FLORAL REGLONS 
i93 
the latter, as we have seen, are correlated with the climatal 
conditions, whilst the composition of the flora is often quite 
different in regions of similar climate and soil. Thus we are 
able to divide the earth’s surface into a number of floral 
regions , taking no account of ecological characters but only 
of the relationships of the plants. It is evident from what 
has been said that a floral region will be characterised by 
the possession of endemic forms ; the greater the number of 
these and the higher their systematic rank the more natural 
is the region. Most of the natural orders have a very exten- 
sive distribution, and occur in many of the floral regions; 
the possession of many endemic genera, tribes, and sub- 
orders, more or less closely allied, is regarded as sufficient 
to mark a floral region. The various regions graduate into 
one another at their edges, and isolated districts belonging to 
one region often occur in the midst of another (e.g. on the 
mountains). The different regions form three chief divisions, 
the bo 7 'eal or northern extra-tropical, the tropical , and the 
austral or southern extra-tropical. The number and extent 
of the floral regions of the globe are differently estimated by 
different writers ; we shall follow here the arrangement given 
by Drude in his Atlas der Pflanzenverbreitung (see Map, 
Frontispiece). Space will only permit of an enumeration of 
the regions, with their chief characters (abridged from Drude). 
Each is again subdivided into domains. 
1. Boreal Group. 1. The Northern Floral Region 
corresponds very closely to the first and second zones of 
vegetation described above. The general systematic features 
of the flora resemble those of the British flora. There are 
forests of Coniferae (Pinus, Picea, Abies, Larix, &c.), 
Fagaceae (Fagus, Quercus), and Betulaceae (Betula) ; other 
common trees and shrubs are species of Acer, Salix, Tilia, 
Fraxinus, Lonicera, Ilex, Elaeagnus, Crataegus, Prunus, 
Pyrus, Sambucus, &c. Many Ericaceae, Caryophyllaceae, 
Ranunculaceae, Compositae, Leguminosae (Papilionatae), 
Cyperaceae, Gramineae, &c. occur abundantly. 
2. The Central Asiatic Region includes Turkestan, 
Mongolia, and Thibet. The district is very dry in summer, 
and there is much salt in the soil in many parts. Trees are 
very rare. Halophytes, e.g. many Chenopodiaceae, are 
numerous ; other characteristic forms are shrubby species of 
w. 
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