nical species,
but included at the beginning of the 20th century the largest area of
virgin forest on the surface of the earth. The flora falls naturally
into three great divisions: that of the Amazon basin where exceptional
conditions of heat and moisture prevail; that of the coast where heat,
varying rainfall, oceanic influences and changing seasons have greatly
modified the general character of the vegetation; and that of the
elevated interior, or _sertao_, where dryer conditions, rocky
surfaces, higher sun temperatures and large open spaces produce a
vegetation widely different from those of the other two regions.
Besides these, the flora of the Paraguay basin varies widely from that
of the inland plateau, and that of the Brazilian Guiana region is
essentially distinct from the Amazon. The latter region is densely
forested from the Atlantic to the Andes, but with a varying width of
about 200 m. on the coast to about 900 m. between the Bolivian and
Venezuelan _llanos_, and thus far civilization has made only a very
slight impression upon it. Even where settlements have been located,
constant effort is required to keep the vegetation down. Along the
coast, much of the virgin forest has been cut away, not only for the
creation of cultivated plantations, but to meet the commercial demand
for Brazil-wood and furniture woods.

The chief characteristic of the Amazonian forest, aside from its
magnitude, is the great diversity of genera and species. In the
northern temperate zone we find forests of a single species, others of
three or four species; in this great tropical forest the habit of
growth is solitary and an acre of ground will contain hundreds of
species--palms, myrtles, acacias, mimosas, cecropias, euphorbias,
malvaceas, laurels, cedrellas, bignonias, bombaceas, apocyneas,
malpigias, lecythises, swartzias, &c. The vegetation of the lower
river-margins, which are periodically flooded, differs in some
particulars from that of the higher ground, and the same variation is
to be found between the forests of the upper and lower Amazon, and
between the Amazon and its principal tributaries. The density of the
forest is greatly augmented by the _cipos_, or lianas, which overgrow
the largest trees to their tops, and by a profusion of epiphytes which
cover the highest branches. As a rule the trees of the Amazon forest
are not conspicuously high, a few spe