80 BOTANICAL GAZETTE [JANUARY 
should be borne in mind in comparing the results of different 
observers. It seems from the observations of SUMNER (22, p. 53) 
and his associates that the salt content at Woods Hole is known to 
vary between 2.84 and 3.29 per cent total salts. 
The osmotic surplus found in the algae studied is easily calcu- 
lated by subtracting 22.6 atmospheres from the observed osmotic 
pressures. The results of such a calculation appear in table III. 
TABLE II 
OSMOTIC SURPLUS IN MARINE ALGAE AT Woops HOLE 
OSMOTIC SURPLUS DETERMINED WITH 
ALGAE 
: Cane sugar Sodium chloride 
Cladophora gracilis Js.4 atmospheres | {11.1 atmospheres 
626 5e Oe OP ee ee ae 66 Fee \8 : t \13 : 4 
Enteromorpha intestinalis............... ao Reg aa Rea Oe SEY 
Chaetomorpiia Linunt: 0.2 ci ee: 8. 8.9 
iz : (13.4 
PTCCIOE VONER in io i ei ces 6.6 atmospheres} 11.7 atmospheres 
The strikingly higher values obtained with NaCl are probably 
due to the penetration of this substance with the consequently 
higher concentration required to produce traces of plasmolysis. 
The writer, therefore, is inclined to regard the lower reading 
obtained with cane sugar as more nearly the true value in this case. 
It should be borne in mind, however, as COPELAND (5) has shown, 
that this osmotic surplus is subject to influence from external con- 
ditions through their effect on nutrition and in other ways. 
Summary 
1. By means of the plasmolytic method it is shown that the 
osmotic pressure in the cells of Spirogyra, Zygnema, and Oedogonium 
found in Nobska Pond, near Woods Hole, Massachusetts, at 22° C., 
is equal (1) to about 0.25 gm. mol. in a liter of solution of cane 
sugar, corresponding to 6.7 atmospheres, (2) to about 0.16 gm. 
mol. NaCl per liter of solution, corresponding to 7.2 atmospheres, 
and to a 30 per cent sea water solution (sea water = 2.93 per cent 
total salts). 
