32 TIMBER AND TIMBER TREES. [CHAP. 



centric layers, and probably arises from the sap failing 

 to possess some of the elements necessary for uniting 

 the new layer to that of the previous year's growth. 

 This deficiency of the cohesive matter between the 

 woody layers is supposed to result from sudden changes 

 of temperature, from the roots passing through a 

 peculiar vein of soil, and even from frosts ; violent and 

 sudden gusts of wind and storms may also help to 

 produce it. 



It will sometimes happen that only a portion of a 

 layer is detached, making the segment of a cup; at 

 other times, a small part of several layers ; and again, 

 in some instances, we find that the disjunction is not 

 complete, owing to there being a few fibres remaining to 

 connect the two layers. When, however, it assumes its 

 worst shape, that is, when the ring or cup is perfect, it 

 will in all probability be found to pervade the greater 

 part, if not the whole tree, evidence of it being fre- 

 quently traceable in the remotest branches. 



Experience has shown that with only a segmental 

 cavity open, there is not much to fear, as it seldom 

 extends far up from the root ; any log, therefore, not 

 having more cup-defect than this, may without hesi- 

 tation be converted into plank, board, or scantling ; 

 but if one or more complete cups be present, especially 

 if they are large, it could not safely be sawn longi- 

 tudinally down the middle, as the centre or cup part 

 would drop out, leaving in each half a deeply-grooved 

 channel, equal to the semi-diameter of the cup-defect. 

 The log in this case could, therefore, only be used 

 advantageously by appropriating it to some purpose, 

 where the full growth might be employed. 



The cup-defect occurs in perfectly sound and healthy- 

 looking trees, and there is not anything to indicate its 



