74 DIFFUSION AND OSMOTIC PRESSURE 



At different times and under different conditions the 

 permeability of certain protoplasts apparently changes 

 greatly. The presence of poisons may cause the protoplasm 

 to become more permeable to other substances. Thus, 

 Maquenne 1 found that HgCl 2 caused a marked increase in 

 the permeability of the protoplasm of the cells of Helianthus 

 seedlings to plasmolyzing agents. Similarly DeVries 2 found 

 that plasmatic membranes which were normally impermeable 

 to KNO 3 and NaCl could often be made permeable to them 

 by treatment with an acid or a base. With animal muscle 

 Loeb 3 has shown that acids, bases, and other chemicals exert 

 a great influence upon the water- absorbing power of the 

 cells. This may be due to changes in permeability. 



Partial or complete plasmolysis may act in the same way. 

 Oltmanns * was able to cause Fucus cells to give out coloring 

 matter by placing the tissues in concentrated solutions. 

 Both of these reactions must consist in an alteration of the 

 physical (perhaps chemical) structure of the protoplasm. 

 On the other hand, an increase in turgor above the normal 

 may cause the same change. This seems to be the case in 

 the guttation from the water pores of the leaves of the 

 tomato, balsam, etc. When the turgor pressure in the 

 cells bordering these water pores passes a certain limit, the 

 protoplasm apparently becomes altered so that the cell sap 

 oozes out and appears in droplets on the leaf-tips where 

 water pores are present. Czapek 5 describes a similar phe- 



i L. MAQUENNE, " Sur la pression osmotique dans les graines germees," Compt. 

 rend., Vol. CXXIII (1896), pp. 898, 899. 



2H. DE VEIES, " Plasmolytische Studienft. d. Wand d. Vacuolen," Jahrb.f. wiss. 

 BoL, Vol. XVI (1885), pp. 465-598. 



3J. LOEB, " Physiologische Untersuchungen fiber lonenwirkung " : I. Mitthei- 

 lung, " Versucheam Muskel," Pflilgers Arch.f. d. ges. PhysioL, Vol. LXIX (1897), pp. 

 1-27. 



*F. OLTMANNS, "Ueber die Bedeutung der Concentrationsanderung des 

 Meerwassers fur das Leben der Algen," Sitzungsber. d. k. preitss. Akad. d. Wiss. zu 

 Berlin, Vol. X (1891), p. 183. 



5 F. CZAPEK, " Zur Lehre von den Wurzelausscheidungen," Jahrb. /. wiss. Bot., 

 Vol. XXIX (1896), pp. 321-90. 



