PARMELIA. 



193 



cavity is simple; their sterigmata small, not very ramose 

 filaments, formed of a series of rounded cubical cellules, like 

 those of Sticta ; their spermatia straight and developed in 

 large quantity from the individual articulations, that is, la- 

 terally from the sterigmata. When the spermogonal cavity 

 becomes empty, its sterigmata increase in size, coalesce, and 

 acquire a brownish colour. 



6. Pahmelia pulverulenta* {pulvis, dust or powder). 

 Thallus membranaceous-cartilaginous, olive-green, brownish 

 or reddish; when dry white or greyish-pruinose, — below 

 black-pannose ; lacinise linear-pinnatifid. Apothecium black- 

 ish-brown, greyish-pruinose, margin tumid or squamulose- 

 foliose. There is considerable variety in the characters of the 

 thallus ; the lacinise are sometimes very narrow r , elongated 

 and imbricate, or short, broadish, and rotundate-lobate ; 

 the thallus is sometimes non-pruinose ; at other times the 

 margin alone or the whole surface is more or less covered 

 with a whitish efflorescence. (E. B. 2064.) 



A common species, growing frequently on roadside trees, 

 especially old ash-trees, in lowland regions, and also, but 

 less commonly, on walls and rocks. In the neighbourhood 

 of Perth it is abundant both on roadside trees and walls. 



* The "Pulver-laf " of Scandinavia. 



O 



