X INTR OD UCTION 



is only held to be native in a natural locality to which 

 it has spread by natural means from a natural source ; 

 that is, when it has been disseminated as it would 

 be in a state of absolute nature. The disqualification 

 of an unnatural introducing agent is exemplified in 

 the case of garden flowers introduced by gardeners from 

 distant lands, and surviving after the garden has reverted 

 to a natural state. The source is, and the habitat appears 

 to be, natural, but the agent is artificial. The dis- 

 qualifying nature of an unnatural source of introduction, 

 even when the introducing agent is natural, is well 

 shown by the same exotic garden flowers when their 

 seeds are dispersed by the wind or by birds into 

 the natural vegetation of the neighbourhood. In the 

 first examples the alien character of the species would 

 be readily recognised in consequence of geographical 

 considerations. It will be seen, however, that, in a 

 majority of cases, the agency and the source of intro- 

 duction must remain unknown. It is upon the remain- 

 ing cause of disqualification, viz., unnatural habitat, 

 that botanists must chiefly rely to distinguish the true 

 alien, for it is the only one which can be easily examined 

 in the field. 



It has not been overlooked that A. de Candolle ex- 

 pended much labour and skill in bringing historical, 

 philological, and physiological evidence to bear upon 

 the status of critical species, and his great work on the 

 subject has been largely consulted, but it is neverthe- 

 less upon the present condition of each species that 

 botanists must chiefly rely. 



The term aboriginal might probably be substituted 

 for "native" in nearly all cases, for the natural agencies 

 which can transfer seeds from natural habitats abroad 

 to those in the British Isles must be very exceptional. 

 It is not, however, so useful a term as "native" or "indi- 

 genous," for it implies a knowledge of the history of 

 species which we seldom possess. If the term "abori- 

 ginal," however, were substituted for "native" in many 

 of our local Floras, expressions such as "native on 



