76 DIFFUSION AND OSMOTIC PRESSURE 



out a striking parallelism in the behavior of plant nuclei 

 which have been either frozen, dried, or subjected to the 

 osmotic action of a concentrated solution. In all these cases 

 water was found to be extruded from the nucleus. The 

 nuclear material took on a peculiar appearance not unlike 

 that of karyokinetic figures. 



Krabbe 1 experimented upon the effect of rise in tempera- 

 ture upon the absorption of water by various plant cells, 

 finding that the rate of absorption rises with the tempera- 

 ture. This author supposes the response to be due to a 

 physical change in the protoplasm, caused by the higher 

 temperature. 



But the best series of experiments on the change in pro- 

 toplasmic permeability due to temperature variations is that 

 of van Rysselberghe. 2 He worked with a variety of plant 

 cells (Sambucus, Tradescantia, Begonia, Lemna, green alga3, 

 etc.) and found that Krabbe's general result is true. The ratio 

 of increase in permeability to water becomes less, however, as 

 the temperature rises. From C. to 5 C., this ratio is 0.05 ; 

 from 5 C. to 18 C., 0.043 ; and above the last-named tempera- 

 ture, 0.1. The ratios between the permeability to water at 

 and that at 6, 12, 16, 20, 25, 30 



are: 1, 2, 4.5, 6, 7, 7.5, 8. 



The total amount of water absorbed by a cell is not changed 

 by variations in temperature; the rate of absorption alone is 

 affected. The nature of the protoplasm does not appear to 

 have any effect on the total amount of water absorbed or 

 given out by a cell ; this is determined by the osmotic pres- 

 sure of the sap and by the temperature. Permeability to 



!G. KRABBE, "Ueber d. Einfluss d. Temperatur auf d. osmotische Processe 

 lebender Zellen," Jahrb.f. wiss. Bot., Vol. XXIX (1896), pp. 441-98. 



2F. VAN RYSSELBERGHE, "Influence de la temperature sur la permeabilite du 

 protoplasme vivant pour 1'eau et les substances dissoutes," Recueil de Vinst. hot. de 

 Bruxelles, Vol. V (1901), pp. 209-49; IDEM, " Reaction osmotique des cellules veg6tales 

 a la concentration du milieu," Mem. cour. pub. par Vacad. roy. de Belg., Vol. LVIII 



), pp. 1-101. 



