172 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



in the second rather than in the third group, it seems 

 probable that the value 52 is a misprint for 32. 



Fitting points out that the lowest osmotic pressures 

 are found in annuals, and the highest in bushes. Of the 

 latter class ten were found to have pressures of about 

 100 atmospheres, six of them having sap rich in sodium 

 chloride. 



He also criticizes the cryoscopic method, and calls atten- 

 tion to the alterations which take place in the expressed 

 sap, as a source of error, mentioning in particular the 

 browning due to oxidation.* But this and other similar 

 changes are, in fact, quantitatively insufficient to cause 

 any appreciable error, as has been shown by direct experi- 

 ment. Cryoscopic measurements combined with deter- 

 minations of electrical conductivity would, indeed, have 

 thrown much light upon the proportions in which electro- 

 lytes and non-electrolytes were concerned in producing 

 the high pressures met with in desert plants . It is , however, 

 obvious that an investigator can apply the plasmolytic 

 method while travelling under conditions which would 

 render the more elaborate technique of cryoscopy quite 

 impossible. 



To the low osmotic pressure of some annuals Fitting 

 attributes the fact that in particularly dry years they do 

 not thrive. The bushes, however, are able to draw water 

 from the soil moisture which exists a few inches below 

 the dry upper layer. 



* Diese und alle ahnlichen ausschliesslich an ausgepressten Zellsaften 

 gewonnenen Resultate diirften aber nur selten Riickschlusse auf die 

 osmotischen Drucke in den unverletzten Zellen erlauben: Autolytische 

 imd andere Prozesse sind ja wahrend und nach der Zertrummerung der 

 Zellen ganz unvermeidlich. Geben doch die Verf. selbst an, dass die 

 Zellsafte haufig braun warden. Es ist zu bedauern, dass in zahlreichen 

 neueren auslandischen Arbeiten die kryoskopische Methode zur Ermitt- 

 lung osmotischer Drucke ohne Grund so sehr bevorzugt wird. 



