DISTRIBUTION, OF PLANTS — 23 
only those continental species which are best adapted for 
holding their own in a variable climate are found. 
Influence The forms of life in a country or district are 
ofMan. nowhere stationary. At the present time, as in 
the past, there are migrations of plants, the disappearance of 
some species, the gradual development of others ; but these 
changes take place so slowly, if Nature is left to herself, that 
they are almost unnoticed. For centuries, however, the dis- 
tribution of life, both animal and vegetable, has been consider- 
ably modified by the action of man. Animals are introduced 
Into an island and the flora changes, as has been the case in 
St. Helena owing to the introduction of goats. Or certain 
wild animals are exterminated, and this leads to the rapid in- 
crease of certain others—e.q., field-mice—which had formerly 
been kept down, and they in their turn may destroy so much 
vegetation as materially to affect the district. It has been 
shown, for instance, that the abundance of red clover in a 
district will depend on’a good supply of cats—and that cer- 
tainly depends on man—to kill the mice which would otherwise 
destroy and keep down the humble-bees, and thus prevent the 
pollinating of the clover. The action of man in clearing 
forests, in draining swamps, in cultivating waste ground, in 
fact in all the operations of agriculture, has an enormous in- 
fluence on the vegetation of a country. The clearing of 
forests means the lessening the amount of rain, and as the 
majority of plants need a regular rainfall, this often becomes 
a serious matter ; the effect of draining is disastrous to marsh- 
loving plants, as may be seen in Cambridgeshire, for, with the 
exception of Wicken Fen, the Fen District may be said to 
have disappeared. 
British The chief British Floras as given in Keid’s 
Floras. << (Qrigin of the British Flora” are : . 
(1) A Lowland Flora, similar to the temperate flora of the 
neighbouring lowlands of Belgium and France. 
(2) An Upland Flora, consisting of more or less isolated 
portions of the flora of the arctic regions and the Scandinavian 
mountains. This flora is confined to hills high enough to have 
: 
: 
a 
