SECT. I 



CRYPTOGAMS 



419 



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

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

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

 eoninionest species of fructicose Lichens belonging to this group is Usnca harhata, 

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

 (Fig. 356). Eamalina fraxiiica which has a broad ribbon-shaped branched thallus 

 and grows on trees, and the numerous species of Roccellcc found on the rocks of 

 warmer coasts, have similar apothecia. Cctraria islandica, Iceland Moss (Fig. 357), 

 occuides 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 mountainous regions and in the 

 northern part of the Northern Hemisphere. Xanthoria parietina (Fig. 355) may be 



Fig. 350. — Usnca harhata. ap, Apotliecium. 

 (Nat. size.) 



Fi(i. 357. — Cetraria islandica. ap, Apotliecium. 

 (Nat. size.) official. 



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. 

 Grajjhis scripta 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. 



A peculiar mode of development is exhibited by the genus Gladonia (^^), whose 

 primary thallus consists of small horizontal scales attached directly to the ground, 

 from which rises an erect portion, the podetium, of varying form and structure in 

 the different species. In some cases the podetia are stalked and funnel-shaped, 

 bearing on the margin or on outgrowtlis from it knob-like apothecia, which in 

 C. pyxidata are brown, in C. coccifera (Fig. 358) bright red. In other species the 

 erect podetia are slender and cylindrical, simple or forked ; in C rangiferina. 

 Reindeer Moss, which has a world-wide distribution, particularly in the tundras 

 of the North, the podetia are finely branched (Fig. 359), and bear the small brown 

 apothecia at the ends of the branches. The primary thallus of this species soon 

 disappears. 



The ascus-fructifications (apothecia or perithecia) of the Lichens originate, as 



2 El 



