There are other growths that seem to have a fine sense of discretion in the matter of danger, for they let fall all their leaves at the first approach of drouth. The ocatilla, or “candle wood” as it is sometimes called, puts out a long row of bright leaves along its stems after a rain, but as soon as drouth comes it sheds them hastily and then stands for months in the sunlight—a bundle of bare sticks soaked with a resin that will burn with fire, but will not evaporate with heat. The sangre de dragon (sometimes called sangre en grado) does the same thing.
Tap roots.
Underground structure.
But Nature’s most common device for the protection and preservation of her desert brood is to supply them with wonderful facilities for finding and sapping what moisture there is, and conserving it in tanks and reservoirs. The roots of the greasewood and the mesquite are almost as powerful as the arms of an octopus, and they are frequently three times the length of the bush or tree they support. They will bore their way through rotten granite to find a damp ledge almost as easily as a diamond drill; and they will pry rocks from their foundations as readily as the wistaria wrenches the ornamental wood-work from the roof of a porch. They are always thirsty and they are always running here and there in the search for moisture. A vertical section of their underground structure revealed by the cutting away of a river bank or wash is usually a great surprise. One marvels at the great network of roots required to support such a very little growth above ground.
Feeding the top growth.
Yet this network serves a double purpose. It not only finds and gathers what moisture there is but stores it in its roots, feeding the top growth with it economically, not wastefully. It has no notion of sending too much moisture up to the sunlight and the air. Cut a twig and it will often appear very dry; cut a root and you will find it moist.
Storage reservoirs below ground.
The storage reservoir below ground is not an unusual method of supplying water to the plant. Many of the desert growths have it. Perhaps the most notable example of it is the wild gourd. This is little more than an enormous tap root that spreads out turnip-shaped and is in size often as large around as a man’s body. It holds water in its pulpy tissue for months at a time, and while almost everything above ground is parched and dying the vines and leaves of the gourd, fed from the reservoir below, will go on growing and the flowers continue blooming with the most unruffled serenity. In the Sonora deserts there is a cactus or a bush (its name I have never heard) growing from a root that looks almost like a hornet’s nest. This root is half-wood, half-vegetable, and is again a water reservoir like the root of the gourd.
Reservoirs above ground.
But there are reservoirs above ground quite as interesting as those below. The tall fluted column of the sahuaro, sometimes fifty feet high, is little more than an upright cistern for holding moisture. Its support within is a series of sticks arranged in cylindrical form and held together by some fibre, some tissue, and a great deal of saturated pulp. Drive a stick into it after a rain and it will run sap almost like the maguey from which the Indians distill mescal. All the cacti conserve water in their lobes or columns or at the base near the ground. So too the Spanish bayonets, the yuccas, the prickly pears and the chollas.