hi the Distrihutw-n Vegetable Porms. ^81 
four systems of vegetation, those of the New Continent, of Wes- 
tern Africa, of India, and of New Holland. Since, notwith- 
standing the regular increase of the mean heat from the pole to 
the equator, the maximum of heat is not identical in the diffe- 
rent regions at different degrees of longitude, there exist also 
places where certain families attain a more perfect development 
than at any other : this is the case with the family of Composi- 
tae in the temperate region of North America, and especially at 
the southern extremity of Africa. These partial accumulations 
determine the physiognomy of the vegetation, and are what we 
call vaguely the characteristic features of the landscape. 
In the whole temperate zone, the Glumaceae and Composite 
form together more than the fourth part of the phaenogamous 
plants. We find, from the same inquiries, that the forms of 
organised beings have a mutual dependence. The unity of 
nature is such, that the forms are universally limited according 
to constant and immutable laws. When we know at any point 
of the globe the number of species which a great family pre- 
sents, (for example, that of the Glumace^, the Compositae, or 
the Leguminosge,) we can estimate with much probability both 
the total number of phasnogamous plants, and the number of 
species which compose the other vegetable families. It is thus, 
that, on knomng the number of Cyperacem or of Compositag in 
the temperate zone, we can form an estimate of that of the 
Graminem or Leguminosse. These estimates enable us to see in 
what tribes of vegetables the Floras of a country are still defi- 
cient : they are so far from being uncertain, as to enable us to 
avoid confounding the quotients which belong to the different 
systems of vegetables. The labour which I have bestowed 
upon plants, will no doubt one day be applied with success to 
the different classes of vertebral animals. In the temperate 
zones, there are nearly five times as many birds as mammalia, 
and the latter increase much less toward the equator than the 
birds and reptiles. 
The geography of plants may be considered as a part of the 
natural history of the globe. If the laws which nature has fol- 
lowed in the distribution of vegetable forms, should prove to be 
more complicated than they appear at first sight, still, we ought 
not on this account to be deterred from submitting them to ac- 
