Page:Popular Science Monthly Volume 61.djvu/495

Rh It is probable that the thick covering of spines is of some value to the plant in protecting it from the full force of the intensely bright sunlight and also of some value in checking transpiration. These ever present and formidable, barbed spines are well illustrated in Fig. 5. They serve their greatest usefulness to the cholla in preventing its destruction by animals and in the important part which they play in the dissemination of the species. All the younger branches of the cholla are soft and succulent and, were it not for their efficient armor

of barbed spines, would be quickly destroyed by herbivorous animals. In acquiring a condensed and succulent plant body in order to fit itself to a desert environment the cholla would have courted its own ruin were it not that it acquired a full equipment of spines at the same time. From every standpoint it is, as an individual, admirably equipped for its desert home. It is, however, more than this; it is the best equipped of all desert plants for rapid and wide dissemination. It makes ample provision for its offspring.