The Social Plants Which Almost Exclusively Predominate In The Steppes, Are Monocotyledons; And It Is Known How Much Grasses Impoverish The Soil Into Which Their Fibrous Roots Penetrate.

This action of the killingias, paspalums and cenchri, which form the turf, is everywhere the same; but where the

Rock is ready to pierce the earth this varies according as it rests on red sandstone, or on compact limestone and gypsum; it varies according as periodical inundations accumulate mud on the lower grounds or as the shock of the waters carries away from the small elevations the little soil that has covered them. Many solitary cultivated spots already exist in the midst of the pastures where running water and tufts of the mauritia palm have been found. These farms, sown with maize, and planted with cassava, will multiply considerably if trees and shrubs be augmented.

The aridity and excessive heat of the mesas do not depend solely on the nature of their surface and the local reverberation of the soil; their climate is modified by the adjacent regions; by the whole of the Llano of which they form a part. In the deserts of Africa or Arabia, in the Llanos of South America, in the vast heaths extending from the extremity of Jutland to the mouth of the Scheldt, the stability of the limits of the desert, the savannahs, and the downs, depends chiefly on their immense extent and the nakedness these plains have acquired from some revolution destructive of the ancient vegetation of our planet. By their extent, their continuity, and their mass they oppose the inroads of cultivation and preserve, like inland gulfs, the stability of their boundaries.

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