THE LICHENS OF SOUTH LANCASHIRE. 91 
and this doubtless impedes the development of spores, for many lichens, 
particularly bark-loving species, often exhibit such marked selective 
preferences in regard to the nature of the substratum of thoir habitat, that 
they will only grow on the bark of certain kinds of trees, 
III. PRESENT STATE or THE Licnen-Frora. 
We think that these adverse conditions have now reached their maximum, 
and that a slight improvement has even begun to manifest itself. Increasing 
attention is being paid to the subject of smoke-abatement, and all the 
tendeneies are towards an alleviation of the smoke-nuisance. The ever- 
growing use of gas and electricity for power, light, and heating, means a 
vast saving in coal-consumption, and a consequent reduction in the produc- 
tion of smoke. The adoption of mechanical-stokers and smoke-consuming 
furnaces in our factories, and, still more, the advent of the internal combustion- 
engine as a means of power-production, are big steps in the right direction. 
It is probable that domestic fires are now more responsible for the smoke- 
nuisance than the factory-furnace. It may be pointed out, however, that even 
if improved methods of coal-consumption were to effect the nearly total 
abolition of smoke aad soot, yet so long as coal is burnt at all, the production 
of sulphuric acid in the atmosphere is inevitable. All hepe of improvement, 
therefore, lies in a diminution of the amount of coal consumed and the 
substitution of coal by other kinds of fuel. Any change in this respect is 
likely to be a slow one, particularly as regards domestic fires. It is probable, 
then, that a long time will elapse before the smoke-nuisance is totally 
abolished in a county like Lancashire ; but with evidence on every hand 
pointing to an alleviation of the evil in the future, we may confidently look 
forward to improved conditions: and that this improvement will continue, 
and even progress with greater rapidity as time goes on, is practically certain. 
To every improvement in the degree of atmospheric impurity the lichen- 
flora will respond step by step, until normal conditions are re-established. 
With these anticipations of better things before us, we have now to deal 
with the lichens of South Lancashire as they are at present. Our paper will 
serve to depict the lichen-flora as it appeared when at its worst, and our 
Systematic List may be useful some day to compare with a regenerated flora, 
which will assuredly develop when the air becomes purer. With this in 
mind, our object is to draw as faithful a picture as we can of the present 
state of the lichen-flora, and to describe the peculiar conditions under which 
it now exists. This is necessary, since, without some explanation, the list 
which fellows might be liable to mislead in several ways. It would hardly 
be comprehensible to lichenologists of the future working at a regenerated 
flora, and incapable of realizing the conditions which obtain at present.’ The 
absence of records of many common species might be attributed to our 
H2 
