THE LICHENS OF SOUTH LANCASHIRE. 97 
South Lancashire.* Ecologically, too, the lichen-flora of the limestone is of 
interest by reason of its different facies from that of our siliceous rocks and 
soils. So far as our district is concerned, comparatively few species seem 
common to both types of substratum. With the calcareous rocks is associated 
the presence of numerous species, belonging more especially to the Colle- 
maces and Verrucariaceæ, which are absent from our siliceous rocks. We 
have endeavoured, therefore, in our Systematic List to point out those 
species which show a decided preference for either of these two types of 
rock or soil. We have also attempted to record, so far as observed, some 
of the subtler degrees of selectivity evinced by many species of lichens in 
regard to the nature of their habitat. This selectivity may be illustrated by 
the lichens of our Carboniferous Limestone. For example, certain strongly 
xerophytie species seem absolutely restricted to surfaces of bare rock where 
there is а minimum of moisture and of organic matter, and where they are 
exposed to a maximum of light and air. Thus on outcrops of bare limestone 
rock, as on the summit of Worsaw Hill, the following species occur :— 
Collena jurvum, Ach., Pannularia nigra, Nyl., Squamaria sawicola, Poll., 
Placodium murorum, DC., P. tegularis, Ehrb., Lecanora irrubata, Nyl., 
L. galactina, Ach., L. campestris, Nyl., Aspicilia gibbosa, Koerb., A. calcarea, 
Somm., Acarospora pruinosa, Jatta, Lecidea immersa, Ach., Verrucaria 
nigrescens, Pers, V. mauroides, Schaer., V. maculiformis, Krempelh., 
V. rupestris, Schrad., V. calciseda, DC., and Acrocordia epipolwa, A. L. Sm. 
The black patches of Pannulariu nigra, Nyl., and Verrucaria nigrescens, 
Pers., and the orange-coloured crusts of Placodium murorum, DC., are con- 
spicuous to the eye on the white rock; but it is only under a lens that the 
numerous less obtrusive species are visible, and the whole surface of the rock 
is seen to be spotted with the black fruits of the Verrucarie, which often pit 
therock. An analogous habitat is afforded by the limestone walls, and many 
of the foregoing lichens, as well as others, are common on the stones, the 
following being noticeable :—-Хап она parietina, Th. Fr., Placodium 
murorum, DC., P. tegularis, Ehrb., /’hyscia tenella, Nyl., P. stellaris 
var. leptalea, Nyl., Xanthoria lychnea, Th. Fr. (rare), Lecanora irrubata, 
Nyl., L. galactina, Ach., Callopisma erythrellum, Nyl., Aspicilia calcarea, 
Somm., Acarospora pruinosa, Jatta, Buellia canescens, De Not., Verrucaria 
nigrescens, Pers., Ke. 
On the other hand, certain species, e. g. Leproloma lanuginosa, Nyl., 
Urceolaria seruposa, Ach., Gyalecta cupularis, Schaer., Biatorina lenticularis, 
Koerb., Opegrapha saxicola, Ach., Verrucaria papillosa, Ach., and V. Dufourii, 
* Several species which are frequent on the Carboniferous Limestone elsewhere in the 
North-West of England have not yet been found with us, e. g. Leptogium lacerum, Gray, 
L. pulvinatum, Nyl., Solorina saccata, Ach., Squamaria crassa, Huds., Placodium elegans, 
DC., P. candicans, Nyl., Leproplaca xantholyta, Nyl, and Dermatocarpon miniatum, 
Th. Fr. 
