Thallogens.] 



LICHENALES. 



4o 



Alliance III. LICHENALES. — The Lichenal Alliance. 



Algae, §3. Lichenes, Juss. Gen. 6. (1789).— Lichenes, Hoffm. Enumerat. Lichenum, (1784); Acha- 

 rius Prodr. Lichen (1798) ; Id. Methodus, (1803) ; Id. Lichenogr. Vnivers. (1810) ; DC. Fl. Fr. 

 2. 321. a815) ; Fries in Act. Holm. (1821); Agardh Aph. 89. (1821); Eschioeiler Syst. Lich. 

 (1824) ; Wallroth Naturgesch. der Flechten. (1824) ; Grev. Flora Edin. xix. (1824); Meyer Uber 

 die Entivickelung, ^c. der Flecht. (1825); Fie Meth. Lich. (1825); Fries Syst. Orb. Veg.22i. 

 (182.5) ; Martins in Bot. Zeitun<], 193. (1826) ; Fie in Diet. Class. 9. 360. (1826) ; Fries Lichenoqr. 

 Europcea. (1831) ; Eschw. in Mart. Fl. Bras. 1. 51. (1833) ; Hooker Brit. Fl. vol. ii. pt. 1. 129. 

 (1833'; Endlich. Gen. p. 11; Link Ausgew. Anatom. Botan. abbiUl. fasc. 3. — Graphidea, 

 Chevalier Hist, des Graphiddes. (1824, &c.) 



Diagnosis. — Cellular flowerless plants, nourished through their xvhole surface hy the 

 medium in which they vegetate ; living in air ; propagated by spores usually 

 inclosed in asci, and ahvays having green gonidia in their thalhts. 



Perennial plants, often spreading over the surface of the earth, or rocks, or trees, in 

 dry places, in the form of a lobed and foliaceous, or hard and crustaceous, or leprous 

 substance, called a thallus. This thallus is formed of a cortical and medullary layer, 

 of which the former is simply cellular, the latter both cellular and filamentous ; in the 



crustaceous species the cortical and 

 medullary layer differ chiefly in tex- 

 ture, and in the former being co- 

 loured, the latter colourless ; but in the 

 fruticulose or foliaceous species, the 

 medulla is distinctly floccose, in 

 the latter occupj-ing the lower half of 

 the thallus, in the former enclosed all 

 round by the cortical layer. Repro- 

 ductive matter of two kinds ; 1, spoi'es 

 naked, or lying in membranous amy- 

 laceous tubes (thecse) immersed in 

 nuclei of the medullary substance, 

 which burst through the cortical 

 layer, and colour and harden by ex- 

 posure to the air in the form of little 

 discs called shields ; 2, the separated 

 These, called gonidia, or gongyh, are 



%,;>^^^^7 f^i^}^ I J 1 1^.-' \o,] )) it^^^vV/ ^ ^^ 



Fig. XXX. 



cellules of the medullary layer of the thallus. 



Fig. XXIX. -1. Shields of Variolaria amara ; 2, a portion of the thallus of the same plant ; o. a 

 piece of the thallus of Sticta pulmonacea, with lacunae and soredia ; 4. thallus of the same, bearing 

 shields : 5- shield of Opegrapha scripta ; 6. thallus of the same ; 7. shields, young and old, of Lecanora 

 perella ; 8. shields of Bzeomyces rufus ; 9. part of thallus of Peltidea canina ; 10. section of a shield 

 of Sticta pulmonacea ; 11. Podetia of Cenomyce coccinea; 12. section of a shield of Baeomyces rufus ; 

 13. shields of Endocarpon miniatum ; 14. thallus of the same. Chiefiy from Greville's Flora Edmensis. 



Fig. XXX.— Section of a shield of Parmelia parietina. Link. 



