60 



POPULAR HISTORY OF LICHENS. 



The Apothecium {anroQr]ic7], a repository) consists nor- 

 mally of two distinct parts, the Tkalamium {6aka[io^, a re- 

 ceptacle) and the Exciple [excipio, to receive) ; in some 

 cases the latter is absent. The thalamium is either typically 

 open, forming a more or less flattened, concave or convex 

 disc, as in the Gymnocarpous {tyvfjuvos, naked, and Kapirbs, 

 fruit) section of the Lichen family ; or it is typically closed, 

 forming a globular or nucleiform body, which opens in a 

 state of maturity by a minute ostiole or pore, or by an irre- 

 gular fissure w r ith lacerated edges, as in the Angiocarpous 

 section. The exciple is a capsule or envelope enclosing or 

 protecting the thalamium. In some cases it merely forms 

 a margin or border bounding its sides ; in others it consti- 

 tutes both base and border ; in the Angiocarpi (07709 or 

 dyyetov, a vessel) it forms a more or less complete globu- 

 lar envelope, which is designated the Perithecium {irepl, 

 round)* The exciple is said to be thalline when it is formed 

 of an extension of the cortical layer or other tissues of the 



* The perithecium is said to be entire when it quite surrounds the nuclei- 

 form thalamium ; dimidiate {dimidiatus , halved) when situated on the upper 

 or exposed half only. Leighton also applies the term to the carbonaceous 

 exciple of the Grapkidea>, which is entire when enclosing the sides and base 

 of the thalamium, to which it gives a proper margin, as in Opegrapha ; and 

 dimidiate when confined to the sides, the base being naked, as in Grapkis. 



