THE LICHEN PAMXLT. 



513 



very sparingly and infrequently. The structure of the apothecia 

 is only to be learned with the aid of a microscope. It is indis- 

 pensable to the determination of the genera, though the species may 

 be discriminated independently of it. Here, nevertheless, as in the 

 case of the mosses, and for the same reason, I do not attempt to give 

 descriptive characters, or to do anything more than enumerate the 

 species occurring in our neighbourhood, amounting, as nearly as I can 

 ascertain, to seventy-three, or about a fifth of the entire number 

 indigenous to Great Britain, which, according to Smith's English 

 Flora, is four hundred. The comparative fewness of the Manchester 

 species is referable to the flatness of our surface. Many pretty species 

 are to be found on the moors, and in the neighbouring woods and 

 doughs, and in parks and old orchards in Cheshire ; but the majority 



Fig. 229. 



Opegrapha (Letter-lichen), 

 on a piece of bark. 



Fig. 230. 

 Physcia ciliaris. 



of those enumerated are not obtainable nearer than on the high hills 

 beyond Disley, Hamsbottom, Staly bridge, and Rochdale, and even there 

 the quantity has been much lessened of late years, through the cutting 

 down of old woods, and the influx of factory smoke, which appears to 

 be singularly prejudicial to these lovers of pure atmosphere. Notwith- 

 standing their dry nature and airy habitats, the Lichens are fond of 

 moisture, and on the commencement of rainy weather often spring up 

 like new creations. It is at such times, and in winter, when their 

 adhesion is somewhat relaxed, that the rock-loving species are best 

 procurable. At other seasons, chained like Prometheus, they can 

 seldom be brought away except upon fragments of the stone on which 



they grow. 



35 



