everywhere in the valleys of Aragua, to the cultivation of indigo;
which, according to the planters, is, of all plants, that which most
exhausts (cansa) the ground. The real physical causes of this
phenomenon would be an interesting inquiry, since, like the effects of
fallowing land, and of a rotation of crops, it is far from being
sufficiently understood. I shall only observe in general, that the
complaints of the increasing sterility of cultivated land become more
frequent between the tropics, in proportion as they are near the
period of their first breaking-up. In a region almost destitute of
herbs, where every plant has a ligneous stem, and tends to raise
itself as a shrub, the virgin soil remains shaded either by great
trees, or by bushes; and under this tufted shade it preserves
everywhere coolness and humidity. However active the vegetation of the
tropics may appear, the number of roots that penetrate into the earth,
is not so great in an uncultivated soil; while the plants are nearer
to each other in lands subjected to cultivation, and covered with
indigo, sugar-canes, or cassava. The trees and shrubs, loaded with
branches and leaves, draw a great part of their nourishment from the
ambient air; and the virgin soil augments its fertility by the
decomposition of the vegetable substances which progressively
accumulate. It is not so in the fields covered with indigo, or other
herbaceous plants; where the rays of the sun penetrate freely into the
earth, and by the accelerated combustion of the hydrurets of carbon
and other acidifiable principles, destroy the germs of fecundity.
These effects strike the imagination of the planters the more
forcibly, as in lands newly inhabited they compare the fertility of a
soil which has been abandoned to itself during thousands of years,
with the produce of ploughed fields. The Spanish colonies on the
continent, and the great islands of Porto-Rico and Cuba, possess
remarkable advantages with respect to the produce of agriculture over