94 MESSRS. J. А. WHELDON AND W. G. TRAVIS ON 
as even strongly to affect lichens which grow on the ground; and the 
Cladonie, such as С. coccifera and C. cervicornis, on some of our moorlands 
are in such a depauperate condition as hardly to be nameable. In our 
upland districts some species of Stereocaulon and Sphwrophorus should be 
present; and if we may judge by the general statements in the * Flora of 
‘'odmorden’ (216), they formerly did occur, but there is now no trace of 
their existence. 
In the coastal piain the number of possible habitats for rupestral lichens 
is greatly curtailed by the rarity of rock outcrops and even stone walls ; but 
it is evident that the condition of saxicole lichens in the greater part of the 
low country is not much better than it is in the hills of “ Kast Lancashire." 
In short, throughout the whole of South Lancashire saxicole lichens, at any 
rate so far as a siliceous substratum is concerned, are, to say the least, very 
seriously affected. We find, exactly аз is the case with corticole lichens, 
that horizontal surfaces, such as the copings of walls, low kerbstones by 
roadsides, the surface of stones partly buried in the ground, and the surface 
of the ground itself, all yield more and better developed specimens than the 
perpendicular or inclined faces of rocks and walls. For example, the finest 
specimens of Parmelia physodes are to be found on bare sand-dunes, some of 
the thalli being several inches in diameter, whilst elsewhere our examples 
are small and stunted. 
It has been pointed out by Wheldon & Wilson (26) that a calcareous 
substratum seems to counteract the effects of smoke on saxicole lichens. 
This is fully borne out by our experience in South Lancashire. We find 
that lichens are far commoner and better developed on limestone and mortar 
than on siliceous rocks. We attribute this to the circumstance that on а 
calcareous substratum the sulphuric acid combines with the lime to form 
sulphate of lime (Ca30,). In this way the acid in the surface-washings is 
largely neutralized, and the chance of the plants receiving it in a concen- 
tration of poisonous potency is reduced to a minimum. The effectiveness of 
this aetion is to be well seen in the outskirts of а great urban district, such 
as on the north side of Liverpool. There we have found the following 
species in good fruiting condition on the mortar of walls, or on cement or 
concrete :— Lecanora urbana, Nyl., L. campestris, Nyl., L. umbrina, Nyl., 
L. crenulata, Nyl., Verrucaria muralis, Ach., V. rupestris, Schrad., var. 
subalbicans, Mudd, Thelidium microcarpum, А. L. Sm., and Staurothele 
hymenogonia, A. Zahlbr. Some of these frequently occur on the mortar of 
sandstone walls quite close to the town, whilst on the surface of the sand- 
stone itself no other lichens are present. The small tract of Carboniferous 
Limestone in the South Lancashire portion of the Ribble Valley is situated 
in a district which enjoys the most favourable conditions of atmospheric 
purity to be found in the vice-county, and for that reason is less available 
tor showing the neutralizing effects oË a calcareous substratum on smoke 
