Commit a seed to the earth; plant, for example, a Lima bean, at the
depth of two inches in moist vegetable soil. The seed will not be
slow to germinate; first swelling, and then bursting its outer skin,
a vegetable in miniature will, after a time, slowly reveal itself
to the observer. In the meantime two very distinct parts make their
appearance; one, yellowish in color, already throwing out slender
fibrous shoots, sinks farther into the soil,--this is the _radicle_, or
root; the other of a pale greenish color, takes the opposite direction,
ascends to the surface, and rises above the ground,--this is the stem.
This root and stem are the essential organs of vegetation, without
which, when we have excepted certain vegetables of an inferior order,
plants adorned with leaves and flowers cannot exist. How vast the
difference between the verdant top of a tree, which rises graceful
and elegant into mid-air,--not to speak of the flower it bears--and
the coarse, tangled mass of its roots and rootlets, without harmony,
without symmetry! These organs, so little favored in their appearance,
have, however, very important functions in the order of vegetable
action.
The chief offices of the root are two: in the first place, it attaches
the plant to the soil, holds it in its place, and prevents it from
being overwhelmed by the elements. In the second, it feeds the plant by
absorbing from the earth the sap necessary to its growth. How is this
done?
The root branches again and again as it grows, throwing out numerous
smaller branches. These hollow, thread-like rootlets suck up, from the
soil, the water and other things, which are to go, through the stem or
trunk and the branches, to all the leaves. Here these are made into the
perfect sap, which, being distributed, causes the plant to grow, to
blossom, and to bear fruit.
The manner in which roots succeed in overcoming obstacles, has always
been a subject of surprise to the observer. The roots of trees and
shrubs, when cramped or hindered in their progress, have been observed
to exhibit considerable mechanical force, throwing down walls or
splitting rocks; in other cases, clinging together in bunches, or
spreading out their fibres over a prodigious space, in order to follow
the course of a rivulet with its friendly moisture.
A celebrated botanist of the last century relates that, wishing to
preserve a field of rich soil from the roots of a row of elms, which
would soon have exhausted it, he had a ditch dug between the field
and the trees in order to cut the roots off from it. But he saw with
surprise that those roots, which had not been severed in the operation,
had made their way down the slope so as to avoid meeting the light, had
passed under the ditch, and were again spreading themselves over the
field.
There are some roots which are developed along the stem itself.
These supplementary organs come as helps to the roots properly so
called, and replace them when by any cause they have been destroyed.
In the primrose, for example, both the principal and the secondary
roots springing from it, perish after some years of growth, but the
supplementary roots, springing from the lower part of the stalk,
prevent the plant from dying.
In the tropical forests of America and Asia, the vanilla, whose fruit
is so sought after for its sweet aroma, twines its slender stem round
the neighboring trees, forming an elegant, flexible, and aerial
garland, an ornament in these vast solitudes, at once grateful and
pleasing. The underground roots of the vanilla would not be sufficient
for the nutriment of the plant, and the rising of the nourishing sap
would take place too slowly. But Nature makes up for this inconvenience
by the air roots which the plant throws out at intervals along its
stem. Living in the warm and humid atmosphere of tropical forests,
the stronger shoots soon reach the ground and root themselves in the
soil. Others float freely in the atmosphere, inhaling the moisture and
conveying it to the parent stem.
A grand tree--the banyan, or the pagoda fig-tree--adorns the landscape
of India, and presents the most remarkable development of aerial
roots. When the parent stem has attained the height of some fifty
or sixty feet, it throws out side branches in every direction, and
each branch in its turn throws out supplementary roots, which descend
perpendicularly in long slender shoots till they reach the ground.
When they have rooted themselves in the soil, they increase rapidly in
diameter, and soon form around the parent stem thousands of columns,
each throwing out new lateral branches and new roots.
“The bended twigs take root, and daughters grow
About the mother tree, a pillared shade.”
The natives love to build their temples in the intervals left between
these roots of the wild fig-tree. A famous banyan tree on the Nerbuddah
is said by Professor Forbes to have three hundred large and three
thousand smaller aerial roots; it is capable of sheltering thousands of
men, and thus forms one of the marvels of the vegetable world; it is,
in short, a forest within a forest.
Roots constantly endeavor to bury themselves in the earth. They seem to
shun the light of day; and this tendency is to be seen from the very
first moment when the root shows itself in the seed. The tendency is so
decided, and appears so inherent in the life of all vegetables, that
if we reverse a germinating seed, placing it with the root upwards,
the root and the stem will twist round of themselves,--the stem will
stretch upward, and the root will bury itself in the ground.