78 BOTANICAL GAZETTE [JANUARY 
30.7 atmospheres, respectively. Chaetomorpha required a 0.9 
volume-normal concentration (1.13 weight-normal), corresponding 
to 30.7 atmospheres, to produce the same effect. 
In NaC] solutions corresponding results were seen in Cladophora 
in 0.75 to 0.80 gm. mol. volume-normal. RENNER (p. 501) has 
pointed out that in NaCl the osmotic pressure is proportional to the 
molar concentration calculated on the liter of solution, o.1 gm. mol. 
having an osmotic pressure of 4.5 atmospheres at 18° C. Hence 
these concentrations correspond approximately to a range between 
33.7 and 36 atmospheres. Chaetomorpha showed first traces of 
plasmolysis in 0. 70-0 .80 gm. mol., corresponding to 31 . 5-36 atmos- 
pheres of pressure. 
The reason why an osmotically greater concentration was 
required in the case of the NaCl solution to give the same result 
as that seen in the osmotically less concentrated sugar solution is 
probably to be found in the greater facility with which these algae 
admit NaCl. It is probable that the surplus atmospheres required 
in the NaCl solution over the sugar solution roughly mark the 
greater degree of penetration of the former. The work of JANSE 
(rr) and of Drevs (8) is significant in this connection. 
In 1900 and 1901 Duccar (9) carried out similar plasmolytic 
studies on marine algae at Naples and at Woods Hole. The results 
presented in his paper seem to have been obtained at Naples, since 
the values are referred to Naples water. Experiments on Chaeto- 
morpha Linum made with solutions of osmotic agents in distilled 
water, as would be expected, showed markedly higher osmotic pres- 
sures than the writer found at Woods Hole. At Naples Chaeto- 
mor pha was found to be isosmotic with 1.26 gm. mol. by volume 
cane sugar or 1.73 gm. mol. by weight, having an osmotic pressure 
of about 34.7 atmospheres; with 0.93 gm. mol. of NaCl by volume 
equal to about 41.8 atmospheres; and with 1.40 gm. mol. by 
volume of KNO,. The freezing point of Mediterranean water was 
found by Borrazzi (4) to be A= —2.29 C. , Corresponding to about 
27.6 atmospheres at o° C., or about 30 atentienhiees at 22°C, This 
is the equivalent of iene 1 per cent NaCl, or 6.2 atmospheres 
higher than values obtained at Woods Hole by GARREY. Analyses 
of Mediterranean water from Naples reported by Roru (21) gave 
