underground bulb, green foliage-leaves and coloured floral leaves are
borne on one and the same axis. Generally, flowers are formed only
on shoots of a higher order, often only on the ultimate branches of
a much branched system. A potential branch or bud, either foliage or
flower, is formed in the axil of each leaf; sometimes more than one
bud arises, as for instance in the walnut, where two or three stand in
vertical series above each leaf. Many of the buds remain dormant, or
are called to development under exceptional circumstances, such as
the destruction of existing branches. For instance, the clipping of
a hedge or the lopping of a tree will cause to develop numerous buds
which may have been dormant for years. Leaf-buds occasionally arise
from the roots, when they are called adventitious; this occurs in many
fruit trees, poplars, elms and others. For instance, the young shoots
seen springing from the ground around an elm are not seedlings but
root-shoots. Frequently, as in many Dicotyledons, the primary root,
the original root of the seedling, persists throughout the life of
the plant, forming, as often in biennials, a thickened tap-root, as
in carrot, or in perennials, a much-branched root system. In many
Dicotyledons and most Monocotyledons, the primary root soon perishes,
and its place is taken by adventitious roots developed from the stem.


_Flower._

The most characteristic feature of the Angiosperm is the flower, which
shows remarkable variety in form and elaboration, and supplies the
most trustworthy characters for the distinction of the series and
families or natural orders, into which the group is divided. The
flower is a shoot (stem bearing leaves) which has a special form
associated with the special function of ensuring the fertilization of