CHAPTER III 



DEFECTS OF WOOD. 



Ik every stage of their growtli trees are liable to miscliances, from 

 defects of soil or climate, from accident, or from the attacks of 

 fmigi, of insects, or of other animals. Some of these mischances have 

 permanent and important effects upon their wood. Although, in 

 healthy surroundings and in the absence of external injury, there 

 is no very definite hmit to the longevity of any species of tree, after 

 it has reached maturity a certain deterioration generally shows 

 itself at the centre of the trunk, which will subsequently manifest 

 itself as decay. After felling, shrinkage in the process of drying and 

 the attacks of species of fungi, mostly differing from those that 

 injure growing trees, develop further defects in timber of the very 

 gravest practical import to the consumer. 



The attacks of insects or of fungi upon the leaves of trees, though 

 they may prove fatal to seedhngs, have generally in later stages of 

 growth merely the effect of injuring the nutrition of the plant. They 

 may thus diminish the amount of wood formed in the season, and 

 may, therefore, be of first-rate importance to the forester or timber- 

 grower, but do not in general concern the timber-user. 



Cup-shake. — ^When, however, the caterpillars of some moths, 

 such as Tortrix viriddna, entirely destroy the young leaves of the 

 Oak in June, though the tree may put out new leaves in July and 

 August, it will only do so at the expense of wood-forming reserve- 

 materials, and there may possibly result so complete a check to 

 the nutrition of the tree that the wood of one year may fail to cohere 

 to that of the preceding season, a cup-shake or ring'Shahe being pro- 

 duced (Fig. 37). 



Such a separation between successive annual rings-a defect 

 seriously interfering with the conversion of timber into planks — 

 is, however, undoubtedly produced for the most part by various 

 other causes, and may be briefly here described. It occurs ia 

 various species, such as Hazel, Oak, Poplar, Pitch Pine, and Lignum- 

 vite, and seems to some extent local. The Oaks of SicQy, for 

 instance, a variety of our British species, Quercus B6bur, and those 



55 



