316 THE REGIONS OF VEGETATION. 
better adapted to the smaller sections of a flora, or region, 
where the prevalence of a tribe is of more importance. 
Schouw considers that in each region one-fourth of the 
genera which belong to it should possess there the chief 
part of their species, and that one half of the species should 
be peculiar ; whilst he also mentions the importance derived. 
from families having their principal stations there. These 
are, however, at best, very arbitrary rules. 
In venturing to advance opinions of my own, I must pre- 
mise that they are founded on convictions, the result of such 
experience as I have had ; and though I am far from main- 
taining that the division of the globe into regions is natural, 
yet, I must admit, that the large continents present several 
very striking changes in their vegetable productions. The 
western coast of the Americas forms a boundary to the Pacific, 
extending north and south for about eight thousand miles. 
With nearly the whole of this I had an opportunity of be- 
coming acquainted, in a voyage prolonged several years, and 
I became strongly convinced of the individuality of the flora 
within certain ranges. But for this, I should, in all proba- 
bility have been content to limit the regtons to the number of 
Professor Schouw. 
There are so many, and such decided differences between 
the large continents, that it my be occasionally sdp to 
retain them as a whole, p their furtherdivision intore- 
gions. Itis unnatural, I own, dos SO, Tur the plan has its con- 
veniences, Seven botanical provinces may be enumerated, the 
European, the Asiatic, the African, the North American, the 
South American, and the Oceanic. The islands in their 
vicinity are considered as forming a part of the province of 
the neighbouring continent, and all the Polynesian islands are 
included in the Australian. These provinces must be re- 
garded rather as convenient assemblages of regions, under 
which the physical conditions of the country, the direction 
and height of the mountain chains, and the general features 
of the climate can be studied ; than as sections of the world, 
erected on natural characters. 
