IV. EXPLANATIONS, ETC. 315 



one plant may occur barely above 52, another barely below 53 ; and 

 consequently, the assumed temperature for the line of 53 will be nearer 

 correctness for the one plant than for the other. 



The Provinces within which the species severally have been ascer- 

 tained to occur, or have been found reported on authority deemed 

 reliable, are indicated by their corresponding numerals. On comparing 

 these numbers with those given for the same species, under the head of 

 " Area" in former volumes, it will be seen that the most distrusted pro- 

 vinces are here usually omitted ; some others being also now left out, 

 which were before allowed to pass unchallenged. These omissions are 

 mostly suggested by ihe alleged localities remaining unconfirmed, and 

 being originally liable to distrust. On the contrary, additions have 

 been made in other instances, through increase of knowledge and of 

 records during the years which have elapsed since the former volumes 

 of this work were written. Such variations from time to time become 

 necessary ; since existing knowledge is still highly incomplete, and past 

 records are frequently discovered to be in part erroneous. 



In too many instances it is hardly better than optional or arbitrary, 

 up to which of the provinces the species are traced in a northerly 

 direction. The actual northward extension of the denizens and colo- 

 nists, — the first province in which they ought to be deemed aliens only, 

 — must often be matter of individual opinion, or even of conjecture only, 

 as before remarked. And the artificial or man- aided extension north- 

 wardly, of the really native species, must frequently make doubtful their 

 true native limits, whether reckoned by provinces or by lines of latitude. 

 Who can certainly say in which province the Viola odorata or Narcissus 

 Pseudo-Narcissus ceases to present a native claim or character ? Who 

 can in like manner now tell where Sainbucus niyra or Ribes rubrum is 

 truly native, and where denizen or alien only ? Casual stragglers aud 

 indubitable introductions, from England into Scotland, are too fre- 

 quently reported as wild natives by the botanists and botanical collectors 

 of the latter country ; and the same errors or falsifications are committed 

 with regard to the native plants of one province, when found in another 

 to which they do not naturally appertain. And thus it happens, that 

 the writer of this work still finds much uncertainty in regard to the pro- 

 vince or the latitude, where several of the plants would most correctly 

 be deemed to cease. 



Under each latitudinal group, the species are enumerated in a series 

 or succession determined by the uos. of the provinces, in connexion with 



