140 



PROPERTIES OF WOOD. 



it is termed ring-shake, and will be described in the next 

 section. 



Frost-crack is a radial crack occurring on a standing tree 

 at very low temperatures. This form of damage is commoner 

 on sweet-chestnut, oaks, walnut, ash, lime, poplars, elms and 

 maples than on conifers. Of the latter, the silver-fir suffers 

 most and Scots pine and spruce less. It is very rare with 

 beech and aspen. 



[Turkey-oak suffers more from frost-crack than does 

 sessile oak and the latter more than 

 pedunculate oak, while Mathey states 

 that Quercns tardissima suffers less than 

 ordinary pedunculate oak. Fuller details 

 about frost-crack are given in Vol. IV. 

 -Tr.] 



K. Hartig explains the cause of frost- 

 cracks, as follows : during frost, water 

 leaves the cell-walls the more abun- 

 dantly the lower is the temperature, 

 until owing to the consequent drying 

 of the wood, the latter cracks. Accord- 

 ing to Mayr, this explanation is wrong. 

 All physical and mechanical phenomena 

 in frozen wood, as well as Mayr's own 

 experiments, show that water remains 

 in the tissue walls of frozen wood. 

 The cracking of the stem at very low 

 temperatures (about- 25 C. or -13 F.) 



is due to contraction by loss of heat and this results 

 naturally in a radial crack, for the outer layers become coldest 

 and contract the most. When the weather becomes warmer, 

 the crack closes, in the next growing-season the wound is 

 occluded, but the crack opens again the next cold winter 

 and the repetition of this cracking and occluding produces the 

 projecting frost-rib (Fig. 59). Generally such stems are 

 useless except for cleaving. 



[Frost-cracks are quite common in Windsor Forest, both in 

 oaks and sweet-chestnut trees, though the lowest temperature 

 recorded in 1,1 K-. open at Cooper's Hill, close to the forest and 



Fig. 59. Frost-crack and 

 frost-rib. The other 

 cracks on the trans- 

 verse section are due 

 to desiccation. 



