Again, when studying plants for the purpose of identification, it is often important to note whether the root is _annual_, _biennial_, or _perennial_; that is, whether the root lives for one season only, lives throughout the winter, and supports the plant for a second season, or retains its life for an indefinite number of years.
Most of the roots that live over one season are of a fleshy nature, thick and tapering, or tuberous, and contain more or less stored nourishment which assists the new growths that are called forth by the warmth and light of the early spring sun.
The stems of plants exhibit a much greater variety of structure and habit than do the roots. Their chief functions are to support the leaves and flowers, and to arrange these parts in such a manner that they obtain the maximum of light and air; also to form a means of communication by which the sap may pass in either direction. Stems also frequently help to protect the plant, either by the development of thorns or prickles, or by producing hairs which prevent snails and slugs from reaching and devouring the leaves and flowers.
The character of the stem is often of some importance in determining the species, so we must now note the principal features that should receive our attention.
As regards surface, the stem may be _smooth_ or _hairy_. In general form, as seen in transverse section, it may be _round_, _flattened_, _triangular_, _square_, or traversed longitudinally by ridges and furrows more or less distinct. Flattened stems are sometimes more or less _winged_ with leaf-like extensions, as in the Everlasting Pea, in which case the wings perform the functions of foliage leaves. It should also be noted whether the stems are _herbaceous_, or _woody_, and whether they are _hollow_, or _jointed_.
In some plants the stem is so short that the leaves appear to start direct from the root, as in the Dandelion and Primrose. Such stems are said to be _inconspicuous_.
[Illustration: RUNNING UNDERGROUND STEM OF SOLOMON'S SEAL
_a_, Terminal bud from which the next year's stem is developed; _b_, Stem of the present year; _c_, and _d_, Scars of the stems of previous years.]
The longer and conspicuous stems are either _simple_ or _branched_, and they may be _erect_, _prostrate_, _trailing_, _climbing_, or _running_. In the case of climbing stems it should be noted whether the necessary support is obtained by means of tendrils, rootlets, or suckers, or by the twining of the stem itself.