12 PROTECTION OF WOODLANDS. 



actually in course of progress ; it is by no means always effective, 

 but only when the actual damage taking place is comparatively 

 trifling. 



8. Frost-shakes. 



In certain species of trees frost-shakes, or longitudinal clefts 

 or fissures, not infrequently appear on the older classes of stems 

 as the peculiar effect of hard winter frost. Beginning near the 

 ground, they are sometimes only a yard or two long, but at other 

 times extend into the crown, and penetrate from the circumference 

 to a greater or less depth inwards in the direction of the medul- 

 lary rays, often to the very core of the stem. Although not 

 interfering with the vital energy, increment, or development of 

 the tree, they render the timber less suitable for various technical 

 purposes, and not infrequently afford an opportunity for the 

 entrance of fungoid spores into the stem, thereby leading to 

 subsequent disease. 



The occurrence of frost-shakes is due to the contraction of the 

 wood which takes place during great cold, much in the same way 

 as contraction of timber is due to the withdrawal of water when 

 it is becoming seasoned. During severe cold not only the water 

 contained in the elementary parts of the wood becomes frozen, 

 but also the water in the cell-walls, whilst at the same time tl 

 is drawn into the interior of the cells, so that the substance 

 which the cellular walls are formed is diminished in volui 

 and contracts, the contraction being greater tangentially thj 

 radially, and greater in the outside zones with their 

 quantities of water than in the drier heart-wood. Whenever this 

 shrinkage exceeds a certain limit, a sudden division of the 

 woody-fibrous tissue takes place in the direction of the medul- 

 lary rays, the separation being accompanied with a great noise, 

 according to direct observations, 1 and the frost-shake is formed. 

 When the thaw succeeds, and expansion again takes place, the 

 fissure closes and becomes overgrown by the new annual zone in 

 the following summer, but it is usually opened again during the 

 next winter, even by a moderate degree of cold ; when, however, 

 several mild winters pass by without causing the fissure to 



1 Precisely the same occurs, owing to shrinkage from heat, in the bamboo forests of 

 Burma, during the hot months of March and April, when the halms burst with loud 

 noise, often as loud as the report from a pistol. Trans. 



