136 J. A. Harris, R. A. Gortner and J. V. Lawrence 



9092 : 17674 in the case of trees and herbs and 9529 : 17674 

 in the case of shrubs and herbs. Since the ratio does not 

 differ significantly in trees and shrubs it is quite proper to 

 combine them. The average value of K/ A X io 6 in all ligneous 

 plants is 9378 == 292 as compared with 17674 =*= 282 in 

 herbs. Thus the ratio K/ A is about 90 percent higher in 

 herbaceous than in ligneous plants. 



It seems desirable from the physiological side to deter 

 mine whether conductivity or osmotic concentration is more 

 nearly a constant for the species of a region. Furthermore, 

 it is of interest to determine whether either of the three physico- 

 chemical constants considered is significantly more variable 

 in one class of plants (trees, shrubs, or herbs) than another. 



Comparison of the variability of electrical conductivity 

 and of osmotic pressure can only be made by means of the 

 relative variation constants. The differences in the coeffi 

 cients of variation of K and A for the three growth forms are 

 given in Table VIII. 



TABLE VIII 



Difference in Coefficients of Variation of Electrical Conductivity 

 and Freezing Point Lowering 



Growth form 



Difference 

 C. V._ C. 



Trees 



Shrubs 



Trees and Shrubs 



Herbs 



7.03 4.16 

 9-57 dh 2.84 

 8.07 =*= 2.38 

 1.87 1.36 



The comparison shows that for each of the growth forms 

 investigated the variability of electrical conductivity from 

 species to species is greater than that of osmotic concentra 

 tion. The differences are conspicuously greater in ligneous 

 plants (in which the conductivity is on the average small as 

 compared with the osmotic concentration) than in herbaceous 

 species in which the electrical conductivity is both absolutely 

 and relatively much larger. As a matter of fact, the varia- 



