A HISTORY OF DURHAM 



LICHENS {Lichenes) 



The lichen-flora of a given district under changing conditions 

 furnishes evidence to the observant mind that it does not nourish its 

 life as other plants do. If it did so we should naturally expect that 

 the lichens would hold their own with their fellows, subject, of 

 course, to the ordinary changes which come alike to all vegetable 

 forms. But it is not so. The lichen will disappear from a spot, 

 and more especially the frondose or foliaceous forms, without any 

 observable change in the other vegetation around it, and that from 

 a pollution of the atmosphere which is not sufficient to affect those 

 plants which nourish themselves from the soil or matrix of growth. 

 I had an opportunity of giving an illustrative case of this kind from 

 the county of Durham,' where lichens spoken of by Mr. Winch as 

 flourishing in Gibside Woods many years before had utterly perished 

 — killed by the fumes from the Tyneside some miles away. 



It is fortunate, therefore, that the lichen-flora of Durham county 

 was fairly well worked before the large development of its present 

 coal and iron industries. Nearly 200 species and varieties of lichens 

 are recorded in Winch's Flora of Northumberland a?id Durham as having 

 been gathered in the county. I also catalogued in 1887, in the 

 Natural History Society s 'Transactions, Northumberland and Durham, Mr. 

 Winch's lichens in the museum, Newcastle-on-Tyne ; but this was 

 only a partial list, as a number of his lichens with other of his 

 herbaria are in the possession of the Linnean Society. 



As a county, Durham had and still possesses an extensive lichen- 

 growth. The physical features of the country are various and 

 favourable. Its eastern seaboard, of course, is poor in results, but its 

 sub-alpine elevations westward and north-west are good. Limited in 

 its outcrop of rock, the limestone predominates in its highest parts 

 crossed and broken by the basalt. The best lichen districts in the 

 county are the river valleys of the Derwent, the Tees, and the 

 Wear. The last two, with elevations margining the upper reaches of 

 the valleys, and the fells enclosing the river sources, are excellent 

 hunting grounds for the botanist generally as well as the lichenologist ; 

 and these districts are the least affected by any deleterious atmospheric 

 elements carried by the wind. 



The previous workers in this humble branch of botanical science 

 in Durham were Nathaniel John Winch," Mr. Robertson, and the 

 Rev. John Harriman, of Egglestone, Teesdale. By his careful 

 observations and exertions, Mr. Harriman contributed largely to the 

 knowledge and extension of our northern lichenology. He discovered 

 a number of new species. One of these, Urceolaria diacapsis, Ach., 

 he found near Barnard Castle. A micro-diagnosis of this beautiful 



'Science Goiii/>, 1879. 



* He was a native of Newcastle, a zealous student of nature, and a distinguished botanist ; well 

 known in the north of England hy the Rot/tnlst'i Guitie to Northumberland and Durham and his Flora of the 

 same counties, published in the Trans/icliom of the Natural History Society, Netvcastle-on-Tyne. 1832. 



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