The Present Flora of Britain. 15 
species, or the transfer to other widely separated localities 
of species already in Britain. Marsh plants, of all the 
groups, are the least likely to be introduced accidentally 
or on purpose by man. 
Many of the heath or barren-land plants might be 
classed equally well as marsh species, for gravelly or 
sandy areas tend to become peaty and waterlogged in 
our climate. The most marked characteristic of this flora 
is the occurrence in it of certain gregarious plants, which 
occupy definite areas in enormous profusion, though 
entirely absent from others equally suitable. Several of 
our heaths, for instance, are very local, though all of them 
occur abundantly where found at all. The British plants 
which have a marked western geographical distribution 
within the Islands nearly all belong to the marsh and 
heath groups. 
Of the other open-land groups, that belonging to good 
soil and clayey meadows is surprisingly restricted, and 
many of the species are probably late introductions. It 
is not difficult to see the reason why we have so few 
species characteristic of our wide areas of clayey pasture. 
These, till recent times, were woodland, not open prairie, 
and since the destruction of the woods they have been 
under cultivation or closely grazed. We have therefore 
nothing equivalent to the prairie vegetation of North 
America or other drier climates. Several plants confined 
to the eastern counties belong, however, to this group; for 
there the dry cutting winds of winter probably always 
prevented the forest growth from extending to the sea, 
even where the soil was richest. The other meadow 
species have generally a wide range throughout Britain, 
wherever the climate is suitable. 
Our woodland plants are extremely difficult to deal 
with, partly on account of the wholesale destruction of the 
