33. 



The relative hiimidity of the air was measured 

 "by means of the sling psychrometer, which was used 

 not by whirling it, as is commonly done, "but by taking 

 the instrument out of its case and hsinging it on a 

 nail against the tree trunk where it was fanned by 

 as uniform a swing of the arm as possible, This method 

 made it possible to obtain the percentage of relative 

 humidity close to the trunk or branch on which tne 

 ferns live .The percentage of relative humidity was 

 calculated from the psychrometric tables^ 



The evaporating power of the air in the immediate 

 vicinity of the stem was measured by means of ^h^ 

 Livingston standardized spherical porous-cup alanometers 

 which were set up with the non-rain absorbing mountings 

 as described by Livingston and Tj^one (l7)oThe atmometers 

 were set up in pairs at each exposure at different 

 heights and were read once each twenty four hours. 

 After each reading the spheres were brushed and washed 

 with 95^ alcohol to remove any possible spores o r 

 dust, The evaporation was measured voliometrically in 

 cubic centimeters. 



On ftuercus stellata the temperature of the bark 

 was also measured in addition to the other factors, This 

 was done by boring a hole in the bark large enough 

 to hold the bulb of a thermometer, Between readings 



