ON THE GENUS USNEA, AND ANOTHEE (EUMT 



ALLIED TO IT. 



By JAMES STIRTON, M.D., F.L.S. 



AMONGST a parcel of lichens recently received from Mr 

 F. M. Bailey of the Colonial Museum, Brisbane, Queens- 

 land, I picked out what appeared, at first sight, as a very robust 

 state of Usnea eeratina, without, however, any of the characteris- 

 tic papillae. Sections of the stems and branches revealed the 

 fact that the thick corneous axis was hollow throughout its en- 

 tire extent, and only pervaded by the arachnoid medullary fibres, 

 while there were no such fibres surrounding this axis (their 

 invariable site in Usnea), but instead a thin, beautiful, and rather 

 dense ntfesccnt layer, outside of which was the usual gonidial 

 layer covered by the corneous cortex. Stimulated by this dis- 

 covery, I re-examined my collections of Usnea from other local- 

 ities, and detected plants from Madeira and tropical Western 

 Africa, which possessed identical relationships of the constitu- 

 tion of the stems. The rufescent stratum was also seen in all. 

 Now the only other genus to which such a series of lichens 

 could, in the present state of classification, be allocated, is 

 Chlorea (Nyl.), but a glance at the definition given in Nylander's 

 Syn. showed that Nylander could not have had in contemplation 

 such a series as this when he constituted the genus. In Chlorea, 

 one at least of the species is irregularly hollow, as Ch. vulpina ; 

 others, as Ch. Canariensis, have solid axes precisely as in Usnea. 

 In truth, the only constant characters that seem to warrant the 

 separation of Chlorea from Usnea are, ist, the flattened condi- 

 tion of the stems at the bifurcations ; and 2d, the more or less 

 scrobiculato-rugose aspect of the thallus generally, which con- 

 ditions are, nevertheless, seen to a certain extent in Usnea 

 angulata (Ach.) The only two species of Chlorea, as given by 

 Nylander in his Synopsis, that might be even distantly included 

 in the present series are the two last — viz., Ch. cladouioides. and 



