418 



BOTANY 



1. Aseoliehenes 



Only a few genera of Lichens have flask -i shaped peritheeia, the fungus lie- 

 longing to the Pyrenomycetes (Endocarpon, Verrucaria). Most genera produce, as 

 the ascus- fruit of their fungus, cupular or discoid apotliecia, sessile or somewhat 



Fi. 369. I'etraria island ica. 



(Nat. sixc.) 



up, Ajiotlii'ciuni. 



Fio. 3C.S. Usnea tiarbata. op, Apothecium. 

 (Nat. si/e.) 



sunk ill the thallus. In structure they resemble those of the Pezizeae. and 

 bear on their upper side an hymenium of asci and paraphyses. One of the 

 commonest species of fruticose Lichens belonging to this group is Usnea burlnitu, 

 the Beard Lichen, frequently occurring on trees and having large, fringed apotheeia 

 (Fig. 368). Kocf.Ua tinctoria, found widely distributed on the rocks of the 

 African coast and East Indies, has an erect, vermi- 

 form, forked thallus from which litmus and orchil 

 (orseille) are obtained. Cetraria -islaml'int, Iceland 

 Moss (Fig. 369), occupies an intermediate position 

 between the fruticose and foliaceous Lichens. It 

 has a divided, foliaceous but partially erect thallus, 

 which is of a light bluish-green or brown colour, 

 whitish on the under side, and bears the apothecia 

 obliquely on its margin. This Lichen is found in 

 Fio. 370. Clndonia. coccifera. mountainous regions in the northern part of the 

 t, Scales of primary thallus. Xortheru Hemisphere, and also at Cape Horn ; it 

 (Nat. si/..-.) -..11 v ,j 



has an official value as a demulcent. Xuiitlwrui 



parietina (Fig. 367) may be taken as an example of one of the commonest of 

 the foliaceous Lichens. The thallus is orange - yellow in colour, and bears 

 numerous apothecia on its central portions. Graphis script a is a well- known 

 example of the crustaceous Lichens; its greyish - white thallus occurs on the 

 bark of trees, particularly of the Beech, on whose surface the apothecia are 

 disposed as narrow, black furrows resembling writing. To the crustaceous Lichens 

 belongs also Sphacrothallia csculenta, growing on rocks in the steppes and deserts 

 of North Africa and Asia. The thallus falls into small pieces the size of a pea 



