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All such plants, when left to struggle for existence with other 
plants, unaided by the interference of mankind, are apt to be 
crushed out of the situations formely occupied by them : and they 
thereby are shown to have been unable in the first instance 
to have spread as unaided colonists into the sites now tenanted 
by them. 
The fact of wide diffusion of any plant in a given locality is not 
in itself sufficient to allow us to infer therefrom its native origin, 
or rather its having arrived in that locality at a distant period 
unaided by man: for some species are so well fitted to survive in 
the struggle that in a few years they establish themselves, and 
may oust the original occupants. This is peculiarly the case 
where the conditions in a locality have been changed by man by 
deforesting or by cultivation, and where plants accustomed to- 
these conditions elsewhere are accidentally, or intentionally 
introduced by him. In such cases the immigrants may in a few 
years spread so widely and become so abundant that they would 
be readily regarded as native to the locality, were we not able 
frequently, through fortunate circumstances, to trace their past 
histories and migrations. Examples of such immigrants in our 
own neighbourhood are Mimulus luteus, Veronica Buxbaumit, 
Aigopodium Podagraria. Lupinus perennis, and grasses employed 
in agriculture, eg., several of the Sevrafalcus group of Bromus,. 
and Lolium italicum. 
Another source of serious uncertainty in determining the claims: 
of not a few species to rank among our indigenous plants arises 
in the facts that in the middle ages plants of Southern Britain or of 
other lands were frequently cultivated, especially in the gardens. 
attached to the religious establishments, because of their real or 
supposed medicinal virtues or as pot herbs ; and that a large pro 
portion of them were discarded at a later period in favour of species- 
of greater value or beauty from distant lands. On thus falling” 
into disrepute, the fact that they had once been cultivated was. 
after a time forgotten, and their extraneous origin fell out of view 
in the case of such as had succeeded in naturalising themselves. 
Probably the species introduced in this way are more numerous- 
than we are aware of. 
But even in the case of species in whose introduction man had 
no part, direct or indirect, the claim to be regarded as indigenous. 
depends largely on the length of time they have been in the 
