DEVELOPMENT OF APOTHECIA 



183 



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wall or " proper margin " round the spore-bearing disc. The branching of 

 the hyphae is fastigiate with compact 

 shorter branches at the exterior. In 

 such an apothecium gonidia are ab- 

 sent both below thehypothecium and 

 in the margins. 



In lecanorine development the 

 ascending hyphae from the medulla, 

 in some cases, carry with them algal 

 cells which multiply and spread as a second gonidial layer under the hypo- 

 thecium (Fig. 102). These hyphae may also spread in a radial direction 

 while still within the thallus and give rise to an "immersed" apothecium 

 which is lecanorine as it encloses gonidia within its special tissues, for 

 example, in Acarospora and Solorina. But in most cases the lecanorine fruit 

 is superficial and not unfrequently it is raised on a short stalk {Usnea, etc.); 



Fig. loi. Lecidea paras ema Ach. Vertical section 

 of thallus and apothecium with proper margin 

 only X ca. 50. 



Fig. 102. Lecanora iartarea Ac\i. Vertical section of apo- 

 thecium. a, hymenium ; b, proper margin or parathecium ; 

 €, thalline margin or amphithecium. x 30 {after Reinke). 



both the primary gonidial zone of the thallus and the outer cortex are asso- 

 ciated with the medullary column of hyphae from the first and grow up 

 along with it, thus providing the outer part of the apothecium, an additional 

 " thalline margin " continuous with the thallus itself It is an advanced 

 type of development peculiar to lichens, and it provides for fertility of long 

 continuance which is in striking contrast with the fugitive ascocarps of the 

 Discomycetes. 



The distinction between lecideine and lecanorine apothecia is of great 

 value in classification, but it is not always easily demonstrable; it is 

 occasionally necessary to examine the early stages, as in the more advanced 

 the thalline margin may be pushed aside by the turgid disc and become 

 practically obliterated. 



