8 Rev. W. A. Leighton on British Lichens. 



II. — Notes on British Lichens. 

 By the Rev. W. A. Leighton, B.A., P.B.S.E. 



[Plate IV.] 



I purpose, in this and subsequent papers, from time to time to 

 present notes and illustrations of new or recently discovered 

 British Lichens, or such as have not been figured and described 

 in Sowerby's 'English Botany ' and Supplement. 



Gonionema, Nyl. 



Thallus filiform ; gonidial cells large, filled with granules, con- 

 catenated into a central axis. Apothecia biatorine or gyalec- 

 toid. 



Gonionema velutinum, Nyl. Thallus dark brown, slender, en- 

 tangled ; apothecia dark brown, terminal, centre depressed, margin 

 swollen, pale within ; sporidia in asci 8, ellipsoid, simple, colour- 

 less; paraphyses slender. 



Gonionema velutinum, Nvl. Prodr. 16 (1857), Syn. 88, 1. 1. fig. 11 (1858), 



Scand. 23 (1861). 

 Collema velutinum, Ach. Syn. 329 (1814). 



On the northern precipices of Craig Breidden, Montgomery- 

 shire, June 1864. 



This minute lichen grows in scattered or continuous patches 

 on the face of the rock, and resembles in general appearance a 

 coarse dense velvety pile, of a blackish-brown colour. It con- 

 sists of minute, slender, cylindrical filaments, simple or branched, 

 erect, uniform in height, crowded and entangled into a casspitose 

 mass. When moistened and viewed under the microscope, these 

 filaments are found to consist of an outer fleshy or cartilaginous 

 continuous membrane, of a darkish-brown or olive-tawny colour, 

 within which is seen a central axis filling the entire external 

 cylindrical membrane, formed of large globular or spherical cells 

 concatenated in a moniliform manner, compressed longitudinally 

 by juxtaposition, and thus giving the cells a transverse dilata- 

 tion. On the external membrane being ruptured, the central 

 axis in longer or shorter lengths extrudes itself, and is then seen 

 to be of a pale dirty glaucous-green colour, and the cells to be 

 filled with very minute spherical granules, which, on the appli- 

 cation of diluted sulphuric acid, become of a reddish tinge. I 

 did not observe any apothecia on the Breidden specimens; but 

 the structure of the thallus in these so corresponds with an 

 authentic specimen in fructification, received from Dr. Nylander 

 himself, as to leave little or no doubt of their identity, notwith- 

 standing a slight difference in the width of the filaments, most 

 probably resulting from age and situation. The apothecia on 



