450 NATURALIZED PLANTS OF GREAT BRITAIN. {JunS, 



which some of the doubtful points have been treated in the ' Geo- 

 graphie Botanique/ 



A plant is here defined to be thoroughly naturalized when it is 

 found, with every appearance of a native, growing and repro- 

 ducing itself regularly without the assistance of man; it must 

 also be proved acclimatized by having survived for a period of 

 years embracing all the varieties of temperature. Such a plant 

 is to be carefully distinguished from those species which obtain 

 only a precarious footing upon the soil (usually near to houses 

 and cultivation), and disappear in the course of a few years unless 

 kept up by repeated importations of seeds : these latter are termed 

 " adventitious," and are liable to be cut off by a severe season. 



The weeds of cultivated land are not considered naturalized, 

 since the greater part of them would disappear if the ground 

 were left untilled. On the other hand, many of the plants which 

 are peculiar to waste places, about houses, walls, ruins, and 

 rubbish-heaps, might continue to find azotized stations suitable 

 for their growth even if the human race were removed. Some of 

 both classes however may have had originally wild stations inde- 

 pendent of human influence ; the tillage-weeds, on broken ground 

 along river-banks or on the seacoast ; the others, near the dens 

 and in the haunts of wild animals. 



A species is not entitled to be called naturalized if when once 

 planted it spreads by means of its roots only, without producing 

 seed;"^ this is the naturalization of an individual, not of a 

 species. 



Three kinds of proof are employed by De Candolle to ascertain 

 whether a plant be native or otherwise. 



1. First the old Floras are consulted to see if they mention the 

 species at all, and in what manner, whether as an undoubted 

 native in their time or not. Another kind of historical evidence 

 is derived from a knowledge of the invasions or migrations of 

 different races of mankind, and of their comaiercial intercourse 

 Avith one another. 



2. The names in popular usage are next examined, to inquire if 

 the plant in question had a name in the older language of the 

 country in which it is now found. 



3. The botanical proofs relate to the nature of the habitat, 

 whether it is in the vicinity of houses, cultivation, or sea-ports ; 



* But is not Anacharis Alsinastrum an instance of this ? ^ 



