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 living 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 slitting 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 first 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 
