hillocks, near the coast undergo a complete change. As if by a stroke of magic blooming vegetation overspreads the ground, which is covered with pasture and wild flowers, chiefly compositæ and crucifers. But this only lasts for a short time. Generally the deserts present a desolate aspect, with no sign of vegetation or of a living creature. In the very loftiest regions of the air the majestic condor may perhaps be seen floating lazily, the only appearance of life.
Imagine the traveller, who has wearily toiled over many leagues of this wild and forbidding region, suddenly reaching the verge of one of the river valleys. The change is magical. He sees at his feet a broad expanse covered with perpetual verdure. Rows and clumps of palms and rows of willows show the lines of the watercourses. All round are fruit gardens, fields of maize and cotton, while woods of algaroba fringe the valley and form one of its special features.
The algaroba (Prosopis horrida) is a prickly tree rarely exceeding forty feet in height, with rugged bark and bipinnate foliage. The trunks never grow straight, soon become fairly thick, and as their roots take little hold of the friable earth, they fall over into a reclining posture, and immediately begin to send off new roots in every part of the trunk in contact with the soil. They thus assume a twisted and fantastic appearance, more like gigantic corkscrews than trees. The algaroba has racemes of small yellowish green flowers which nourish multitudes of small flies and beetles, and they in their turn supply food to flocks
