116 KINDS OF STEM. 
If the terminal bud of a stem is continually developed, the 
axis upon which it is placed is prolonged upwards from the © 
earth to its summit, giving off branches from its side, as in most 
Firs ; such a stem has been termed excwrrent. When the main 
stem is arrested in its growth by the process of flowering, 
or some other cause, and the lateral buds become the more 
vigorously developed, so that the stem appears to divide into a 
number of irregular branches, it is said to be deliquescent. These 
different kinds of growth influence materially the general form 
of trees. Thus, those with excurrent stems are usually more or 
less conical or pyramidal ; while those with deliquescent stems 
are rounded or spreading. The general appearance of trees also 
depends upon the nature of the lateral branches, and upon the 
angle which they make with the stem from which they arise. 
Thus, if the branches are firm, and spring at an acute angle to 
the stem, as.in the Cypress and Lombardy Poplar, they are 
erect, and the tree is more or less narrowed ; if they come off at 
a right angle, the branches are spreading, as in the Oak and 
Cedar ; if the angle is very obtuse, or if the branches bend 
downwards from their origin, as in the Weeping Ash and Weep- 
ing Elm, they are termed weeping or pendulous ; or in other cases 
this weeping appearance arises from the weakness and flexibility 
of the branches, as in the Weeping Willow and Weeping Birch. 
The relative length also of the upper and lower branches will 
give rise to corresponding differences in the general appearance 
of trees. Thus, if the lower branches are the longest and be- 
come shorter as they approach the top, the whole will take the 
form of a cone or pyramid, as in the Spruce Fir ; if the middle 
branches are longer than those of the base and apex, the general 
appearance will be rounded or oval, as in the Horsechestnut ; 
if those of the top are the most developed, the form will be 
umbrella-like, as in the Italian Pine. 
Kinps oF STEM AND BrancHEes.—We have seen that the 
stem (page 73), when first developed, always passes upwards, 
while the root at the same time passes downwards. In many 
instances this original direction of the stem is continued more or 
less throughout its life, but in other plants the terminal bud 
either acquires an irregular development, and the stem runs 
along, or remains under, the surface of the ground; or it 
perishes altogether at a very early period, and an axillary 
branch takes its place, which also, by developing laterally, will 
likewise continue near the surface of the ground, or burrow 
beneath it. From these peculiarities in the direction and growth 
of stems and branches, we have a number of modifications which 
we now proceed to describe. These are best treated of, in a 
practical point of view, under two heads, namely, those which 
are aerial, and those which are subterranean. We can, however, 
by no means draw a distinct line between the modifications of 
stem which these two divisions respectively contain, as certain 
