Ix.] ABOUT MOSSES AND LICHENS. 147 
though in form many of them resemble some of the 
Liverworts. Yet though allied to the Fungz, there 
is no close relation to them. Fungi derive their 
nourishment from the substances upon which they 
grow. Not so Lichens. Their food is absorbed 
from the atmosphere, and it may be taken as a 
general rule that where Lichens grow the atmo- 
sphere is pure, for any impurity kills them. They 
have been observed to disappear entirely from dis- 
tricts where they formerly occurred in great abund- 
ance; and such disappearance has been entirely due 
to the pollution of their atmosphere by the growth 
of a manufacturing town, the establishment of a 
colliery, or other smoke-producing industry. Mr. W. 
Johnson, in a recent volume of “Science Gossip,” 
gives an instance of the disappearance of a species 
from the woods of Gibside, Durham. “In Winch’s 
‘Flora of Northumberland,’ published in the Trans, 
Nat. Hist. Society of Northumberland and Durham, 
1832, mention is made of a number of lichens grow- 
ing in woods at Gibside, Durham. Amongst the 
plants enumerated is Evernia prunastri, said to be 
in fructification in Gibside Woods. As I have never 
had the pleasure of gathering this species in fruit in 
any part of North Durham, or the west and south of 
Northumberland (which I have more or less searched) 
I went out to Gibside in the spring to see if I could 
find the above lichen. Gibside is some seven miles 
from Newcastle to the south-west. The hall is beau- 
tifully placed on the Derwent. The surrounding 
woods run back on to Whickham Fell. On the 
latter I found one or two forms of Cal/ema, and what 
