THE ROOT
“The stalk or trunk is the upward-growing part of the plant, and needs
air and light. The root, on the contrary, is the downward-growing part,
and it needs soil and darkness. The extreme ends of the root’s various
subdivisions are always growing, always young, of delicate structure,
and for that reason admirably fitted for imbibing, very much as a fine
sponge would do, the liquids with which the soil is impregnated.
Because of their facility in absorbing moisture these ever-growing
tip-ends are called spongioles. The spongioles terminate the rootlets,
that is to say the final subdivisions of the root, subdivisions known
as root-hairs on account of their resemblance to real hair.
“The root takes various forms, which are all reducible to two
fundamental types. Sometimes it consists of a main body or tap-root,
which sends out branches as it bores deeper into the soil. This
designation, tap-root, is a common and familiar term. Sometimes the
root assumes the form of a tuft, a bunch of rootlets, simple or
branching, which, springing from the same point, continue to grow at a
nearly equal rate and on an equal footing as to importance. Roots of
this sort are commonly known as fibrous roots.
“As a general rule, the growth of the root keeps pace with that of the
stem or trunk. Thus the oak, elm, maple, beech, and all our large trees
have a vigorous, deep-growing root as anchorage for the enormous
superstructure, to brace it firmly against the wind. But there is no
lack of lowly herbage that has roots quite out of proportion to the
other parts,—veritable tap-roots of greater size and vigor than many a
plant of far greater aërial development can boast. To this class belong
the mallow, carrot, and radish. Lucerne has for support to its meager
foliage a root that bores two or three meters into the ground.
“An agricultural practice of supreme interest is based, at least
partly, on the excessive development of certain roots. The plant is a
laboratory where life converts into nutritive matter the manure from
our stables and poultry-yards. A cart-load of dung becomes at the
farmer’s pleasure, after passing through one sort of plant or another,
a crop of peas or beans, a basket of fruit, or a loaf of bread. Hence
this fertilizer is a very precious thing which nothing can replace and
which must be utilized to the very utmost. The nourishment of us all
depends on it. Enriched with this fertilizer, the soil produces, we
will say, a first harvest of wheat. But wheat with its bunch of short
and fine roots, has drawn only upon the upper layer of fertilizing
material, leaving intact all that the rain has dissolved and carried
down into the lower layers. It has performed its mission admirably, it
is true; it has made a clean sweep and converted into wheat all the
fertilizer contained in the layer of soil accessible to its roots, so
that if wheat were sown a second time no harvest would be obtained. The
soil, then, is exhausted on the surface, but in its underlying strata
it is still rich. Well, what crop shall we choose for the utilization
of these lower strata and the production of still further supplies of
food? It cannot be barley, oats, or rye, since their little fibrous
roots would find nothing to glean in the surface soil after the first
crop of wheat. But it will be lucerne, since this plant will send down
its roots, each as thick as your finger, to the depth of one, two, or
even three meters, if need be, and give back the fertilizer in the form
of forage, which, with the help of the animal that feeds on it, will be
converted into nutritious meat, valuable dairy products, excellent
wool, or, at the very least, animal power for draft service or other
work. This succession of two or more different kinds of crops for the
utmost utilization of a given area of prepared soil is called rotation
of crops, of which there will be more to say later.
“Deep roots, so admirably adapted to the utilization of the lower
strata of the soil, become in other circumstances a source of serious
difficulty. Suppose a tree is to be transplanted. Its long tap-root
will make the operation difficult and hazardous. You must dig deep,
both in pulling it out and in replanting it; and then you must be
careful not to injure the root, for it is all in one piece and if it
does not take hold and grow the sapling will die. In this case it would
be much to the tree’s advantage to have fibrous roots running down only
to a slight depth; it could then be pulled up easily, and if some roots
perished in the operation enough would be left intact to insure the
success of the transplanting.
“This result can be obtained: it is no difficult matter to make the
tree lose its tap-root and acquire, not a regular bundle of roots of
even length; but a short and much ramified root that possesses the
advantages of the bunch of small roots without having its shape. Thus
in nurseries where young trees remain for some years before being
transplanted, after two years’ growth a spade is passed under the
surface of the soil to cut off the main root, which would in time
become a deep tap-root. The stump that remains then branches out
horizontally without going deeper. Another way is to pave the nursery
bed with tiles. The tap-root of the young tree pushes downward until it
reaches this barrier, where it is straightway forced to stop growing in
depth and compelled to send out lateral branches.
“The kind of root we have thus far been talking about is primordial,
original; every plant has it on emerging from the seed; it appears as
soon as the seed germinates. But many plants have other roots that
develop at different points of the stem, replacing the original root
when that dies, or at least coming to its aid if it continues to live.
They are called adventitious roots, and they play a highly important
part, notably in certain horticultural operations such as propagating
by slips and layers, which we will talk about later.
“Besides these two operations, the object of which is to multiply the
plant, it is customary to prompt the growth of adventitious roots
either for the purpose of fixing the plant more firmly in the ground or
in order to increase its yield. The best way to attain this result is
to bank up the earth at the base of the stalk. This process is
sometimes called earthing up. The buried portion soon sends out a great
number of roots. Indian corn, for example, if left to itself is too
poorly rooted to resist wind and rain, which beat it down. In order to
give it greater stability the farmer earths up the corn. In the earth
banked up at the base of the stalk bundles of adventitious roots form
and furnish the plant a firmer support.
“Wheat stalks bear on their lower ends buds which, according to
circumstances, perish to the detriment of the harvest or develop into
roots and promote the growth of more ears of grain. Let us suppose
wheat has been sown in the autumn. In that cold and rainy season
vegetation is slow, the stalk grows but little, and the various buds
remain very close together almost on a level with the ground. But if
they are favored by having damp soil near them, these buds send forth
adventitious roots which nourish them directly and promote a fullness
of growth that the ordinary root by itself could not have secured. Thus
stimulated by nourishment, these buds develop into so many
wheat-stalks, each one ending at a later period in an ear of grain. But
if wheat is sown in the spring, its rapid growth under the influence of
mild weather brings the buds too high for them to send out roots. The
stalk then remains single. In the first case from one grain of wheat
sown there springs a cluster of stalks producing as many ears; in the
second case the harvest is reduced to its lowest terms: from one grain
of wheat one stalk, one ear. Hence this development of the lower buds
of cereals is of the greatest importance. To obtain it, or, in
agricultural terms, to make the wheat send up suckers, the lower buds
must send down adventitious roots, as they will do if they are brought
into contact with the soil. To this end, shortly after germination a
wooden roller is passed over the field, and this roller, without
bruising the young stalks, pushes them deeper into the ground.”