VSNEA.] 



201 



Tribe X. U S N E E I IS'yl. Mem. Soc. Cherb. iii. (1855) p. 170. 



Thallus fruticulose, somewhat rounded, rarely angulose, erect or 

 pendulous, internally with a firm chondroid axis. Apothecia leca- 

 norine, peltate, terminal or lateral : spores 8nse, small, simple, 

 colourless ; paraphyses not discrete. Spermogones immersed ; sterig- 

 mata simple or subsimple. 



A natural tribe, distinguished from its allies by having internally a 

 solid axis (as in Stercocaulon), which readily separates from the cortical 

 layer. Comprising only three small genera, two of which, Neuropoyon 

 and Chlurea, do not occur in Great Britain, it is with us, as in most other 

 countries, marked by the abundance of the species of Usnea. 



37. USNEA Dill. Muse. (1741) p. 56 pro parte ; Ach. Meth. 

 (1803) p. 306. Thallus filamentoso-elongate, or fibrilloso-ramulose 

 with patent branches, concolorous on both sides ; chondroid axis 

 composed of densely conglutinate filaments, cortical layer fragile 

 and often diffract. Apothecia concolorous or subconcolorous with 



Fig. 40. 



Usnea florida Ach. a. Longitudinal section of the thallus, X200. b. Vertical 

 section of a young apothecium (with thalline receptacle), x30. c. Theca and 

 paraphysis, X350. d. Spores, X500. e. Transverse section of the thallus, 

 showing above a spermogone (beneath which is a section of the medulla), 

 X30. /. Sterigmata and spermatia, X500. 



the thallus, often with ramuloso-ciliate margin ; hypothecium colour- 

 less ; spores small, ellipsoid ; paraphyses stipate in the dense 

 hymenial gelatine, which is bluish with iodine. Spermogones 

 lateral, slightly protuberant, in colourless conceptacles ; spermatia 

 straight, cylindrico-acieular, slightly incrassate towards the base. 



