Fig. 70), of most
annuals, and of many perennials, serve only for absorption: these are
slender or thread-like. Fine roots of this kind, and the fine branches
which most roots send out are called ROOTLETS.

72. The whole surface of a root absorbs moisture from the soil while
fresh and new; and the newer roots and rootlets are, the more freely do
they imbibe. Accordingly, as long as the plant grows above ground, and
expands fresh foliage, from which moisture largely escapes into the air,
so long it continues to extend and multiply its roots in the soil
beneath, renewing and increasing the fresh surface for absorbing
moisture, in proportion to the demand from above. And when growth ceases
above ground, and the leaves die and fall, or no longer act, then the
roots generally stop growing, and their soft and tender tips harden.
From this period, therefore, until growth begins anew the next spring,
is the best time for transplanting; especially for trees and shrubs.

73. The absorbing surface of young roots is much increased by the
formation, near their tips, of ROOT-HAIRS (Fig. 81, 82), which are
delicate tubular outgrowths from the surface, through the delicate walls
of which moisture is promptly imbibed.

[Illustration: Fig. 83-85. Forms of tap-root.]

74. =Fleshy Roots= are those in which the root becomes a storehouse of
nourishment. Typical roots of this kind are those of such biennials as
the turnip and carrot; in which the food created in the first season's
vegetation is accumulated, to be expended the next season in a vigorous
growth and a rapid development of flowers, fruit, and seed. By the time
the seed is matured the exhausted root dies, and with it the whole
plant.

75. Fleshy roots may be single or multiple. The single root of the
commoner biennials is the primary root, or tap-root, which begins to
thicken in the seedling. Names are given to its shapes, such as

_Conical_, when it thickens most at the crown, or where it joins the
stem, and tapers regularly downwards to a point, as in the Parsnip and
Carrot (Fig. 84);

_Turnip-shaped_ or _napiform_, when greatly thickened above, but
abruptly becoming slender below; as the Turnip (Fig. 83); and

_Spindle-shaped_, or _Fusiform_, when thickest in the middle and
tapering to both ends; as the common Radish (Fig. 85).

76. These examples are of primary roots. It will be seen that turnips,
carrots, and the like, are not pure root throughout; for the caulicle,