416 BOTANICAL GAZETTE [ DECEMBER 
death results without any marked withdrawal of water from the 
cell substance. 
In conclusion, it may now be safely asserted that, whereas 
there exist very many plants which suffer when removed sud- 
denly from salt water to fresh, and appear to be dependent for 
life itself on the presence of. this substance in the substratum, it 
seems certain that for Spirogyra, sodium chlorid and potassium 
nitrate act as poisons. It is my opinion, based on a considerable 
number of experiments not detailed here, that all sodium and 
potassium salts injure Spirogyra through their chemical properties 
chiefly, and exert but a minimal harmful influence through their 
osmotic properties. 
In this discussion, I have assumed the accuracy of the classic 
conclusion that the plasmolytic method as used by De Vries, 
Pfeffer, and others gives an essentially correct measure of the 
concentration of the cell sap. 
UNTVERSITY OF WISCONSIN. 
BIBLIOGRAPHY, 
. DE Vries, Hugo. Untersuchungen iiber die mechanischen Ursachen 
der Siahcckine: Leipzig, 1877. 
2. DAVENPORT, C. B. Experimental Morphology 1: 46. 1897 
3. PLATEAU, F. Recherches oo, sur les articulés aqua- 
tique. Mém. cour. l’Acad. Roy. Belgique 36 : 
4. PFEFFER, W. Pflanzenphysiologie 1 : ren [Ed. 2.] 
5. DE Vries, H. Le coefficient isotonique de la glycerine. Arch. Neerl. 
d. Sci. Exact. e. Natur 22: 384. 1888. 
6. JANSE. Plasmolytische Versuche an Algen. Bot. Centralbl. 32:21. 
7. LANDOLT und BORNSTEIN. Physikalisch-chemische Tabellen. Berlin. 
1883. 
