the filaments or pieces of the frond were placed 
in graduated series of solutions of cane sugar and NaCl and exam- 
ined with reference to their osmotic behavior. 
In the cane sugar solutions Cladophora first showed traces of 
plasmolysis in 0.85 to 0.90 gm. mol. per liter of solution, corre- 
sponding to 1.04 and 1.13 gm. mol. in 1000 gm. of water, corre- 
sponding to about 28 and 30.7 atmospheres of pressure respectively. 
Enteromor pha gave similar results in solutions containing be- 
tween 0.80 and 0.90 gm. mol. volume-normal, corresponding to 
about 0.96 and 1.13 gm. mol. weight-normal, representing 25.8 to 
