Osmotic Concentration and Electrical Conductivity, Etc. 127 



desirable. To avoid weighting the species upon which more 

 than a single determination had been made, species averages 

 are used whenever possible. These were determined as fol 

 lows.* The whole of the data which had been accumulated 

 at various times during the two years were arranged together 

 by species and all determinations which seemed obviously open 

 to criticism were thrown out. The determinations for each 

 species were then averaged and the deviation of each determina 

 tion from the average for the species was calculated. All 

 numbers which showed a deviation of more than 20 per 

 cent for either A, K, or */ A, were discarded, and a new aver 

 age with deviations &amp;lt; == 20 percent determined from the 

 remainder. 



The inclusion of determinations differing from the 

 average by as much as 20 percent might at first seem to 

 represent great laxness of selection. One must remember, 

 however, that these variations represent more than the errors 

 of experimental measurement. They include all the differ 

 ences due to seasonal and environmental influence as well 

 as the errors of random sampling in the collection of the tis 

 sues. Thus the limits chosen probably represent rather 

 stringent instead of lax selection. The detailed data are 

 shown in Table IV. 



Determining the usual statistical constants from the 

 protocols of measurements we have the accompanying re 

 sults (Table V) for the three growth forms, and for a com 

 bination of the two groups of ligneous plants. 



The constants in Table V show that the mean freezing 

 point lowering of the leaf tissue is greater, although perhaps 

 not significantly greater in comparison with its probable 

 error, in arborescent than in shrubby species. The tissue 

 fluids of both trees and shrubs are characterized by a far 

 greater freezing point lowering than those of herbaceous 

 plants. The differences between trees and herbs, shrubs and 

 herbs, and all ligneous plants and herbs are everal times as 

 large as the probable error of the difference and hence un 

 questionably significant. 



