LICHENS ANAPTYCHIA . 



337 



is occupied by a medulla, or "pith," formed of a looser hyphal 

 texture. We prepare median longitudinal sections through the 

 apothecium. This shows us the apothecial support formed of 

 the tissue of the thallus. The gonidial layer extends to its 

 rim, which grows out in places into ciliary outgrowths. The 

 apothecial support has expanded into a bowl-like form, in order 

 to admit the hymenium, which arises from the medullary tissue. 

 The hymenium is recognisable by its somewhat brownish colour. 

 It consists of very numerous, long, exceedingly narrow, septate 

 threads the paraphyses ; between these, but far less numerous, 

 stand the club-shaped sacs the asci. These latter are always of 

 various ages ; the ripe ones contain eight brown-walled spores 

 ascospores. These spores are elliptic, two-celled, slightly con- 

 stricted at the boundary of the two cells. Paraphyses and asci 

 arise from a like-coloured, felted, horizontally expanded layer of 

 little thickness, which is distinguished as the sub-hymen ial layer. 

 This originates from the medullary tissue of the stalk, from which 

 it is delimited by its brownish colour and the want of air-contain- 

 ing spaces. While, as we have seen, the hyphae of the thallus 

 itself are not coloured blue even by chlorzinc iodine (p. 240), 

 those of the hymenial tissue take a dark-blue colour, even with 

 the addition of a little iodine. The walls of the hymenial ele- 

 ments are formed of a 

 special modification of 

 cellulose, which has been 

 distinguished as starch- 

 cellulose. 



If we examine the 

 thallus of Anaptychia 

 ciliaris with the lens, we 

 shall notice here and there 

 upon it wart- shaped pro- 

 minences, standing singly 



or in groups. If in such 



-j v Fla 121. Cross-section through the thallus of 



places delicate cross-sec- Anap tychia dlians. 

 tions are taken in con- 

 siderable numbers, we shall probably cut through such a swelling 

 (Fig. 121). It appears then as an ovate structure, sunk in the 

 thallus, and opening outwardly with a pore, and is now known 

 as a pycnidium, It occupies almost the entire depth of the 

 thallus, is laterally surrounded by the algal layer, and in the 



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