GEOGRAPHICAL DISTRIBUTION 141 
the distribution of plants over the surface of the globe. 
The first groundwork necessarily is the preparation of 
floras , i.e. accurate lists of the various species of plants 
growing in the different regions to be dealt with. At the 
same time the exact boundaries of the distribution of the 
various species must be determined, and the same for the 
genera and the natural orders. Given these preliminary 
facts we may then go on to deal with such questions as the 
following. Why is the flora of a given country composed of 
certain species and no others ? How did these species get 
into the country, from what place, and at what time ? Did 
they originate in the country where they are now found, or 
somewhere else, and if so where? Into what associations 
are the plants of a given flora grouped, and what is the 
cause of their grouping ? What is the general physiognomy 
and ecology of these groups ? Why is the flora of Europe 
different from that of similar areas in North America or 
elsewhere? Why is any given species, genus, or family 
confined to a certain area and not found elsewhere, though 
the conditions of life be favourable ? Why is the area 
occupied by a species (or genus or family) usually con- 
tinuous, but frequently disjointed or broken up into separate 
areas? Why are there so many species or genera which 
occur solely in one spot, most often one island or one 
mountain chain (such a species or genus is termed e?idemic), 
and why are such areas characterised by the possession of 
endemic forms ? Why do certain species occur only on the 
various mountain-ranges (e.g. on the Alps, Pyrenees, and 
Carpathians) and not in the intervening lowlands? Why 
are some species common to Europe and New Zealand? 
Such questions and many others require solution ; it is 
evident that to deal properly with them we require an 
extended knowledge of the general ecology of the plants, as 
well as of their phylogeny. At the same time, the study of 
geographical botany throws light on these subjects in turn. 
Distribution of Species, Genera, &c., and limita « 
tion of Area. A species probably arises in a certain 
limited area of the earth’s surface, and spreads from this 
point by aid of the seed- dispersal methods and by veget- 
ative reproduction. We can see this process of spreading 
actually going on in the case of such plants as Lespeaeza, 
