Page:Popular Science Monthly Volume 61.djvu/496

490 The seeds of the cholla, like those of several allied species, rarely if ever germinate on the open mesa. In eight years of observation in its center of distribution I never found a seedling of this plant growing wild. It spreads almost entirely by vegetal dissemination, i. e., by the ends of the branches becoming detached and transported often long distances from the mother plant.

The cholla is perfectly adapted not only for the easy detachment of the ends of the branches, but for their wide dissemination as well. The fruit which hangs from the tree in long, pendulous clusters as illustrated in Fig. 6 is within easy reach of cattle and other large animals.

These clusters of succulent fruits are without spines and are for the most part sterile. The fruit from the standpoint of seed production is of very little service to the plant in aiding in its perpetuation and dissemination. Its chief service appears to be to entice animals to the plant that the fragile ends of the branches which become detached at the slightest disturbance may adhere to them and become scattered far and wide.

In order that these fruits may best serve their purpose they are succulent, unarmed and as eagerly eaten by animals when green as when ripe. Moreover they often remain on the plant for two or more years if undisturbed. During periods of scanty forage in the region where the cholla grows it is not an uncommon sight to see the range cattle with their heads literally covered with these formidable cactus burs