Along the northern line, the visitor should look for the somber, almost black, forest of spruce and fir with its white patches of aspen on the 10,000-foot slopes. Descending farther southward, even a casual observer will note that these species give way first to the yellow pines, then to the junipers (“cedars”) and dwarf pines or piñons. The visitor arriving from the south will find most conspicuous of all the olive-green creosote bush in its summer-winter foliage, next, the omnipresent mesquite (_Prosopis_), then the various _Opuntia_ cacti (chollas and prickly pears), and the yuccas. As he comes in from Arizona, the splendid saguaros will beckon him toward the gateway of New Mexico, but they will nowhere enter it themselves. The vase-shaped body of the ocotillo consisting of unbranching, ten-foot wands should be recognized at a glance, as likewise should the various yuccas and agaves. And in early springtime, a low tree with a rounded mass of golden bloom will joyously proclaim its identity as a paloverde. The desert plants thus enumerated can be recognized along various stretches of U.S. 66 as one holds his speed at a conservative ninety or, even better, at a conservative sixty. The amateur scientist will need to do some homework before he learns much systematic botany or plant physiology. It takes considerable study to comprehend the slow, age-long process which has resulted in the evolution of all this grotesque vegetation: the interaction of extreme aridity, high temperature, low humidity, high evaporation, infrequent precipitation, the hostility of numerous chemical solutions, and the natural rapacity of the animal population. Each plant must have an adaptation of its own, from the tiny winter annual, which must race through its course from a tender rosette to ripened seed before the searing sunshine arrives, on up through the series to the stoic saguaro, which seems able to scorn nature’s enmity.