62 DIFFUSION AND OSMOTIC PRESSURE 



nal condition if left in the plasmolyzing solution. This 

 author also observed that the presence of an acid or base, or 

 of any other poisonous substance, made the protoplasm 

 rapidly permeable to such salts as KNO 3 and NaCl. The 

 cells of the epidermis of leaves of Tradeacantia, Curcuma, 

 and Begonia rex appeared to be impermeable to KNO 3 . 

 The same author 1 found the protoplasm of beets to be per- 

 meable to NaCl. Janse 2 found a similar return of tur- 

 gidity in the case of marine algae (e. g., Chaetomorpha) 

 which were allowed to remain in a solution of KNO 3 or of 

 NaCl which plasmolyzed them at first. He also found that 

 the protoplasts of these algae are permeable to cane sugar. 

 When plasmolysis was brought about in a solution of this 

 substance, turgor gradually returned, but this process took 

 about four times as long here as in a KNO 3 solution. In 

 Spirogyra the same general facts were observed, but the 

 permeability is not as marked here as in the marine forms. 

 In summing up the results of his second paper, this author 

 states that he has found the protoplasm of the following five 

 plants permeable as follows : 



Cheetomorpha is permeable to KNO 3 , NaCl, cane sugar. 

 Spirogyra is permeable to KNO>, NaCl, grape sugar. 

 Tradescantia and Curcuma are permeable to KNO 3 , NaCl. 

 Stratiotes is permeable to KNO 3 . 



Glycerin and urea have been shown by De Vries 3 and 

 Klebs 4 to penetrate nearly all plant cells with great readi- 



i H. DE VRIES, " Sur la permeabilit6 du protoplasma des betteraves rouges," 

 Arch, uteri., Vol. VI (1871), pp. 117-26. 



2J. M. JANSE, " Plasmolytische Versuche an Algen," Bot. Centralbl., Vol. XXXII 

 (1887), pp. 21-6; IDEM, "Die Permeabilitat des Protoplasma, 1 ' Verslag. en Mededeel. 

 d. k. Akad. v. Wetensch. te Amsterdam, 3 Reihe, Vol. IV (1888), p. 332. 



3H. DE VRIES, "Ueber den isotonischen Coefficient des Glycerins," Bot. Zeitg., 

 Vol. XLVI (1888), pp. 229 ff. ; IDEM, " Ueber die Permeabilitat der Protoplaste fur 

 Harnstoff," ibid., Vol. XL VII (1889), pp. 309 ff. 



*G. KLEBS, "Beitrage zur Physiologie der Pflanzenzelle," Unters. aus d. hot. 

 Inst. zu Tubingen, Vol. II (1888), pp. 489 ff. ; IDEM, " Beitrage zur Physiologie der 

 Pflanzenzelle," Ber. d. deutsch. hot. Ges., Vol. V (1887), pp. 181-9. 



