TABLES TO DETERMINE OSMOTIC PRESSURE 
419 
quite sufficient for biological work. Since then, however, Mr. John 
V. Lawrence and I in determinations of freezing point depressions on 
the juices of the plants of the southwestern deserts about Tucson and 
of the Jamaican coastal deserts have repeatedly found values far beyond 
the range of the table there published.^ 
It has seemed worth while therefore to extend the tables to 6°. 
In using such a table one must of course remember the difficulties 
which surround the problem of the osmotic pressures of concentrated 
solutions — ^even those of pure solutes in pure solvents under the 
controlled conditions of the physico-chemical laboratory. But the 
physiologist cannot neglect the many problems presented by the 
concentration of vegetable saps until physical chemisrs are in full 
agreement concerning all details. Quite to the contrary he must use 
the best methods he can under the pecuHarly complex and difficult 
conditions which surround his work and express' his results in 
consistent terms, remembering that methods and formulae which 
are the best that are practicable at present may soon have to be 
replaced by others. 
Station for Experimental Evolution, 
Cold Spring Harbor, Long Island, N. Y. 
1 These results confirm those obtained in cryoscopic studies by Cavara and by 
plasmolytic methods by Fitting, in that they show that very high concentrations 
may occur in plants growing in their natural habitats.* As yet we have not found 
concentrations quite so high as some they report. 
