14 TREE WOUNDS AND DISEASES 



account be looked upon as a substitute for the 

 other. Hollow trees will often flourish for 

 years, for a decayed interior may be surrounded 

 by healthy living wood ; but a broken branch 

 will, to a greater or less extent, mar the beauty 

 of a tree. 



It should be understood that a tree does not 

 cease to grow when it arrives at maturity, for, 

 as long as it is alive, annual layers of wood are 

 developed by the cambium. When, however, 

 maturity is passed, deterioration of the timber 

 takes place, when it usually assumes first a 

 reddish-yellow colour, and finally becomes 

 " foxy " or deep reddish brown. Then comes 

 wasting away of the wood ; the stem gradually 

 becomes hollow as age advances, the process 

 of decomposition being hastened by minute 

 parasitic fungi and insects, which greatly aid 

 in bringing about rot or decay. 



The filling must be adapted to circumstances, 

 and to deal with the entire trunk of a hollow 

 tree is in most cases quite out of the question, 

 both from the point of utility and expense. 

 Short-lived trees, as the alder, birch, and poplar, 

 or such as are liable to sudden attacks of 



