148 ABOUT MOSSES AND LICHENS. [CHAP. 
seemed to be Peltigera malacea, but it was not in 
fruit, and a few of the commoner forms of Lecanora 
and Lecidea. Gibside Woods, barring the atmo- 
sphere, are favourable enough for the growth of fruc- 
ticulose and foliaceous lichens, but for any of these 
forms I searched in vain. Not a trace of the series 
Ramolodei could I find. The trees were as barren - 
of Usnea, Ramatlina, and Evernia as if they had 
never known them, and I might say of almost every 
other form. I found here and there on an old fir a 
few barren patches of the thallus of some Calcium ; 
and I noticed a few forms of Lecanora and Lecidea 
by the river side. 
“The lichens which flourished here in the fine con- 
dition spoken of by Winch have perished, and this 
evidently from the pollution of the atmosphere by 
the smoke and fumes from the Tyneside, and the 
collieries of the surrounding district. Though these 
are a considerable distance from Gibside, yet the 
deleterious elements travel on the wind, for the trees 
have that dusky coating on their trunks and branches 
which is peculiar to trees bordering a town, and which 
is fatal to lichen-growth.” * 
The development of these plants is exceedingly 
slow, and they take years to come to maturity, owing 
greatly to the fact that their growth is suspended 
during dry weather. There is little necessity to de- 
scribe them, as all are acquainted with their grey or 
yellow incrustations on the rocks of the mountain 
side, the trunks of trees, and even upon brick walls. 
But beneath this sober coat of grey they possess a 
* Science Gossip, 1879, p. 217. 
