lujlLllHARY 



Volume U X^^^ ■% K Number 7 



The Plant World 



A Maoazine ok General Botany 

 JULY, 1911 



THE RELATION OF THE OSMOTIC PRESSURE OF THE 

 CELL SAP IX PLANTS TO ARID HABITATS. 



Burton Edwvkd Livingsto:v. 



Plant physiology and the various fields of its application 

 are indebted to Hans Fitting * for the first extensive study of 

 internal osmotic pressure as a plant character ecologically re- 

 lated to environmental conditions. Although numerous deter- 

 minations of the magnitude of the osmotic pressure in plant cells, 

 both by the method of plasmolysis and by that of the freezing 

 point, have already been carried out, these have dealt with 

 comparativelv few plants and with restricted ranges of condi- 

 tions. From the hitherto available information, the usual 

 pressure in the cells of the ordinary land and fresh-water plants 

 may be taken as from 5 to 1 1 atmospheres (Pfeffer-Ewart 1 : 

 139), but cases are on record of pressures much outside of these 

 limits. So far as I am aware, the highest pressure hitherto 

 observed in ordinary plants is that of 40 atmospheres, found 

 by Pfeller in the internodes of grasses (citation in Jost-Gibson, 

 p. 419). 



In a very thorough-going study of the osomtic pressures 

 ocurring in the foliage of a large number of plant forms growing 

 naturally in the vicintyof Biskra, Algiers, Fitting finds that the 

 pressure of the cell sap may often reach magnitudes very much 

 higher than those mentioned above. In this study,' the leaf 

 epidermis, or sections of mesophyll — always from leaves gathered 

 in the forenoon of the same day — were tested plasmolytically 



♦Fitting, Hans, Die Wasserversorgung und die osmotischen Druckvcrhalnisse der 

 Wiistenpflanzen. Zeitsclir. f. Bot. 3: 209-75. 1911. 



