34 TECHNICAL PROPBRTIES OP WOOD. 



which the zones can play upon one another is passed, or (c) heavy 

 GoncTission when the tree itself is felled or another large tree falls 

 up against it, or (d) shrinking from loss of moisture of the en- 

 closed cylinder of wood. Such being the case, it is evident that 

 trees in which the vessels are mostly grouped together along the 

 inside edge of each concentric ring, are most liable to cup-shakes. 

 Since a great many of our species have not even any distinct 

 rings of growth, cup-shakes are not much to be feared in India. 

 As we might expect, cup-shakes affect more frequently large than 

 small trees (since the former can bend less), and the lower than 

 the upper part of the stem (since it is at the lower part that most 

 bending takes place and the wood is least uniform in structure). 

 The wood in the cracks of cup-shakes is not always decayed, since 

 it is never exposed to the air. The extent to which cup-shakes 

 render timber unfit for use depends on the number and length 

 of the shakes. Badly shaken wood falls to pieces when sawn 

 up. Even a single shake, if it extends all round the circumference, 

 reduces the thickness of the useful timber by the thickness of the 

 trunk outside the shake. 



"Not unfrequently, in very severe climates, the trunk of a tree is 

 abundantly affected both by radial and cup-shakes, in which case 

 the wood is fit only for burning (see Fig. 4). 



Fig. 4. 



Exaggerated case of combined radial and cvp-ihaiet, 

 with incipient decomposition, (After Gayer), 



