1G4 Analysis of' Scientific Books and Memoirs. 



science. Shortly after, 1817, appeared his essay " sur les iignes isother- 

 ?nes," which reduced the knowledge of the distribution of heat on the 

 globe into a system, and as it also contains botanico-geographic mate- 

 rials, it is an invaluable work to the planto-geographer. At the same 

 time Decandolle published some interesting information on the planto- 

 geography of France, and on the knowledge of the influence of height 

 on vegetation, in the " Mtmoires de la Societi d'Arcueilj" and in the 

 following year, It. Brown, on the Herbarium of Professor Smith, gave 

 a view of the vegetation in the vicinity of the Congo, like that on New 

 Holland, with particular regard to the distribution of the families of 

 plants. There are here also ample inquiries with respect to the species 

 which occur in several far separated countries. With similar views re- 

 garding Denmark and Guinea has Professor Hornemann enriched the 

 science; and von liuch has made us acquainted with the Flora of the 

 Canary Isles in a planto-geographic point of view. Lastly, Decandolle in 

 the " Dictionnaire des Sciences JYaiurelles," has published the view of the 

 science already spoken of. 



To prevent misapprehension, and to obtain a nearly similar degree of 

 difference throughout the Floras in general, I think it most proper to fix 

 certain rules concerning what is requisite to form a Flora, or what I would 

 rather call a Phyto-geograjJtic region. I am therefore of opinion, that we 

 should require for this, (l.) That at least half of the species should be 

 peculiar : (2.) That at least a quarter of the genera should be proper to 

 the region, or at least have there so decided a maximum, that their species 

 in other regions might merely be considered as representatives : (3.) 

 That individual families of plants be either peculiar to the region, or else 

 have there their maxima. Nevertheless, where this last property is want- 

 ing, while the difference in genera and species is very considerable, we might 

 admit of a region. 



The regions may, again, according to a minor degree of difference in the 

 vegetation, be divided into provinces, for which, for example, one fourth 

 of peculiar species, and a few peculiar genera, might be sufficient. 



In order to have a complete view of the phy to-geographic divisions of the 

 globe, the boundaries and circuit of each, its climatic and other physical 

 relations, should be described ; there should, besides, be mentioned what 

 are the characteristic families and genera which prevail, and that both in 

 regard to species in general, and individuals ; and lastly, a view should be 

 given of the whole habit and character of the vegetation. Towards this, 

 the following is merely a loose sketch. The regions and provinces are best 

 named after the vegetable forms which characterize them, (for the pre- 

 vailing vegetable forms are very often the same in different countries.) I 

 have here attempted this ; at the same time, however, I have added the 

 commonly used geographical terms, * and adopted these last only in cases 

 when I thought that a certain division of the earth ought to form a dis- 

 tinct region, but knew not the vegetation intimately enough to determine 

 the characteristic forms. 



• Wildenow, Decandolle and Treviranus have used only the latter. 



