GAINS TO THE FLORA 145 
suitable habitats by the destruction of the native 
vegetation which occupied them, and this has resulted 
in a general advance of a large number of species. 
What renders the study of this advance so difficult is 
the fact that on all disturbed land the truly native 
plants which have been ousted are striving side by 
side with the immigrants to regain their former terri- 
tories; and it is now often very difficult to disentangle 
them: to separate the sheep from the goats. If.only 
we could have had a Watson’s “Topographical 
Botany” written five thousand years ago, before our 
restless race began to mess up the vegetation! 
However, as has been said, what we have lost on 
one side we have gained on another. On every side 
bright immigrants meet the eye. Our old buildings 
and quarries often blaze with the Red Valerian 
(Kentranthus ruber) and Wallflower (Cheiranthus 
Cheiri); in fields Poppies of various kinds, Corn 
Cockle (Lychnis Githago), and Corn Blue-bottle 
(Centaurea Cyanus) add a glory to the rich green or 
gold of the cereals; dry banks and gravelly places are 
decorated with species of Melilot (Melilotus), Chamo- 
mile (Anthemis), Knapweed (Centaurea), and many 
others. The flora of harbours and docksides is often 
as cosmopolitan as the sailors of the ships by whose 
agency it came there; and the unfamiliar weeds—the 
gipsies and tramps of the plant world—which we 
encounter on roadsides, rubbish-heaps, and railway 
stations lend an additional interest to our botanical 
rambles. 
Turning now to the plants which are used by man, 
it may be pointed out in the first place that the human 
race obtains much more, whether of profit or of 
Io 
