1912. 



PUBLIC DOCUMENT — No. 31. 



Ill 



filling as a means of preventing the access of water between 

 the cement and the wood, hut have fonnd it practically impos- 

 sible so far to prevent the bleeding of frost cracks or cavities in 

 trees. There is no substance now in use which can successfully 

 overcome the pressure exerted by the sap, which is bound to 

 exude under certain conditions. 



During the winter of 1907 IMr. E. G. Bartlett, at that time 

 assistant in the laboratory, at my suggestion made measure- 

 ments of the opening and closing of the orifices of some large 

 frost cracks on the south side of elm trees located on the college 

 campus. In the following table are given the results of these 

 measurements, together with the mean temperature for the same 

 period. The meteorological data were taken from the local sta- 

 tion on the college grounds, and not a great distance from the 

 trees. 



Table showing Variation in the Width of Frost Cracks in Elm Trees 

 {Ulmus Americana). 



