CHAPTER XIX 
STEMS 
224. Definition. — The stem is that part of the plant 
which forms the connection between the roots and the leaves. 
It is adapted to its work (1) in being compact and sturdy, 
enabling it to bear weight; (2) in branching, to afford a 
larger number of points for the attachment of leaves; 
(3) (in some cases) in being provided with thorns or briers, 
as in the blackberry and rose, to protect it from being injured 
by animals; (4) in being covered with a strong epidermis 
or, in woody stems, with bark which protects it from outside 
injury and keeps it from drying up; (5) in plants which 
grow in the water, in having large air spaces to carry air 
to the roots which lie in the mud at the bottom of the water. 
An underground stem can always be distinguished from 
a root by the buds of new leaves or the scales of old ones, 
although in some the leaves are reduced to mere scales, as 
in the potato. Underground stems usually send up aerial 
shoots. They often have an advantage over an aerial stem 
in being better protected. Some plants make use of the 
underground stem in propagating themselves (see page 305). 
225. Position of Stems. — Stems assume a variety of posi¬ 
tions, but that which serves the purpose of most plants best 
is the upright, independent position. Any tree illustrates 
this kind of stem. A few which are upright keep that 
position by twining or by clinging to an upright support, 
which may be some other plant. These plants have com¬ 
paratively weak stems. Creeping or trailing stems lie on 
the ground with only the tip erect. This position is illus- 
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