^74 Baron Humboldt on the Laws whkh are observed 
equator to the pole, follow the same law of decrease, in propor-^ 
tionas they rise toward the summit of the equatorial mountains ? 
Do not the mutual proportions of families vary^ on isothermal 
lines of the same denomination, in the temperate zones^ to the 
north and to the south of the equator? These questions belong 
to the geography of plants^ properly so called: they are connected 
with the most important problems belonging to meteorology and 
the natural history of the globe in general. Upon the prepon- 
derance of certain families of plants, depends also the character 
of the landscape, the aspect of a country, whefcr of a beautiful 
or majestic nature. The abundance of the Gramineag, which 
form vast savannahs, and that of the Palms or the Coniferae, 
are much influenced by the social state of the people, by their 
manners, and by the more or less perfect development of the 
econotnical arts. 
In considering the geographical distribution of forms, we may 
attend to species, to genera, and to natural families, (Humboldt,^ 
Proleg. in Nov. Pen. vol. i. pp. xiii. li, & 33.). Often a^ single 
species of plants, especially among those which I have named 
social plants, covers a vast extent of country. Of this kind, in 
the north, are the heaths and forests of pines ; in equinoctial 
America, the associations of Cactus, Croton, Bafnbusa, and 
Brathys of the same species. It is curious to examine the pro^ 
portions of organic multiplication and development. We may 
demand what species in a given zone produces the greatest 
number of individuals ;-“We may point out the families to which- 
in different climates belong the species which predominates over 
the others. Our imagination is peculiarly struck with the pre- 
ponderance of certain plants, which we consider, on account of 
their easy reproduction, and the great number of individuals 
which present the same specific characters^ as the more common 
plants of this or that zone. In a northern region, where the 
Composites and the Ferns are to the phaenogamous plants in- 
the proportion of 1 : 13, and of 1 : 25, (that is to say, where we' 
find these proportions on dividing the total number of the phm-^ 
nogamous plants by the number of the speeies of the Compo- 
sitae and Ferns,) a single species of Fern may occupy ten times^^ 
as much space as the whole species of Composite together. In 
this case, the Ferns predominate over the Compositge by the' 
