wing
spring or summer. Annuals are fibrous-rooted.

85. =Biennials=, of which the Turnip, Beet, and Carrot are familiar
examples, grow the first season without blossoming, usually thicken
their roots, laying up in them a stock of nourishment, are quiescent
during the winter, but shoot vigorously, blossom, and seed the next
spring or summer, mainly at the expense of the food stored up, and then
die completely. Annuals and biennials flower only once; hence they have
been called _Monocarpic_ (that is, once-fruiting) plants.

86. =Perennials= live and blossom year after year. A perennial herb, in
a temperate or cooler climate, usually dies down to the ground at the
end of the season's growth. But subterranean portions of stem, charged
with buds, survive to renew the development. Shrubs and trees are of
course perennial; even the stems and branches above ground live on and
grow year after year.

87. There are all gradations between annuals and biennials, and between
these and perennials, as also between herbs and shrubs; and the
distinction between shrubs and trees is quite arbitrary. There are
perennial herbs and even shrubs of warm climates which are annuals when
raised in a climate which has a winter,--being destroyed by frost. The
Castor-oil plant is an example. There are perennial herbs of which only
small portions survive, as off-shoots, or, in the Potato, as tubers,
etc.

Section VI. STEMS.

88. =The Stem= is the axis of the plant, the part which bears all the
other organs. Branches are secondary stems, that is, stems growing out
of stems. The stem at the very beginning produces roots, in most plants
a single root from the base of the embryo-stem, or caulicle. As this
root becomes a _descending axis_, so the stem, which grows in the
opposite direction is called the _ascending axis_. Rising out of the
soil, the stem bears leaves; and leaf-bearing is the particular
characteristic of the stem. But there are forms of stems that remain
underground, or make a part of their growth there. These do not bear
leaves, in the common sense; yet they bear rudiments of leaves, or what
answers to leaves, although not in the form of foliage. The so-called
stemless or _acaulescent_ plants are those which bear no obvious stem
(_caulis_) above ground, but only flower-stalks, and the like.

89. =Stems above ground=, through differences in duration, texture, and
size, form herbs, shrubs, trees, etc., or in other terms are