[Illustration: FIG. 82.--CRUCIFIXION THORN] The desert tortoise is perhaps the most remarkable of all the animals of the desert. It is rare, and little is known of its habits except that it lives in the most arid valleys of southeastern California, far removed from any water. This tortoise has a diameter across its shell of at least eighteen inches. Its flesh is much prized by the Indians and prospectors. A specimen which had been without water for an indefinite period was dissected, and the discovery was made that upon each side there was a membranous sac, containing clear water, perhaps a pint in all. The desert tortoise, then, carries his store of water with him, and is thus enabled to go many months without a new supply. [Illustration: FIG. 83.--THE GILA MONSTER] A trip across the deserts of the lower Colorado in spring, before the bracing air of winter has entirely gone, is one never to be forgotten. The poisonous insects and reptiles are not at this time warmed up to full activity, while many peculiar plants are just coming into bloom. Let us study some of the strange forms growing thickly over the rocky slopes and sandy plains. There are miles of forest, but not such a forest as we are accustomed to see. Tall, fluted columns of the giant cactus (saguaro), with rows of sharp spines, reach upward to a height of from twenty to fifty feet. At one or more nodes, bud-like branches spring from the main trunk and, curving upward, form columns about the parent stem. [Illustration: FIG. 84.--THE PALO VERDE TREE AND SAGUARO] The giant cactus bears near the top a purple flower and a large, edible fruit. This fruit, which has a red pulp, is a favorite food with the Indians, and also with many insects and birds. It is gathered by means of long forked sticks, for if it should drop to the ground it would be broken. The pulp of the stalk yields a little juice or sap which is used by the Indians when hard pressed for water. [Illustration: FIG. 85.--A FOREST ON THE PLAINS OF SOUTHERN ARIZONA Showing cholla and saguaro] Scattered among the huge club-shaped columns of the saguaro is the cholla, the next largest of the cactuses. This species, which is tree-like in its branching and in rare cases grows to a height of twelve feet, bears bright red or yellow flowers. One must approach with care, for its jointed stems are so easily broken that at the slightest touch of the hand or clothing, pieces break off and adhere firmly by means of their sharp curved and barbed spines. Another species of the cholla is small, reaching but a foot or two above the ground, but this and other low forms so cover the ground in places that one has to be constantly on guard to keep from running the spines into his feet.