LICHENES. 



297 



393. i n their modes of reproduction, also, lichens agree 

 with the before-mentioned orders of the Ascomycetes. Like 

 them, they produce asci, containing ascospores, spermago- 

 nia, with their contained spermatia, and one or more other 

 organs whose functions are supposed to be reproductive. 



394. The asci are always developed from the hyphae, and 

 have no connection whatever with the gonidia. They arise 

 in most (but not all) cases from the hyphaa of the interior of 

 the lichen. It appears that the particular hyphae which 

 produce asci differ from those which are found elsewhere in 

 the lichen in being of greater diameter and richer in proto- 



Fig. 203. Vertical section through the young apothecinm of Lecanora trtibfusca 

 (partly diagrammatic) ; h, h, hymenium, composed of (1) paraphyses, which de- 

 veloped from the ordinary hyphse, and (2) the young asci in various stages of de- 

 velopment ; sh, ascophorous hyphae, from which the asci develop; e, excipulum i.e., 

 the layer of hyphse upon which, or above which the ascophorous hyptue are borne ; 

 r, r, cortical layer of thnllus ; m. medullary portion of thallus ; a. the gonidia. X 190. 

 After De Bary. 



plasm. The asci are developed from vertical, club-shaped 

 branches, which penetrate between narrow, vertical branches 

 (paraphyses) of the ordinary hyphss (Fig. 203). In many 

 cases they are collected in a disc-like surface, forming an ex- 

 posed hymenium (gymnocarpous lichens), while in other cases 

 they are in the interior of cavities (perithecia), whose walls 

 they line (angiocarpous lichens). The ascigerous fructifica- 

 tion is in either case technically called an apofhecium. 



395. The spores arise in the asci exactly as in the case of 

 Peziza and other Ascomycetes previously described ; that is, 

 they are formed simultaneously by the condensation of the 

 protoplasm about certain points in the interior of the young 



