168 A CONTBIBtTTION TO, ETC. 



(5) Lecanora comprises a genus not so easily distinguished as 

 the preceding, and the species here are much smaller than some 

 already enumerated. The name of this genus is taken from le- 

 cane, a dish or platter, in allusion to the form of the apothecium. 

 Two species L. atra and Z. subfusca, are very common, and they 

 may be found on trees, rocks, fences, and sometimes even on the 

 ground. The apothecia of these appear very much alike both 

 eventually becoming black, though in L. subfusca they are not 

 so ab initio. It is almost impossible to examine the bark of trees 

 or the rocks without noticing the small black shield-like bodies 

 which constitute the sporangia of these lichens. L. subfusca may 

 be termed cosmopolitan, and Dr. Hooker states in his work on 

 the Cryptogamic Antarctic Flora, that it is one of those plants 

 which with a few mosses, comprise the last remnants of vegeta- 

 tion in the Southern Hemisphere. 



(6) Lecidea is another genus which takes its name from the 

 form of its apothecia, which are supposed to resemble a dish 

 (Lecos a dish and eidos like). The apothecia are black, nattish 

 and marginate or uniform. The species which I have noticed on 

 the sandstone rocks to the north of Parramatta, appears similar 

 to the L. petrcea of Europe, and it is evidently nearly allied to L. 

 geograpliica, but differing from that species in the colour of the crust, 

 and the shape of the apothecia. When viewed with the naked 

 eye, this lichen appears on the rock as a white patch, with 

 innumerable black specks on it, but under a lens the thallus has a 

 somewhat tessellated appearance, and the black specks are seen 

 as apothecia grown into the crust, with a tumid elevated contracted 

 margin. I have been thus particular in describing the appear- 

 ance of this diminutive plant, as I believe it to be one of those 

 insignificant but wonderful agents employed by Divine Provi- 

 dence for the disintegration of rocks, and the gradual prepara- 

 tion of a humble soil for mosses and other plants. This opinion 

 I mentioned some little time since to my eminent geological 

 friend the Rev. "W. B. Clarke, and I was pleased to find that he 

 agreed so far with me, as to attribute much importance to the 

 slow and almost imperceptible changes affected by " mosses." 

 Since that- conversation, I have had an opportunity of reading a 

 late work on British Lichens, and in that I find several inter- 

 esting facts, mentioned in reference to the genus Lecidea, which 



