ALIEN PLANTS 143 
directly or indirectly, to human activities. We may 
compare these figures with those drawn from a study 
of the flora of Kent, which faces across the Channel 
towards France just as county Dublin faces across the 
Irish Sea towards England; both are areas of early 
settlement and both lie in the main stream of traffic. 
In Kent we have to deal with a larger area (1,570 
square miles), and a larger flora (1,160 species). We 
find that, of these 1,160 species, 146, or about one- 
eighth, are set down as owing their presence to man.* 
And so it is in all the more populous and highly tilled 
parts of our islands. 
This question of alien plants, their past history and 
present standing, is one of the most puzzling with 
which the student of our flora has to deal. In the 
first place, most of them have been in the country for 
a long time, and the record of their introduction is 
lost. Next, while many of them are confined to 
ground disturbed by man, and thus clearly exist under 
man’s protection—however unwillingly that protec- 
tion may be afforded—others have mixed with the 
indigenous flora, won a place in the closed native 
vegetation, and might be ranked as true natives were 
it not that a study of their general distribution raises 
doubts as to the possibility of their having arrived in 
our islands unaided—doubts which their known 
occurrence in gardens tends to confirm. Take the 
case of the Yellow Monkey-flower (Mimulus Langs- 
dorfi). This has quite established itself in our native 
flora, in some places ascending mountain streams far 
into the hills, in others mingling with the rank flora of 
* F, J. Hanspury and E. S. Marsuatt: ‘‘ Flora of Kent,’’ 1899, 
Pp. XXXv. 
