CRYPTOGAMIA FUNGI. 135 



raised spot ; internally white. GREV. Syn. 1 9. Xyloma salicinum^ 

 PERS. Syn. 103. HOOK. Scot. ii. 9. GREV. FL Edin. 368. Crypt. 

 FL t, 118. f. 2. X. lewocreas, MOUG. and NEST. No. 175. 



Hob. On the upper side of the leaves of sallows, viz. Salix 

 caprea, aurita et prostrata, not uncommon. 



On the latter willow the spots are glossy, bullate, and very 

 like Rkytisma Andromedce. 



2. JR. acerinum, black, rugose, in large circular raised spots ; in- 

 terior white. GREV. Syn. 19. Xyloma acerinum, PERS. Syn. 104. 

 HOOK. Scot. ii. 9. GREV. FL Edin. 369. Crypt. FL t. 118. f. 1. 



Hal. On the upper side of sycamore leaves in autumn. 



The spots are often surrounded by a yellow halo. Dr GRE- 

 VILLE considers R. punctatum of authors as merely an ear- 

 lier state of this species. It is characterized by the spots 

 being much smaller, and placed at a little distance from one 

 another, thus forming an imperfect cluster. 



70. HYSTERIUM. 



OBS. The Hysteria are solid, sessile, and of a black colour, 

 readily recognised by their linear form furrowed down the mid- 

 dle. They closely resemble the fructification of the genus Ope- 

 grapha, and seem to differ from it principally by their want of a 

 crust. They grow on decayed wood, bark, and leaves ; and the 

 differences between the species are commonly so slight, that one 

 is tempted to believe these may arise merely from variations in 

 the structure of their sites. 



* On wood or baric. 



1. H. quercinum, bursting through the bark, elongate, flexuose, 

 somewhat ventricose, greyish-brown. PERS. Syn. 100. GREV. 

 Fl. Edin. 366. MOUG. and NEST. No. 367. 



Hab. On dead and rotted oak branches, which are much 

 roughened by the irregular manner in which this species 

 bursts the epidermis. 



2. H. lineare, subimmersed, crowded, generally placed parallel, 

 linear, straight or flexuose; the disk linear with tumid lips. GREV. 

 Crypt. Fl. t. 167. f. 2. 



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