1911.] 



The Permeability of the Yeast-Cell. 



307 



sulphate, comparatively small (0 - l — 0*25 as against 0*85 in the case of 

 alcohol). It seems very probable that the apparent entrance of salts is a 

 result of adsorption in the surface layers of the cell rather than absorption, or 

 it may be that the salt particles are kept back by a differential septum 

 according to the hypothesis of H. E. Armstrong (8), and that they remain in 

 the interstices of such membrane. 



The experiments with hexosephosphate are particularly interesting in this 

 connection, since this substance is present in yeast and is readily hydrolysed 

 and fermented by yeast-juice. The fact that when this substance is added 

 to yeast there is no evidence whatever of its being fermented would seem to 

 indicate that it had not been able to penetrate through to the seat of 

 fermentative activity. It thus seems highly probable that the apparent 

 ■entrance of this salt, which is well marked, is merely a surface phenomenon. 



In conclusion, the author desires to express his best thanks to 

 Dr. A. Harden, at whose instigation the work was commenced, and whose 

 kindly interest and numerous suggestions have been highly esteemed. 



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1. Nageli. 1855. ' Pflanzenphys. Unters.,' vol. 1, p. 21. 



2. Pfeffer, ~W. 1877. ' Osmotische Untersuchungen,' Leipzig. 



„ 1886. 'Unters. aus d. Bot. Inst. Tubingen,' vol. 2. p. 179. 



„ 1890. "Plasmahaut und Vakuolen," 'Abh. Math.-Phys. Kl. Sachs. 



Gesell.,' vol. 16, p. 187. 



3. De Vries, H. 1877. ' Die Mechan. Ursachen d. Zellstreckung.' 



„ 1884. " Methode zur Analyse d. Turgorkraft," ' Jahrb. f. Wiss. Bot.,' 



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 1884 A. ' Bot. Zeit.,' vol. 46, p. 229. 



1888 B. Ibid., vol. 46, p. 393. » 

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5. „ 1899. Ibid. 



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8. Armstrong, H. E. 1909. Ibid., B, vol. 81, p. 94. 



9. Harden and Young. 1908. Ibid., B, vol. 80, p. 299. 



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