root hairs, here large enough to be seen by the naked
eye. 82. Lower end of this root, magnified, the root seen just as
root-hairs are beginning to form a little behind the tip.]

67. =Secondary Roots= are those which arise from other parts of the
stem. Any part of the stem may produce them, but they most readily come
from the nodes. As a general rule they naturally spring, or may be made
to spring, from almost any young stem, when placed in favorable
circumstances,--that is, when placed in the soil, or otherwise supplied
with moisture and screened from the light. For the special tendency of
the root is to avoid the light, seek moisture, and therefore to bury
itself in the soil. _Propagation by division_, which is so common and so
very important in cultivation, depends upon the proclivity of stems to
strike root. Stems or branches which remain under ground give out roots
as freely as roots themselves give off branches. Stems which creep on
the ground most commonly root at the joints; so will most branches when
bent to the ground, as in propagation by _layering_; and propagation by
_cuttings_ equally depends upon the tendency of the cut end of a shoot
to produce roots. Thus, a piece of a plant which has stem and leaves,
either developed or in the bud, may be made to produce roots, and so
become an independent plant.

68. =Contrast between Stem and Root.= Stems are ascending axes; roots
are descending axes. Stems grow by the successive development of
internodes (13), one after another, each leaf-bearing at its summit (or
node); so that it is of the essential nature of a stem to bear leaves.
Roots bear no leaves, are not distinguishable into nodes and internodes,
but grow on continuously from the lower end. They commonly branch
freely, but not from any fixed points nor in definite order.

69. Although roots generally do not give rise to stems, and therefore do
not propagate the plant, exceptions are not uncommon. For as stems may
produce adventitious buds, so also may roots. The roots of the Sweet
Potato among herbs, and of the Osage Orange among trees freely produce
adventitious buds, developing into leafy shoots; and so these plants are
propagated by _root-cuttings_. But most growths of subterranean origin
which pass for roots are forms of stems, the common Potato for example.

70. Roots of ordinary kinds and uses may be roughly classed into
_fibrous_ and _fleshy_.

71. =Fibrous Roots=, such as those of Indian Corn (