COLLEMA. 



281 



regarded as a dioecious species. - * Indeed in the speculative 

 but laborious dissertation of Bayrhoffer (' Einiges iiber Li- 

 chenen und deren Befruchtung/ Berne, 1851) Lichens are 

 described as normally monoecious and dioecious. 



Thallus foliaceous, when dry membranaceous, when moist 

 flaccid; ajpothecia patellaform and scutellate, 

 2. Collema ATRO-CLERULEUM. Thallus very thin and 

 somewhat diaphanous, lacerate-laciniate, reticulate-lacunose, 

 from lead-coloured becoming reddish, when moist olive- 

 coloured. Apothecia patelkeform, minute, superficial, pale 

 brown. The lacinise vary in size, being sometimes narrow 

 and imbricately arranged ; in the most common variety, var. 

 lacerum, they are broadish, sinuate, with dentate-ciliate mar- 

 gins. 



Creeping over moss, and also growing sometimes on trees, 

 rocks, and the ground in various Highland districts. This 

 is one of the species possessing a distinct cortical layer, 

 composed of intimately united, polyhedral cellules, while the 

 medullary tissue resembles the filamentous texture of the 



* Eor minute anatomy and synonymy, vide Bornet, ' Annales des Sciences 

 Naturelles,' vol. xviii. 1852, p. 155 : Berkeley, in Annals of Nat. Hist. 

 1851 : Flotow, Bot. Zeitung, 1850, and ' Linosea, 5 1850 : Davies, on L. sca- 

 ler and some of its allies, in Trans. Linn. Soc. London, 1815. 



