REPRODUCTIVE ORGANS 



157 



size, rarely more than i cm. in diameter (Fig. 88); there is no development 

 in lichen fruits equal to the cup-like ascomata of the larger Pezizae. In 



** **tLf- Ar^>- . ,,. f % 



X A 



Fig. 88. Lecanora subfusca Ach. A, thallus and apothecia x 3 ; 

 B, vertical section of apothecium. a, hymenium; i>, hypo- 

 thecium ; c, thalline margin or amphithecium ; d, gonidia. 

 *. 60 (after Reinke). 



most cases the lichen apothecium retains its vitality as a spore-bearing 

 organ for a considerable period, sometimes for several years, and it is 

 strengthened and protected by one or more external margins of sterile 

 tissue. Immediately surrounding the fertile disc there is a compact wall of 

 interwoven hyphae. In some of the shorter-lived soft fruits, as in Biatora, 

 this hyphal margin may be thin, and may gradually be pushed aside as the 

 disc develops and becomes convex, but generally it forms a prominent rim 

 round the disc and may be tough or even horny, and often hard and car- 

 bonaceous. This wall, which is present, to some extent, in nearly all lichens, 

 is described as the "proper margin." A second "thalline margin" containing 

 gonidia is present in many genera 1 : it is a structure peculiar to the lichen 

 apothecium and forms the amphithecium. 



At the base of the apothecium there is a weft of light- or dark-coloured 

 hyphae called the hypothecium, which is continued up and round the sides 

 as the parathecium merging into the "proper margin." It forms the lining 

 of a cup-shaped hollow which is filled by the paraphyses, which are upright 

 closely packed thread-like hyphae, and by the spore-containing asci or tkecae, 

 these together constituting the thecium or hymenium. The paraphyses 

 are very numerous as compared with the asci ; they are simple or branched, 



1 See also p. 166. 



