54 DIFFUSION AND OSMOTIC PRESSURE 



same manner. In consideration of such facts as these much 

 stability cannot be predicated of these membranes, and thus, 

 in a discussion of the osmotic properties of the cell, it will 

 probably be safer to regard the intra-vacuolar pressure as 

 arising from the semi-permeability of the lining layer of 

 protoplasm as a whole. 



In a vacuolated cell the osmotic pressure sometimes 

 becomes so great ^as to burst the cellulose membrane. This 

 is notably so in the bursting of the asci in certain ascomy- 

 cetous fungi and in the explosion of the hypo-sporangial 

 region in Pilobolus. Many plant cells may be made to burst 

 in this way by immersing them in a very weak solution or 

 in distilled water. For example, Lidforss 1 found that the 

 pollen grains of many plants (notably the Liliaceae, as 

 Funkia, Asphodelus, Anthericum, etc.) exploded in this way 

 when put into water. Noll 2 has shown that when certain 

 marine Siphoneae are placed in pure water their filaments 

 are apt to burst. Also Curtis 3 noted that when the common 

 molds were placed in water after having been accustomed 

 to a concentrated solution, the hyphal tips often burst in the 

 same manner. Similar observations were made among ani- 

 mals by Gogorza, 4 who records the bursting of blood cor- 

 puscles in certain marine forms when they were killed by 

 being placed in fresh water. 



II. PLASMOLYSIS 



When a plant cell is surrounded by a solution of greater 

 concentration than that contained within its vacuole, the 

 phenomenon of plasmolysis occurs. The greater osmotic 



1 B. LIDFORSS, " Zur Biologie des Pollens," Jahrb. f. wiss. Bot., Vol. XXIX (18%), 

 pp. 1-138. 



2 F. NOLL, " Beitrag ?.ur Kenntniss der physikalischen Vorgange welche den 

 Reizkrftmungen zu Grunde liegen," Arb. d. bot. Inst. in Wilrzburg, Vol. Ill (1888), 

 p. 496. 



30. CURTIS, "Turgidity inMycelia," Bull. Torr. Bot. Club, Vol. XXVII (1900), 

 pp. 1-13. 



4 GOGORZA Y GONZALEZ, " Influencia del aqua dulce en los animales marines," 

 Annalesde la soc. espagn. hist, nat., Vol. XX (1891), pp. 220-71. 



