344 



DIFFERENTIATION OF LEAF TISSUE FLUIDS 



tissue was collected in large test-tubes and squeezed as completely as 

 possible after freezing to render the tissue permeable as has been 

 shown to be necessary by Dixon and Atkins and by ourselves. The 

 freezing point lowering, A, was determined in the usual manner. Cor- 

 rection was made for the ice separating on undercooling. The spe- 

 cific electrical conductivity, K, of the centrifuged sap was measured at 

 30°C. in a Freas conductivity cell, standardized by considering the 

 conductivity of 0.1 n KCl to be 0.01412 reciprocal ohms, by means 

 of the ordinary meter bridge wire. 



The determinations for each species were then averaged and the 

 deviation of each determination 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 — were discarded, and a new average with 



A 



TABLE I. 



deviations < ± 20 per cent was determined. The statistical constants 

 are, therefore, based on carefully selected averages whenever more 

 than a single determination was available for a species. Determining 

 the averages from the protocols of measurements we have the results 

 for the three growth forms, and for a combination of the two groups 

 of ligneous plants set forth in Table I. 



The constants show that the tissue fluids of both trees and shrubs 

 are characterized by a far greater freezing point lowering than are 

 those of herbaceous plants. The mean freezing point lowering of the 

 leaf tissue fluids is greater, although perhaps not significantly greater 

 in comparison with its probable error, in arborescent than in shrubby 

 species. The differences between trees and herbs, shrubs and herbs, 

 and all ligneous plants and herbs are several times as large as the 

 probable error of the difference and so unquestionably significant. 



