64 Journal of the Mitchell Society [August 



come smaller. An osmotic interchange through the cell walls thus 

 accompanies and complicates the simple movement of water, and 

 though millions of cells may intervene there exists a direct osmotic 

 relation between the topmost leaf of the tallest tree and the soil 

 solution at its root tips. 



Although a consideration of the physico-chemical laws of diffusion 

 and osmosis are prerequisite to a thorough understanding of the water 

 relations of plants, especially absorption, diffusion and osmotic pres- 

 sure, yet this hasty resume must suffice for the purposes of this paper. 

 Many investigations have been conducted to determine the influence 

 upon the organism of the medium in which it is grown, but it is only 

 recently that osmotic pressure has been studied in this connection. 

 Among such researches those of Drabble and Drabble, Fitting, Dixon 

 and Atkins, Harris, Gortner and Lawrence should be mentioned. 



A consideration of the factors surrounding the problem and the 

 results which were to be attempted indicated that the study of osmotic 

 concentration in relation to environment should be so conducted as 

 to present as great a diversity of habitats as possible. If, as was an- 

 ticipated, differences in the densities of the sap were correlated with 

 the habitat, the relationship would be sufficiently pronounced to be 

 evident at once. An investigation of the properties of the intra- 

 cellular fluids of forest vegetation on various habitats, in which the 

 supply of available soil moisture and the evaporating power of the air 

 varied greatly, would throw considerable light upon the basic physio- 

 logical problems of silviculture and forest distribution. Chief among 

 these may be mentioned the relative ability of different species to ex- 

 tract water from the soil and retard transpiration through increased 

 sap concentration, the relation of sap density to frost resistance, and 

 the role of the osmotic pressure of the cell sap in the adaptation of 

 exotic species. 



Six series of osmotic concentration tests were made at different 

 times and places in the Wasatch Mountains of Utah. These covered 

 a wide range of habitats (in all about 800 tests) extending from the 

 typically arid alkali flats occupied by greasewood (Sarcodatus ver- 

 miculatus) and shadscale (Atriplex sp.) at elevations of 4,500 to 

 5,500 feet, through the sagebrush {Artemisia tridentata), pinon- 

 juniper {Pinus edulis- Juniper us utahensis), oakbrush {Quercus utah- 

 ensis), and aspen-fir (Populus tremuloides-Pseudotsuga taxifolia) 

 associations to the spruce-fir {Picea engelmanni-Ahies lasiocarpa) 



