112 



EXPERIMENT STATION, 



[Jan. 



Table shoiving Variation in tfie Width of Frost Cracks in Elm Trees 

 (Ulmus Americana) — Concluded. 



Measurements were not taken on February 10, 17 and 24 (Sunday). The remainder of March 

 the cracks were too small to measure conveniently. 



In the following diagram are shown graphically the variations 

 in the opening and closing of frost cracks hased upon the aver- 

 age measurements of tree No. 1 and No. 2 ; also the barometer, 

 mean temperature and mean relative humidity curve. 



It will be noticed that the barometer and temperature curves 

 coincide closely with those given by the opening and closing of 

 the frost cracks, and the same is true to a certain extent of the 

 curve given by the relative humidity. The temperature curve 

 is based upon the mean of the maximum and minimum for each 

 day. 



During the periods of low temperature the cracks opened, and 

 closed when the temperature was higher. They open wider in 

 February than in ]\Iarch, as shown by the higher readings in the 

 table. 



The relative mean humidity curve in general corresponds 

 with that of the opening and closing of the frost cracks. When 



