COLLEMA. 



279 



resembles the frond of many chlorospermous seaweeds, and 

 here the chlorophyll, which in most Lichens is confined to 

 the gonidia, is diffused through, or dissolved in, the thalline 

 mucilage. Other Collemas have a thallus of a leathery or 

 cartilaginous consistence, more resembling the normal or 

 typical Lichen-thallus in structure. In some species the 

 thallus is naked ; in others, granulose or furfuraceous ; and 

 in a few, papulose or marked on the surface by pellucid 

 papules or vesicles, which Schserer regards as in some 

 way subserving, like the gonidia, the function of reproduc- 

 tion. The apothecium is usually developed in a thalline 

 wart, and is at first globose, becoming gradually expanded, 

 open, and discoid. In species having a thick and dense thal- 

 lus it is generally scutellate, having a distinct thalline ex- 

 ciple ; but in other cases this exciple is very thin, pellucid, 

 evanescent, or it is covered by the thalamium, which becomes 

 flattened and then convex (patellseform) . In a few a proper 

 exciple has been described, in which case the apothecium is 

 patellate. 



* Thallus filamentous ; apothecia patellaform. 

 1. Collema pubescens {jpubesco, to become mossy or 

 downy). Thallus black, decumbent. Klaments capillaceous, 

 terete-elongate, somewhat simple, entangled or loosely inter- 



