230 ORGANOGRAPHY. BOOK I. 



tubes filled with sporules ; and, secondly, soredia, which are 

 heaps of pulverulent bodies scattered over the surface of the 

 thallus. The nomenclature of the parts of lichens has been 

 excessively extended beyond all necessity : it is, however, 

 absolutely indispensable that it should be fully understood by 

 those who wish to read the systematic writers upon the 

 subject : — 



1. Apothecia, are shields of any kind. 



2. Perit/iecium, is the part in which the asci are immersed. 



3. Hyjjothecium, the substance that surrounds, or overlies 



the perithecium, as in Cladonia. 



4. Scutelhim, is a shield with an elevated rim, formed by the 



thallus. Orhilla is the scutellum of Usnea. 



5. Pelta, is a flat shield without any elevated rim, as in the 



genus Peltidea. 



6. Tuherculum^ or cej)halodium, is a convex shield without an 



elevated rim. 



7. Trica, or Gyroma, is a shield, the surface of which is 



covered with sinuous concentric furiT>ws. 



8. Lirella, is a linear shield, such as is found in Opegrapha, 



with a channel along its middle. 



9. Patellula, an orbicular sessile shield, surrounded by a rim 



which is part of itself, and not a production of the thal- 

 lus, as in Lecidea. D. C. 



10. Globidus, a round deciduous, shield, formed of the thallus, 

 and leaving a hollow when it falls off, as in Isidium. D. C. 



11. Pilidium^ an orbicular hemispherical shield, the outside of 



which changes to powder, as in Calycium. D. C. 



12. Podetia, the stalk-like elongations of the thallus, which 



support the fructification in Cenomyce. 



13. Scypha {oplariiim. Neck.), is a cup-like dilatation of the 



podetium, bearing shields on its margin. 



14. Soredia {glohidi, glomeluri), are heaps of powdery bodies 

 lying upon any part of the surface of the thallus ; the 

 bodies of which the soredia are composed are called 

 conidia by Link, and propagida by others. 



15. Cystula, or Cistella, a round closed apothecium, filled with 

 sporules, adhering to filaments which are arranged like 

 rays around a common centre, as in Sphserophoron. 



