4 
b 
432 Structural and Physiological | Botany. - 
’ 
a 
{ 
Cupuliferze, Ericaceze, Myrtaceze, Melastomacee, Lauraceze, 
Composite, Umbelliferee | Labiate, Cruciferee, Primulaceze], 
Cactacez, arborescent Euphorbiaceze, [Mesembryanthe- ~ 
macez|, [figs], Malvaceze, Mimosez, and Nympheacee. 
CHAPTER VIII. 
BOTANICAL GEOGRAPHY. 
BoTANICAL GEOGRAPHY treats of the distribution of plants 
on the surface of the earth ; it collects the plants of any par- 
ticular country into a Flora, and investigates the causes, 
operating either at the present time or in the past, which 
have led to each species acquiring its special habitat, and 
have resulted in only a few plants—termed cosmopolitan — 
becoming distributed over the whole globe, or even over a 
large part of it.! 
The earth does not everywhere produce those plants which are 
especially adapted to each particular region. If this had been the case, — 
the same species would be constantly met with in widely separated 
countries that enjoy a similar climate, and no immigration of foreign 
plants would take place, such as often happens before our eyes. Each 
species has, in fact, become disseminated only at particular spots ; it has 
its centre of distribution at the spot from whence it originally sprang ; 
‘but the limits of these centres are often obscure, because plants have 
found conditions suitable for their existence outside these bounds, and 
feebly represented by our grape-vine, ivy, hop, honeysuckle, [Convol- 
vulus], &c. 
1 The phyto-geographical map at the end of the volume must be 
consulted in connection with this chapter. It indicates the boundaries 
of the twenty-four phyto-geographical regions adopted by Grisebach in 
his ‘ Vegetation der Erde,’ each region being coloured uniformly. The 
regions of a more generally wooded character are coloured green and 
dark blue, the steppes and deserts yellow and red, while those regions — 
which have no special character of their own are of some other colour. 
[The statements of Grisebach—on whose work the whole of this chapter _ i 
is founded—are somewhat too unqualified, both with regard to the boun- — 4 
daries between the regions and to the characters which distinguish nee 
from one another,— ED. ] 
