476 Trans. Acad. Sci. of St. Louis. 



computation cannot be made so accurately, since the isotonic 

 value of sen water in terms of sugar was not experimentally 

 determined with Spirogyra. This value is probably close to 

 9 N cane sugar, and with this relative value a provisional 

 computation may be readily adduced from the table. Under 

 any circumstances, the results are unique in that the com- 

 puted strengths of the pure sugar solution required are nearly 

 25 to 50 per cent too high, that is, the concentrations giving 

 plasmolysis experimentally are low. We have, therefore, for 

 each of the four algae a comparable series of these three solu- 

 tions, in which the plasmolyzing concentrations differ consid- 

 erably between sugar, the one extreme, and KNO3 the other. 



Attention should be called to the fact that the figures for 

 KNO3 given in the above table, are not in close agreement 

 with the results of Janse,* who found that a solution of .14 

 N potassium nitrate is osmotically equivalent to the cell sap 

 of Chaetomorpha aerea. He gives, however, very brief re- 

 sults ; and aside from having employed a different species of 

 alga, his methods of treating the algae, as well as an allow- 

 ance for the personal equation in determing what is the first 

 evidence of plasmolysis, may be suflScient to account for the 

 disagreement. t Some of the marine algae quickly accomodate 

 them-elves to plasmolyzing strengths, or readily recover from 

 the plasmolytic effects, doubtless due to the penetration of 

 the solute. This did not, however, enter as a special factor 

 which would account for the difference in the results, as my 

 observations were made from the momentof immersion of the 

 algae, and these furnish the higher values. 



There is considerable variation in the turgor between cells 

 in different filaments, even between cells in the same fila- 

 ments, and such irregularities were also noted by Janse. In 



♦ Janse, J. M. PlaMHolytische Versuche an Algen. Bot. Centrbl. 82 : 21- 

 26. 1887. 



t In dlscnssing these results with Mr. H. S. Reed, he brought to my at- 

 tentioQ a considerable series of unpublished osmotic determinations which 

 he made at the Woods Holt? Marine Biolog. Lab. in th« summer of 1901. He 

 employed six marine aluae ami a. variety of salts, the solutions being made 

 only in distilled water. His results, as shown by the table appended, 

 are iateiestinu, and while .showing considerable variation with different 

 algae, the averajjes are especially instructive. With his consent I give 



