RECENT ADVANCES IN SCIENCE 579 



that it is impossible to estimate permeability by a comparison 

 of isotonic coefficients as determined physico-chemically and 

 by plasmolysis. 



A method allied to the plasmolytic method has been 

 adopted by Brooks (Amer. Journ. Bot. 3, 562-70, 1916) for 

 observations on permeability. When scapes of dandelion are 

 cut into strips they curl, and when put in a hypertonic solu- 

 tion the curvature is reduced. If the substance enters the cell 

 the original curvature is gradually regained. The rate at 

 which this takes place is regarded as a measure of permeability 

 of the cells to the solute. From such observations Brooks 

 concludes that sucrose and salts of univalent kations bring 

 about a rapid increase of permeability, while divalent and 

 trivalent kations cause a great decrease. The same writer 

 {Amer. Journ. Bot. 3, 483-92, 191 6) comes to a similar con- 

 clusion from measuring the rate of exosmosis of electrolytes 

 from dandelion scapes into distilled water after their immer- 

 sion for 1 5 to 25 minutes in isotonic solutions of sodium chloride, 

 calcium, chloride, and cerium chloride. 



Wodehouse {Journ. Biol. Chem. 29, 453-8, 191 7) points 

 out that the cells of the marine alga Valonia are so large that 

 from each one of them 1 to 5 c.c. of sap can be obtained, a 

 quantity sufficient for performing chemical tests. He found 

 that nitrates and potassium are present in the cell in higher 

 concentration than in the external medium ; sodium, calcium, 

 and chlorides were equally abundant within and without the 

 cell, while magnesium and sulphates, which are present in sea 

 water in notable concentration, are practically absent from 

 the cell sap. The selective permeability thus demonstrated is 

 shown not to be due to the cell wall, which has no selective 

 properties. 



Artzikovskii and Shelyakina {Bull. Acad. Sci. Petrograd, 

 1043-62, 19 1 6) maintain that various acids (hydrochloric, 

 sulphuric, nitric, phosphoric, acetic, etc.) and salts of heavy 



metals in high concentrations (— to AM do not destroy the 



functioning of the cell membrane in Begonia rex. However, 

 the observations of Hind {Ann. of Bot. 30, 223-38, 1916) 

 show that all acids pass rapidly into plant cells, and Stiles 

 and Jorgensen {Ann. of Bot. 31, 415-34, 191 7) snow tnat this 

 absorption, even with very dilute solutions, is accompanied by 



