TENSION PHENOMi \A OF LIVING ELEMENTS. 121 



interpret this as showing that the anion of the salt unites with 

 an H ion of an amino group, forming a free acid, and the kation 

 of the -.dt unites with the protoplasm. It appears to me that 

 the ba-i> of this conclusion is very slight. 



Permeability may be investigated by a study of plasmolysis, 

 which consists in the shrinkage of the surface protoplasm away 

 from tin (i llulose cell wall, due to the osmotic pressure of the 

 hypertonic -olution of a dissolved substance which does not 

 I it-iit -irate. A regaining of turgor by the cell while in the hyper- 

 tonie -oliitioii indicates slow penetration of the sultance. The 

 l>la-im>l\ ii. method was originated by Xageli, who aUo noted 

 thai a shrinkage resembling plasmolysis but accompanied by 

 omuard dillu-ioii of dissolved substances, occur- at death or 

 -e\ tic injury to the cell. 1 



The plain cell is surrounded by an elastic cell \\all. The 

 internal "-m.itir pressure may be divided into three re-uliant-: 

 that aii-inu rounding up of the cell is called turgor, that re- 

 sulting in stretching of the cell wall is sometimes distinguished as 

 turgescence, and that resisting the surface ten-i.ni oi tin- cell, 

 " . ential pressure." 



The plasmolytic experiments of I Wrie^- and other-' are 

 interpreted \>\- them as indicating a select i\e impermeability 

 "I tin- pla-m.i membrane to neutral salts. 



In the plasmolytic experiments of Overtoil' all -alt- pla 

 moly/ed permanently. Non-electrolytes fell in four unmp-, 

 thus: (am -uijar, dextrose, manit, glycocoll > urea, ;_;lucenn> 

 ( -i h\ K ne -ali < 'hi>l, acetamid> methyl-alcohol, acetmiitril, ethyl- 

 alt ..hoi. phenol, aniline, isobutyl-alcohol, isoamyl-alcohol, methyl 

 acetate, eth\l acetate, butyl aldehyde, acetmie. a< etald.>\im. 

 Diffusion of substances of homologous series in< reased \\iih molec- 

 ular \\ eiiLill t . 



< >\ ei inn a-t er i. lined the permeability of plant cells to alkaloids 



1 " PtUm/rnpliy-i..!. I iitersuchungcn." 1885. 



.'. pliysikul. cVi.-wi.. iSSS. II., 415; 1889. III.. 103. 



3 (I. l.i\'int;-t>iir. " The R61e of Diffusion and Osiniir Pressure in Plant-." 

 Cliu-.ii;.'. \<j>>i; J.in-'. />')/. Ccntlb., 1887, XXXII., 21; Duggar, Trans. Acad. Sc. 

 >/. Lout-*. 1906, XVI.. 473- 



4 \'ifrlfljai.' ifr .V aturforschers. Gesell. in Zuriili, XL IV.. 88; Jahr. wiss. 

 Jit.. 1900. XXXH 



