100 MESSRS. J. А. WHELDON AND W. G. TRAVIS ON 
are as follows :—Lecanora atrynea, Nyl., L. campestris, Nyl., Acarospora 
smaragdula, Koerb., Callopisma erythrellum, Nyl. (very sparingly), C. ferru- 
gineum var. festivum, Nyl. (very sparingly), Lecanora atra, Ach. (in a de- 
pauperate condition), and Verrucaria maura, Wahlenb. (sparingly), the fore- 
going all fruiting. In addition, there are Lecanora parella, Ach. (sterile and 
very badly developed) and what are probably depauperate states of Xanthoria 
parietina, Th. Fr., and Callopisma vitellinum, Sydow. Verrucaria maura is 
the only one of the foregoing which can be called a true maritime species. 
Sand- Dunes.—The range of sand-dunes which fringes the coast between 
the estuaries of the Mersey and Ribble is the most extensive tract of dunes 
in the British Isles, and is noted for its interesting plants. 
The variety and attractiveness of the vegetation have led us to devote much 
attention to these dunes. Furthermore, on account of the situation and the 
nature of the habitat, the lichens on the dunes appear to be comparatively 
little affected by town-smoke. At first sight, the lichen-flora of these sand- 
hills might appear to be a very limited one; in reality, however, it is much 
richer and more varied than would be suspected, and, on investigation, it has 
yielded numerous rare, and even some new, species. The number of species 
of lichens occurring on the dunes to our knowledge is 39. Several other 
species which have been collected in dune localities, on substrata, such as old 
leather and decaying logs, are not included in this estimate, as they are 
probably more correctly regarded as, in a sense, adventive. 
Lichens only form a very subordinate element of dune vegetation; but 
they do play a part, even if a minor one, in the fixing of the sand by vege- 
tation. From an ecological aspect their mode of occurrence and distribution 
on the dunes are of interest. As a rule, lichens are amongst the earliest 
colonisers of bare surfaces, where the substratum is firm, such as rock, soil, 
or bark, and, as is well known, they help to prepare the way for the growth 
of mosses and flowering plants. In а dunal environment, however, such 
lichens as occur are largely dependent on higher plants for the creation of 
certain edaphic conditions requisite for their development and existence. The 
primary condition is that some degree of surface-fixation, produced by the 
growth of vegetation, must have taken place ; and, secondly, for most species 
of dune-lichens some amount of humus seems necessary. In the sand-hills 
of the South Lancashire coast there are two environmental extremes which 
inhibit liehen-growth. These are represented, on the one hand, by growing 
or mobile dunes, the surface of which has not yet become fixed by vegetation 
and is mobile under wind action ; and, on the other hand, by certain types of 
dune-marsh, locally called “ slacks,” which exist in parts of the sand-hills 
where the water-table is close to the surface. In the former case, it is 
mainly want of fixity of surface which impedes lichen development; in the 
latter case, there are no lichens which can develop on ground where standing- 
water, even if shallow, is usually present and deposition of sediment is taking 
