60 INTRODUCTION. 
introduced species from the aboriginal natives of Britain ; because 
those species (if any) which were so introduced, and became 
thoroughly established before botanical history commenced, are 
now unavoidably looked upon as aboriginal natives; while all 
degrees of uncertainty appertain to the other species, whose 
conditions here still show some sort of evidence of a foreign origin. 
Cultivation has been carried on in this island during many 
centuries; while our truly reliable records scarcely extend back 
one century. Really careful observations and reasonings on the 
nativity of species can hardly be dated back half a century. Even 
in the present day, the records made by a large number of the 
locality-reporters are too often unreliable by reason of their 
deficient knowledge, carelessness in observation, inaccuracy of 
language, or wilfully one-sided statements. 
A series of terms, drawn from our own legal and social classi- 
fications, has been used to express the various grades of uncer- 
tainty or belief with respect to those plants whose aboriginal 
nativity is more or less unsettled. The terms ‘ Native, Denizen, 
Colonist, Alien, Casual’ serve to express a descending series, from 
the truly wild and pre-historically established species, down to the 
occasional stragglers from cultivation, or the products of seeds 
accidentally imported with merchandize, ship-ballast, or otherwise. 
The word “naturalised” has been so variously and carelessly 
applied by botanical writers, that it has ceased to carry with 
it any exact signification. It ought to mean a species originally 
introduced by man, but now become thoroughly established, by 
seed or otherwise, among the native plants of the country, and 
existing without human aid in sowing its seeds or in preparing the 
ground for them. We have two American plants fully coming up 
to this definition,— Impatiens julva and Elodea canadensis. Few 
botanists indeed restrict the use of the term “naturalised” to this 
just and proper meaning; while some will even apply it to mere 
casuals, stragglers from cultivation, with no permanent or certain 
locality. 
The Natives, Denizens, and Colonists will be formally treated 
in this volume. The Aliens and Casuals will be enumerated in 
