494 



SCIENCE 



[N. S. Vol. LII. No. 1351 



cited ; the mistake is the one practical breeders 

 have so commonly made for generations past 

 of generalizing- from a few instances. One 

 often wishes it were as easy to inculcate into 

 students the principles of genetics as it is to 

 gain a wide acceptance of theories that have 

 no scientific basis and calmly disregard any 

 demands for proof. 



L. J. C. 



SPECIAL ARTICLES 



ON THE RELATIONSHIP BETWEEN FREEZING 



POINT LOWERING, A, AND SPECIFIC 



ELECTRICAL CONDUCTIVITY, K, OF 



PLANT TISSUE FLUIDS 



The problem of the contribution of non- 

 electrolytes, of undissociated molecules of 

 electrolytes, and of dissociated ions of electro- 

 lytes to the depression of the freezing point, 

 A, in terms of which osmotic concentration is 

 usually measured, is one of considerable bio- 

 logical importance. "We desire to know, for 

 example, whether an observed difference in 

 the osmotic concentration of the tissue fluids 

 of a species growing in two different habitats 

 is due primarily to differences in the quanti- 

 ties of electrolytes absorbed from the medium 

 or to differences in the quantities of organic 

 substances elaborated. The same .question 

 naturally arises when one is comparing the 

 osmotic concentration of the tissue fluids of 

 different species in the same habitat. 



In the mixed solutions with which the biol- 

 ogist has to deal the problem presents serious 

 difficulties. In certain cases some progress 

 may be made by determining the correlation 

 between the freezing point depression. A, and 

 the specific electrical conductivity, K. 



As a specific illustration we may take the 

 relationship between osmotic concentration 

 and electrical conductivity in a series of 

 plant species growing in the non-halophytic 

 habitats of the north shore of Long Island.^ 



In a series of 19 species of trees, 36 species 

 of shrubs, and 162 species of herbs both A and 



1 Protocols of data and full details are given in 

 a paper in press in the Journal of Physical Chem- 

 istry. 



K are highly variable. The coefficients of 

 variation, i.e., 100 cr/m, where o- is the stand- 

 ard deviation and m the means are: 



A K 



Trees 21.46 28.49 " 



Shrubs 18.46 28.03 



Trees and shrubs . . . 20.20 28.27 



Herbs 23.46 25.33 



Our problem is to determine whether 

 higher values of K are associated with higher 

 values of A, or whether within each of thrae 

 growth forms^ these two constants of the solu- 

 tion are essentially independent. 



Determining the correlation coefficients by 

 the usual product moment method we have 

 the following measures of relationship be- 

 tween the magnitudes of K and A in the 

 various series. 



For trees, iV = 19, r = + 0.127 =!= .152 



For shrubs, i\^ = 36, r = — 0.079 ± .112 



For trees and 



shrubs, iV = 55, r = + 0.022 ± .091 



For herbs, iV = 162, r = + 0.150 ± .052 



For ligneous plants the correlations be- 

 tween A and K are low and statistically in- 

 significant in comparison with their probable 

 errors. The coefficient for shrubs is actually 

 negative in sign. That for trees and shrubs 

 together is sensibly zero. The coefficient for 

 herbaceous plants is also low but may indicate 

 a slight relationship between the two con- 

 stants, higher values of A being associated 

 with higher values of K and vice versa. 



These results show that, in the vegetation 

 of the glacial moraines of Long Island at 

 least, there is practically no relationship be- 

 tween the concentration of ionized electro- 



2 It is necessary to separate the growth forms, 

 since, as shown in detail elsewhere (Harris, Gort- 

 ner and Lawrence, loe. cit.), the growth forms are 

 highly differentiated with respect to both A and K. 

 The actual means are: 



A Ky. io» 



Trees 1.292 11,213 



Shrubs 1.177 10,770 



Trees and shrubs . . 1.217 10,923 



Herbs 0.846 14,308 



