58 TIMBER AND TIMBER TREES. [chap. 



the air ; and it is usually started in the standing 

 tree by the loss of a large root or branch, which 

 gradually opens the way to the air and moisture, and 

 eventually, it may be, to minute fungi and bacteria 

 which hasten the processes of decomposition started by 

 the oxygen of the atmosphere. 



Fundamentally, this process of decay is merely a 

 phase of the process of destructive combustion which 

 all organic matter is liable to in contact with oxygen. 

 As the wood loses weight and substance, it shrinks 

 more and more, and so we find cracks of various kinds 

 as described. 



It is, after all, merely the extension of these de- 

 structive processes which result in the hollowing out of 

 old trees ; though in these cases the phenomenon is 

 usually accelerated — and often, indeed, started — by the 

 ravages of certain fungi which gain access through 

 wounds, such as broken branches, gnarled roots, and so 

 forth. 



As before stated, in bad cases the points touch the 

 circumference of the tree ; they even occasionally bulge 

 there, forming a longitudinal rib, varying in length 

 from about a foot to two or three yards. We have thus 

 external evidence of the presence of the star-shake in 

 this extreme case while the tree is yet standing. We 

 can, therefore, from this alone, estimate its value, and 

 prove the correctness of our opinion of it after the -tree 

 has been felled. No one, I imagine, experienced in 

 timber-surveying, would, with the bulging rib in view, 

 care to examine either the top or butt end of the log to 

 satisfy himself of the presence of the star-shake ; the 

 guide is so absolutely certain that we need not fear to 

 trust to it. 



In these last cases, the cause of the radial crack is 



