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.