62 



have very little water in the season of drought. 

 These streams scarcely flow at all toward the 

 north ; so that in the centre of the steppes there 

 remains vast tracts of land {bancos and mesas) 

 frightfully parched. The eastern parts, ferti- 

 lized by the Portuguesa, the Masparro, and the 

 Orivante, and by the tributary streams, which 

 are very near each other, of these three rivers, 

 are the most susceptible of cultivation. The 

 soil is sand mixed with clay, covering a bed 

 of quartz pebbles. The vegetable mould, the 

 principal source of the nutrition of plants, is 

 every where extremely thin. It is scarcely aug- 

 mented by the fall of the leaves ; which, though 

 less periodical in the forests of the torrid zone, 

 takes place however, as in temperate climates. 

 During thousands of years the llanos have been 

 destitute of trees and brushwood ; a few scat- 

 tered palms in the savannah add little to that 

 hydruret of carbon, that extractive matter, which 

 (according to the experiments of Saussure, Da- 

 vy, and Braconnot) gives fertility to the soil. 

 The social plants, that almost exclusively pre- 

 dominate in the steppes, are monocotyledons ; 

 and it is known how much grasses impoverish 

 the soil, into which their roots with close fibres 

 penetrate. This action of the killingias, paspa- 

 lums, and cenchri, which form the turf, is 

 every where the same ; but where the rock is 

 ready to pierce the earth, this varies according 



