the spring drought, and it grows abundantly until it forms the
wonderful stretches of waving green where the buffalo once grew
fat. Moreover the fine glacial soil of the prairies is so clayey
and compact that the roots of trees cannot easily penetrate it.
Since grasses send their roots only into the more friable upper
layers of soil, they possess another great advantage over the
trees.

Far to the south of the prairies lie the grass-lands of tropical
America, of which the Banos of the Orinoco furnish a good
example. Almost everywhere their plumed grasses have been left to
grow undisturbed by the plough, and even grazing animals are
scarce. These extremely flat plains are flooded for months in the
rainy season from May to October and are parched in the dry
season that follows. As trees cannot endure such extremes,
grasses are the prevailing growth. Elsewhere the nature of the
soil causes many other grassy tracts to be scattered among the
tropical jungle and forest. Trees are at a disadvantage both in
porous, sandy soils, where the water drains away too rapidly, and
in clayey soil, where it is held so long that the ground is
saturated for weeks or months at a time. South of the tropical
portion of South America the vast pampas of Argentina closely
resemble the North American prairies and the drier plains to the
west of them. Grain in the east and cattle in the west are fast
causing the disappearance of those great tussocks of tufted
grasses eight or nine feet high which hold among grasses a
position analogous to that of the Big Trees of California among
trees of lower growth.

It is often said that America has no real deserts. This is true