94 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



is not as accurate as the cryoscopic method for the deter- 

 mination of osmotic pressures, the method of plasmolysis 

 is nevertheless of great value in obtaining information 

 quite inaccessible by cryoscopy. 



It seems that the hsematokrit of Koppe (1895), employed 

 by Hedin (1895) and Hamburger (1902) and others for 

 investigations on the volume changes in blood-corpuscles, 

 might also be used for yeast. Euler, however, preferred 

 to use the plasmolytic method, for the haematokrit gives 

 average results just as the cryoscopic method does. 



COMPARISON OF THE CRYOSCOPIC AND PLASMOLYTIC 

 METHODS OF MEASURING OSMOTIC PRESSURES OF 

 PLANT CELLS. 



As has been pointed out on p. 85, the application of 

 pressure alone is not sufficient to obtain the unaltered sap 

 of the vacuoles. The cells must be rendered permeable by 

 intense cold. Through want of knowledge of this -factor, the 

 cyroscopically determined values recorded in all the papers 

 by Dixon and Atkins up to 1912 inclusive are too low, 

 by amounts varying from a few per cent., in soft tissues 

 such as potato tubers, up to several hundred per cent, in 

 a tough leaf such as that of Chamcerops humilis. The 

 same criticism applies equally to the experiments of 

 Sutherst (1901), Cavara (1905), Heald (1902), Nicolosi- 

 Roncati (1907), Trinchieri (1909), Marie and Gatin (1912), 

 and Ohlweiler (1912). It is of course obvious that deter- 

 minations of electrical conductivity and chemical analyses 

 of such pressed saps are no less vitiated than are those of 

 osmotic pressures. The results obtained with a particular 

 organ of any plant under varying conditions seem, how- 

 ever, to be quite truly comparable. 



Since the source of error due to alterations in concentra- 

 tion induced by pressure can now be avoided, cryoscopy 



