STUDIES OF TREES IN WINTER 



and outside of this the bark. Each year new 

 cells are formed in the cambium layer, the inner 

 ones making new wood, the outer ones new 

 bark, and by counting these annual rings of 

 growth the approximate age of the tree is found. 

 In young trees there is a conspicuous central 

 portion of pith which remains after the tree 

 matures, as long as the heartwood is sound. 

 The lines radiating from the centre to the 

 circumference are called medullary or pith 

 rays and form the " silver grain " of the wood. 

 As the size of the trunk increases, the bark un- 

 able to expand, cracks in fissures or peels in 

 layers, and is pushed off by the tremendous 

 growing power from within. The heartwood 

 is not a living part of the structure and often 

 trees live for years without it, hollow shells 

 with a normal amount of vitality so long as the 

 roots, the cambium layer and the buds are not 

 injured. 



Branches grow from the axillary or lateral 

 buds on the stem, continuing their growth 

 every year by the development and unfolding 

 of new buds, both terminal and lateral. When 

 the growth is carried on by the terminal buds, 

 the tree is more apt to be regular in outline than 

 when these are injured or killed and lateral 

 buds develop the growth instead. Branches 

 6 



