64 



POPULAR HISTORY OF LICHENS. 



shall immediately speak. Sometimes its colour is similar 

 to that of the thallus ; more frequently it is dissimilar, and 

 of a miich more vivid or dark tint. The exciple however is 

 frequently of the same colour with the thallus, and is there- 

 fore dissimilar in colour to the thalamium, than which it is 

 thus usually paler or lighter. 



The Thalamium is made up of a series of elongated cells 

 or cellular bodies arranged vertically to its surface ; they 

 are in a state of close aggregation, and are united by means 

 of a mucous or glutinous matter ; they arise from the mi- 

 nute, spherical, somewhat irregular cells of a tissue, which 

 forms the base of the apothecium, and is hence denominated 

 the hypothecium. These bodies are called respectively thecm 

 (Otffcrj, a sac) and paraphyses (irapafyvGis, an offset). The 

 hypothecial cells, from which they spring, usually rest im- 

 mediately on the medullary layer of the thallus. 



The Paraphyses are elongated, linear, club-shaped bodies, 

 composed of a series of six or eight cylindrical cells, in ap- 

 position by their extremities, whose walls are delicate, and 

 whose contents are a hyaline mucous matter ; the terminal 

 cells — the aggregation of which constitutes the surface of the 

 thalamium — differ in being irregularly round, frequently 

 marked by wart-like bulgings, and in possessing coloured 



