NORTHUMBEELAND AND DURHAM. 109 



verifying the nomenclature of the Flora. Circumstances which 

 we need not enter upon here have caused it to be broken into 

 two halves and divided between the Museum at Newcastle and 

 the Linnean Society in London. The collections of Eobertson 

 and an interleaved copy of the Guide of 1805, with copious anno- 

 tations, are in the ]S"ewcastle Museum. The collection of the 

 late Wm. Backhouse, of Darlington, was unfortunately consigned 

 to the hands of Mr. Baker for use in the preparation of this work 

 when his herbarium and library were totally destroyed by fire in 

 1864 and perished in the conflagration, as did also a large num- 

 ber of plants gathered by the late Mr. John Storey, which were 

 the property of the Blyth Mechanics' Institute. Besides these, 

 we have been indebted to the Eev. W. W. JSTewbould for compar- 

 ing our Catalogue, after it was written out, with the herbarium 

 of Professor Oliver, now the property of University College, 

 London. 



Classes of CithensMp. — A point which requires to be carefully 

 attended to in enumerating the plants of any particular district, 

 is to draw a line of distinction as clearly as circumstances will 

 allow between those which really belong to it as aboriginal inhab- 

 itants and those which owe their introduction to human inter- 

 vention. In any long-settled, long-cultivated tract of country, 

 the modification which has been brought about by human agency 

 is, of necessity, very considerable. Around the place where man 

 fixes his dwelling swamps, moors, and woods disappear to make 

 way for cultivated fields, roads, and gardens : the bog, heath, 

 and shade-loving plants are restricted in their range or altogether 

 exterminated ; and the places which these occupied are filled up 

 by the species which man grows for food or other purposes and 

 the weeds which these bring in their train. Out of the eleven 

 hundred and thirty-seven enumerated in the following list, we 

 can only claim with confidence eight hundred and forty-four as 

 genuine natives. But a considerable proportion of the introduc- 

 tions are now very thoroughly settled down. Following the 

 nomenclature of the Cylele Britannica we have called the well- 

 established agricultural weeds by the name of Colonists, and the 



