branous 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.

These are not all the plants of this wonderful forest. The ocatilla
is a cactus-like form having a group of long slender stems bunched
together at the root. In the spring each is tipped with a spike of
red flowers, and as the snake-like stalks wave in the breeze