II] 



ASCOMYCETES 



39 



e~- 



hymenium. In Desmotascus 1 , a pyrenomycetous fungus parasitic on Bromelia, 

 the paraphyses are replaced by a thin-walled pseudoparenchyma recalling 

 the arrangement in the higher Plectomycetes. 



The Peridium. The peridium or wall of the ascocarp is a weft of sterile 

 hyphae in which the individual 

 filamcntsare sometimes clear- 

 ly distinguished, sometimes 

 closely interwoven to form a 

 pseudoparenchyma; the walls 

 of the outer cells are some- 

 times considerably thickened 

 and may be variously pig- 

 mented ; in many cases they 

 give rise to hairs (Lachnea, 

 Ctiaetomiunt) or other ap- 

 pendages (Erysiphaceae). 



Alternation of Genera- 

 tions. The Ascomycetes show 

 a well-marked alternation of 

 generations modified by the 

 wide occurrence of apogamy 

 in the group. 



In forms where fertiliza- 

 tion is still retained the myce- 

 lium arising from the germination of the ascospores gives rise to the sexual 

 organs. These show a considerable variety of form and in the vast majority 

 of cases are clearly differentiated as male and female structures. The male 

 branch consists of an antheridial hypha or stalk and a terminal anthendium 

 which, in some of the more complex forms, is detached and carried by the 

 wind or otherwise as a spermatium. The female branch or archicarp 

 possesses a stalk of one or more cells, bearing the oogonium: sometimes 

 a terminal trichogyne is present by means < if which connection is established 

 between the oogonium and antheridium. The term ascogonium has been 

 used at various times as the equivalent of archicarp or oogonium, or to 

 indicate the oogonium after fertilization, but it does not appear essential in 

 any of these senses. In certain cases where the walls are partly broken 

 down between several cells in the middle of the archicarp, the term oogonial 

 region is applied to them. An archicarp of this type is sometimes known 

 as a scolecite. The gametangia each contain one or several nuclei, but 

 the contents are in no case rounded off as independent gametes. The 



1 1919, Stevens, F. I.., "Perithecia with an Interfascicular Pseudoparenchyma," Bet. Gazette, 

 lxvii, p. 422. 



Fig. 7. Lachnea stercorea (Pers.) Gill.; ascocarp in longi- 

 tudinal section showing young asci and paraphyses; the 

 oogonium is still recognizable; x 160. a. sheath, /'. para- 

 physes, c. ascus, d. ascogenous hyphae, e. oogonium, 

 f. stalk of archicarp. 



