8 Characteristics, Structure, Life of Trees 



This thick or outer bark is, therefore, of no direct use in 

 the life of the tree, though indirectly it may be of use in 

 protecting the Hving tissue underneath against heat and 

 cold, against drying out and against mechanical injury. 

 The scraping of bark, so often foolishly practised, is, there- 

 fore, in most cases either useless, or even, as it reduces the 

 protection, injurious. Its only, yet doubtful, usefulness 

 may be found in curtailing the chance for insects to hide 

 their eggs or cocoons; and, under certain abnormal con- 

 ditions, when the tree is "bark bound," the operation of 

 barking or sHtting the bark may then be found useful in 

 removing pressure, although other means of overcoming the 

 trouble are probably better. 



Growth and Form Development. Except in the trees of 

 the palm tribe (which do not increase much in diameter, but 

 start from the seed in nearly full size of girth) the growth 

 of the tree in thickness takes place by division and growth 

 of the cambium cells, annually adding a cone-like envelope 

 over the whole body of the previous years; in cross section 

 these annual envelopes appear as "annual rings." Hence 

 the age of a tree can be determined from the number of rings, 

 if it is cut low enough to include the lirst year's growth. 

 Only under rare conditions does the tree, in countries with 

 a definite growing season, fail to make this annual growth, 

 or does it make apparently two or more such rings. 



The growth in height or in length of branches and in the 

 spreading of the crown is secured by addition of new shoots, 

 which are developed from the buds. These shoots grow 

 in length only during the season in which they are formed, 

 then become rigid, and in these, no more growth in length 

 but only in thickness is experienced in subsequent seasons. 

 The end-bud, which usually terminates the year's shoot, 

 if not lost by frost or drouth during the winter (and in some 



