STRUCTURE.] LICHENS. 117 



valves, which discover, upon opening, a subulate columella, 

 to which sporules are attached without any elaters. There 

 are also cystulae upon the frond, in which are inclosed pedi- 

 cellate reticulated bodies, called anthers. 



Sphasrocarpus consists of a delicate roundish frond, on the 

 surface of which are clustered several cystulse, each of which 

 contains a transparent spherule filled with sporules. 



In Riccia the spherules are not surrounded by cystulae, but 

 immersed in the substance of the frond. 



4. THE LICHENAL ALLIANCE.* 



(Lichens.) 



These have a lobed frond or thallus (or blastema), the inner 

 substance of which consists wholly of reproductive matter, 

 that breaks through the upper surface in certain forms which 

 have been called fructification. These forms are twofold; 

 firstly, shields (scutella or apothecia), which are little coloured 

 cups or lines with a hard disc, surrounded by a rim, and 

 containing asci, or tubes filled with sporules ; and, secondly, 

 soredicij 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, desirable that it should be understood by those 

 who wish to read the systematic writers upon the subject. 



1. Apothecia, are shields of any kind. 



2. Perithecium, is the part in which the asci are contained. 



3. Hypothecium ; the substance that surrounds, or overlies 

 the perithecium, as in Cladonia. 



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

 thallus. Orbilla, is the scutellum of Usnea. 



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



genus Peltidea. 



6. Tuber culum, or Cephalodium, is a convex shield without an 

 elevated rim. 



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

 grooved with sinuous concentric furrows. 



* Vegetable Kingdom, p. 45. 



