FROST-CLEFTS. 471 



sap ; and there being no foliage, and in consequence 

 no evaporation, this theory cannot be sustained. 

 Besides, no sap runs from the clefts. The most 

 popular theory attributes this phenomenon to ex- 

 pansion in the act of freezing; but, according to 

 Brunner, ice reaches its greatest bulk at the moment 

 of congelation. At thirty-two degrees Fahrenheit it 

 acquires about one-eleventh of its bulk ; therefore, 

 if a tree becomes cleft at all from this cause, it must 

 be at this moment ; for, as the cold increases, Brun- 

 ner found its volume to diminish. He observed that 

 the linear contraction of ice is one twenty-six thou- 

 sand seven hundredths for every degree Centigrade. 

 But the clefts did not appear until the cold was 

 below twenty-three degrees Fahrenheit ; so that the 

 freezing of the sap could not have been the cause. 



Duhamel, Buffon, and Treviranus entertained the 

 opinion that the stems are burst by the " volume 

 acquired, on congelation, by a mass of moist, decayed 

 wood, or an accumulation of sap in the interior of 

 the tree." Although Dr. Caspary allows that such 

 may sometimes cause a cleft, yet he had never seen 

 an example of it. He had never found ice in the 

 splits, and the decayed wood seemed to be dry. 

 He finds the same difficulties to this theory as to 

 the last : if they cleave for this reason, it should be 

 at the moment of congelation. 



He thus sums up his observations: " The bursting 

 takes place at night by severe frost, not less than 



