Thickened barks.
Gathering moisture.
Many of the shrubs and trees like the sangre de dragon and the torote have enlarged or thickened barks to hold and supply water. If you cut them the sap runs readily. When it congeals it forms a gum which heals over the wound and once more prevents evaporation. Existence for the plants would be impossible without such inventions. Plant life of every kind requires some moisture all the time. It is an error to suppose because they grow in the so-called “rainless desert” that therefore they exist without water. They gather and husband it during wet periods for use during dry periods, and in doing so they seem to display almost as much intelligence as a squirrel or an ant does in storing food for winter consumption.
Attacks upon desert plants.
Browsing animals.
Is Nature’s task completed then when she has provided the plants with reservoirs of water and tap roots to pump for them? By no means. How long would a tank of moisture exist in the desert if unprotected from the desert animals? The mule-deer lives here, and he can go for weeks without water, but he will take it every day if he can get it. And the coyote can run the hills indefinitely with little or no moisture; but he will eat a water melon, rind and all, and with great relish, when the opportunity offers. The sahuaro, the bisnaga, the cholla, and the pan-cake lobed prickly pear would have a short life and not a merry one if they were left to the mercy of the desert prowler. As it is they are sometimes sadly worried about their roots by rabbits and in their lobes by the deer. It seems almost incredible but is not the less a fact, that deer and desert cattle will eat the cholla—fruit, stem, and trunk—though it bristles with spines that will draw blood from the human hand at the slightest touch.
Weapons of defense.
The spine and thorn.
Nature knows very well that the attack will come and so she provides her plants with various different defenses. The most common weapon which she gives them is the spine or thorn. Almost everything that grows has it and its different forms are many. They are all of them sharp as a needle and some of them have saw-edges that rip anything with which they come in contact. The grasses, and those plants akin to them like the yucca and the maguey, are often both saw-edged and spine-pointed. All the cacti have thorns, some straight, some barbed like a harpoon, some curved like a hook. There are chollas that have a sheath covering the thorn—a scabbard to the sword—and when anything pushes against it the sheath is left sticking in the wound. The different forms of the bisnaga are little more than vegetable porcupines. They bristle with quills or have hook-shaped thorns that catch and hold the intruder. The sahuaro has not so many spines, but they are so arranged that you can hardly strike the cylinder without striking the thorns.
The crucifixion thorn.