INTRODUCTION 
generally takes an ascending direction ; or it may climb, so as to get 
to light and air above surrounding plants without the necessity of 
great increase in size to support its increased length. Stems climb either 
by twining round others, as in the Bindweeds; by putting out adventitious 
roots, as in the Ivy; by hooked prickles, as in Roses and Brambles; 
by twisting their leaf-stalks round other stems, as in Clematis ; or by 
special organs known as tendrils , which respond to contact by becoming 
spirally coiled. Tendrils may either be branches of the stem, as in the 
Grape Vine, or in other cases some part of a leaf modified for this 
purpose, as in Peas and Vetches. 
Though usually round in section, the stem may be angular, being, 
for example, triangular in Sedges and square in the St. John’s-worts and 
in the Labiate Family. As in these cases the leaves spring from the 
angles of the stem, the shape of the latter is closely connected with 
the arrangement of the former, the leaves of Sedges forming three vertical 
rows up the stem and those of the St. John’s-worts, which are given 
off in pairs at each node, forming four. While young, herbaceous stems 
are generally green, and thus perform the same functions as the leaves; if 
perennial they commonly lose this colour at the close of their first year’s 
growth owing to the formation of cork. The surface may be free from 
hairs and smooth or glabrous , as in the Spindle-tree ; polished, as in 
Lilies ; downy, as in the Hazel ; or bristly, as in the Teazle. The 
Broom is an example of the long whip-like fluted green stem, with 
reduced leaves, characteristic of dry conditions. 
Plants with one main woody stem ten feet or more in height are 
termed trees ; those that branch freely near the ground, shrubs; or if less 
than three feet high, undershrubs. The stems of woody plants commonly 
increase in girth by the formation of an annual ring of new wood 
beneath their bark, so that the age of stem or branch can be told 
by counting the rings seen in a cross cut. The Butcher’s Broom is 
exceptional among British woody plants in not having its wood thus 
arranged in rings, its structure in this respect resembling in miniature 
the stem of a Palm-tree. 
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