J. A. HARRIS, R. A. GORTNER, AND J. V. LAWRENCE 345 



Expressing the differences in per cents of the values for ligneous 

 forms, we note that the value for trees and shrubs is 30.46 per cent 

 higher than that of herbaceous plants. These results are, therefore, in 

 excellent agreement with those found in the Arizona deserts and in the 

 Jamaican rain forest. 



The constants for specific electrical conductivity show that the con- 

 ductivity for shrubs is slightly lower than that for trees. The differ- 

 ence is, however, smaller than its probable error. The diJfferences 

 between the conductivities of the fluids of trees and herbs, shrubs and 

 herbs, and both ligneous forms and herbs are several times as large 

 as their probable errors and show that the conductivity is distinctly 

 higher in herbaceous than in ligneous species. 



The ratio of conductivity to freezing point depression is much 

 smaller in both trees and shrubs than it is in herbs. The mean 



value of — is lower in trees than in shrubs, although the difference 

 A 



cannot be considered significant in comparison with its probable error. 



The ratios (X 10^) are 9,092:17,674 in the case of trees and herbs and 



9,529:17,674 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, and we obtain an average of — in all ligneous plants of 9,378 



A 



dz 292 as compared with 11 ,61^ ± 282 in herbs. Thus the ratio — 



A 



is about 90 per cent higher in herbaceous than in ligneous plants. 



The foregoing results show clearly that the osmotic concentration 



is higher while the electrical conductivity is lower in the tissue fluids 



of ligneous than in those of herbaceous species. Because of the wide 



geographic range and the great diversity of conditions (xerophytic, 



mesophytic, and hygrophytic) under which the investigations on 



osmotic concentration were carried out there can be no reasonable 



doubt that the differentiation of ligneous and herbaceous plants with 



respect to the magnitude of their osmotic concentration is a general 



biological law. Until confirmed by investigations in other regions 



presenting different conditions for plant growth — ^investigations which 



are now in progress — the results for conductivity cannot be asserted 



to be of universal validity. 



