74 On the Lichen-Flora of Epping Forest , 
And the last cause to he noticed of the diminution of the 
lichen-flora of the Forest is the increase and extension of 
villages in the neighbourhood. It is true that about old 
rural villages and small towns in most parts of the country a 
very fair number of lichens may always be gathered, especially 
of such species as usually occur in cultivated tracts. But 
where building operations on an extensive scale are being 
conducted, and the physical features of the old villages are 
thus entirely altered, and new ones here and there springing 
into existence, a large decrease, if not the total extinction of 
previously existing species necessarily results. And this not 
only from the destruction of old trees, pales, and walls in 
fields and gardens, but also from the alterations produced 
upon the surroundings of the natal site of such lichens as 
remain. For so impatient are they of such alterations which 
prevent free access of air, that the old habitats become no 
longer suitable for their growth, and they languish and decay. 
Hence about Hoe Street, Walthamstow, and Houghton, where 
numerous species were collected by Forster, as also about 
Epping Town, where several were formerly gathered by 
myself, we would at present vainly search for any in a fully- 
developed condition. The paucity of lichen-growth in these 
localities, it may here also be observed, is attributable to the 
atmosphere being in some states of the weather more or less 
impregnated with smoke from the increased number of human 
habitations on the outskirts of the Forest, the acids contained 
in which are most destructive to lichens. Add to this that 
the direction of the prevailing winds being from the S.W., 
the smoke and fogs of London and its suburbs extend their 
deleterious influence at certain seasons of the year to the 
nearer portions of the Forest, and even considerably beyond; 
and we cannot be surprised that the result should be a great 
decrease in the numbers and change upon the condition of 
its lichens. In fact, in so far as I have more recently 
observed, these exist only in leprarioid or imperfect states 
about the villages, the only exception almost being Lecidea 
myriocarpa, which seems better adapted than any other 
species (unless perhaps Lecanora galactina) to withstand the 
influence of smoke. 
