CHAPTER I. 
ON THE GROWTH AND STRUCTURE OF TREES. 
THE stems of Exogenous* trees may be described as 
of one uniform structure and mode of increase, and 
are usually very firm, yielding the most solid and best 
description of timber, their solidity and strength’ fitting 
them admirably for use in carpentry, and for many 
domestic purposes. 
The most common form of stem is the cylindrical, 
but it is occasionally found grooved or fluted, and not 
unfrequently flattened, approximating to an oval; the 
cylindrical form being, for most purposes, the best for 
conversion into beams, joists, boards, &c. 
Botanists speak of the stem as the “ ascending axis” 
of a tree, from its taking an upward direction and giving 
off branches. In the Elm, these branches take an 
oblique upward direction; in the -Birch, they are also 
oblique, slightly pendulous, and flexible; those of the 
Willow are somewhat oblique, with the lateral branchlets 
pendulous and drooping in graceful curves; in the 
* Exogens are a vegetable class, which augment their woody matter by 
additions to the outside of that which is first formed ; as long, therefore, 
as they grow a new layer of wood is added to the outside of the previous 
growth. The Endogen class—i.¢., Palms, &c. &c.—differ from the above, 
in having their substancé formed by successive additions from the inside. 
