HERBS.—SH RUBS.—TREES. 115 
rectilineal direction, as in the Passion-flower (fig. 213), where they 
adhere to other bodies by means of little twisted ramifications 
called tendrils, v, v; or in the Ivy, where they emit little aerial 
roots from their sides, by which they cling to neighbouring 
bodies (fig. 225, a, a). Or if such stems twist round other 
bodies in a spiral manner they are said to be twining ; and this 
twining may take place either from right to left, as in some 
Convolvuli (fig. 227), French Bean, and Dodder ; or from left 
to right, as in the Honeysuckle (jig. 226), Hop, and Black 
Bryony ; or first in one direction and then in another, irregu- 
larly, as in the White Bryony. The climbing and twining 
stems of cold and temperate regions are generally herbaceous 
or die annually, although we have exceptions in those of the 
Ivy, Clematis, and Honeysuckle, which are woody. In tropical 
climates these woody climbing and twining stems often occur ; 
these are called lianas or lianes, and they frequently ascend to 
the tops of the loftiest trees, and then either descend to the 
ground again, or pass to the branches of neighbouring trees. 
The stem has received many names according to its nature. 
Thus it is called a cawlis in plants which are herbaceous, or die 
down annually to the surface of the ground; a trunk, as in 
trees, where it is woody and perennial ; a culm, as in most 
Grasses and Sedges, where it presents a jointed appearance ; 
and a caudex or stipe, as in Tree-ferns and Palms. 
Herbs, Shrubs, and Trees.—From the nature, duration, and 
mode of branching of stems, plants have been arranged from the 
earliest periods in three divisions, called, respectively, Herbs, 
Shrubs, and Trees. Thus, those plants which have stems that die 
down annually to the surface of the ground are called herbs ; 
while those with perennial aerial woody stems are denominated 
trees or shrubs according to circumstances, as described below. 
Herbs are also further characterised as annual, biennial, and 
perennial. Thus they are annual when they only live through one 
season, that is, between the spring and winter ; biennial, when 
they spring from seed in one season, and die in the second, after 
producing flowers, fruit, and seed ; and perennial, when they ger- 
minate from seed in one season, and continue to live through 
a succession of years, and annually send up an herbaceous 
stem. The term tree is applied if the branches are perennial 
and arise from a trunk. When the branches are perennial and 
proceed directly from, or near to, the surface of the ground, with- 
out any trunk, or where this is very short, a shrub is formed ; 
this when low and branched very much at the base, is denomi- 
nated abush. The term wndershrub is also applied to a small shrub 
which is intermediate in its characters between an ordinary 
shrub and an herb; thus, when some of its branches generally 
perish annually, while others are more or less permanent. All 
the above kinds of stems are connected by intermediate links, 
so that in many cases they are by no means well defined. 
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