But some plants produce roots in the air, as in poison ivy and the trumpet creeper, without injury or the gardener’s skill, and are known as aërial roots. They are some of the most peculiar and fantastic of nature’s devices for allowing plants to grow in apparently unfavorable places. In many orchids, some relatives of the pineapple, and a few other air-inhabiting plants, the roots live wholly in the air, the plants being fastened to a tree or even to a telegraph wire. Such plants live on the air and water vapor, and are mostly inhabitants of moist tropical regions.
Quite the most extraordinary of aërial roots are those produced in certain kinds of fig trees. Starting perhaps a hundred feet in the air and no thicker than a lead pencil they appear first as slender vine-like streamers blown hither and yon by the wind. Eventually they reach the ground and penetrate it, grow often to a great size and even form trunklike connections with the tree top. The banyan tree of India is the best known case of this peculiar habit. One which started from a single trunk, subsequently sending out great numbers of aërial roots, has now spread to such a size that it is over 2,000 feet in circumference, has 3,000 trunks, and once sheltered 7,000 soldiers.
A variation of this habit is the case of a giant fig tree of the West Indies in which a bird may deposit the seed of another tree. The seedling soon develops, sending out long, at first threadlike, aërial roots which are wrapped around the tree trunk. As the roots increase in size and further encircle the trunk they ultimately reach the ground, where they are frequently a foot in diameter. Then the true nature of the process becomes evident. For these apparently innocent aërial roots, as they reach the ground, have so completely inclosed the old trunk and their pressure is so great that they literally strangle the tree from which they started. It is slower but just as deadly as the strangulation of an animal by a boa constrictor, for these encircling roots cut off by strangulation the ascent of the sap, thus killing the tree. Fate sometimes overtakes them, however, as it is a common sight to see the strangler meet the same end. Some of nature’s most ruthless battles are fought out in this way, very silently, but very effectively.
THE STEM
