RECENT ADVANCES IN SCIENCE 385 



of the cells were thus obtained, thus confirming the correctness 

 of the method. 



The method was first called by Hofler the plasmolytic- 

 volumetric method. In the second paper (" Permeabilitatsbe- 

 stimmung nach der plasmometrischen Methode," Ber. deut. bot. 

 Ges., 36, 414-22, 191 8) this rather cumbersome name is con- 

 tracted to the term plasmometric method. In this paper it is 

 shown how the method can be adapted for the determination 

 of the permeability of plant cells. The principle of the method 

 is as follows. Suppose a cell is completely plasmolysed in a 

 solution and the degree of plasmolysis is Pi. If the plasmolysing 

 substance penetrates into the cell the latter will gradually 

 become deplasmolysed. Suppose that after a time the degree 

 of plasmolysis is P2. Then, if the external concentration of the 

 solution is C, and the osmotic concentrations of the cells cor- 

 responding to the two degrees of plasmolysis are Oi and Oa, 

 we have Oi = CPi and O2 = CP-^, whence O^—Oi = (P2 — Pi) C. 

 The change in osmotic concentration of the cell per unit time 

 is then taken as a measure of the permeability of the cell. 



In his third paper (" Uber die Permeabilitat der Stengel- 

 zellen von Tradescantia elongata fiir Kalisaltpeter," Ber. deut. 

 bot. Ges., 36, 423-42, 191 8) Hofler records some measurements 

 of permeability made by his method. The tissue employed, 

 parenchymatous cells from the stem of Tradescantia elongata, 

 was somewhat permeable to potassium nitrate. One of the 

 striking results obtained in this work is the extreme variability 

 in permeability of even neighbouring cells of the same tissue, 

 measurements of apparently similar cells under the same condi- 

 tions varying from, for example, 0*016 to o"oo2. Hofler em- 

 phasises the advantage of his method over those previously 

 employed, in that the actual permeability of single cells is 

 measured, whereas in earlier methods this is not the case. 



In a fourth paper (" Uber den zeitlichen Verlauf der Plas- 

 madurchlassigkeit in Salzlosungen. I.," Ber. deut. bot. Ges., 37, 

 314-26, 1919) the course of intake of potassium nitrate by stem 

 cells of Tradescantia elongata was investigated. The per- 

 meability of the same cell was found to undergo reversible 

 changes in its permeability, the cause of which is not at all 

 obvious, since these changes in permeability may be quite 

 different in different cells exposed to the same conditions so that 

 the changes do not appear to be due to the action of the external 

 solution. The fact observed by Fitting, in the case of epiderrnal 

 cells of Rhoeo discolor, that there is a decrease in permeability 

 after long action of the salt solution, was observed in some, 

 but not all, cells examined by Hofler, but when this decrease in 

 permeability occurs at all, it comes about much later in Trade- 

 scantia elongata than in the cells examined by Fitting. In the 



