DENSITY OF THE CELL SAP OF PLANTS IN RELATION TO 

 ENVIRONMENTAL CONDITIONS 



By C. F. KoRSTiAN 



Every observer of plant life in the mountainous regions of the 

 West is familiar with the altitudinal zonation of the different types 

 of vegetation ranging from the characteristic xerophytic greasewood- 

 shadscale and sagebrush deserts or grasslands at the base of the moun- 

 tains to the mesophytic spruce-fir forests common on the summits. 

 The causes of this zonation have been investigated by ecologists by 

 analysis of the component factors of the environment. One of these 

 factors which was studied recently by the writer in Utah — the density 

 of the cell sap of plants in relation to environmental conditions — has 

 thrown considerable light on this rather complex problem of plant 

 succession. Although the detailed results might not be of sufficient 

 interest to warrant presenting them before this Academy, yet the 

 general principles are of such a broad scope as to suggest the existence 

 of a somewhat similar though possibly very much less pronounced re- 

 lation in North Carolina. It will be impossible, in the time available, 

 to more than touch upon the salient features. A more detailed report 

 will appear at a later date. 



Among the relations which plants bear to their environments, 

 those of water are of the first importance. None of the environmental 

 factors is of more significance than the forces with which the soil 

 withholds and the air withdraws water from the plant. The passage 

 of water through the organism, however, is not a simple process. It 

 is complicated by the presence of substances in solution, and this in- 

 volves osmosis, or the movement of the solvent through the cell wall 

 membranes from the weaker to the stronger solution. 



The laws of osmosis set forth explicitly that a substance in solution 

 tends to distribute itself uniformly throughout the entire volume of 

 the solvent. In the plant cell no absorption will take place when the 

 concentration of the solution outside is equal to that within the cell 

 vacuole, and if the outside solution is the more highly concentrated 

 water will actually be withdrawn from the vacuole, which will be- 



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