1899 } VEGETATION OF TROPICAL AMERICA 7 
forest is much smaller than the area of campos. The relative 
number of species is about 1600 belonging to the forest, and 800 
to the campos. The forest also is much richer in families and 
genera. Of the 149 families of vascular plants living on the 
whole area no less than thirty-seven are peculiar to the forest, 
while but two are peculiar to the campos, and, moreover, each 
of those two is represented by but one species. Further, of all 
the genera (about 750) 364 are to be found only in the forest, 
while only eighty-two are peculiar to the campos. 
Here, again, we meet the question, why this difference? In 
this case I suppose physical conditions to be the causes, although 
historical facts possibly may be of importance. To be able to 
understand this evolution of species it is necessary to know 
whether the campos flora was the primeval one on the old 
Brazilian highland; or whether from the first the forest covered 
the country and, later on, forced by physical alterations, retired 
from the higher and drier parts of the country, where the campos 
arose, beginning with forest species that adapted themselves to 
the new conditions. About this, however, I am not able to say 
anything; we only know that for endless times there must have 
existed open and woodless land in the interior of Brazil, seeing 
that Lund has found here remains of now extinct species of the 
horse and llama types; that is, remains of animals that could 
only live in a woodless country. I myself feel inclined to sup- 
pose that the forest vegetation is the primary one, and for that 
reason also the richest, while the campos vegetation is the 
younger one; for most likely the moisture of the climate was 
much greater when only the inner highland was above the sea, 
and as the country grew larger in every direction the climate 
, gradually grew drier and drier. 
Between the forest and the campos vegetation there seems to 
have been, in a physical way, originally but one difference, namely, 
the unequal moisture in the soil. For the soil in which the two 
different vegetations live is in origin and composition evidently 
all one, namely, the before mentioned red clay, a product of the 
decomposition of the primeval rock. But in the valleys, where 
