PEZIZALES 339 



Ascodesmis nigricans, while Lasiobolus (Cubonia) brachyascus have 

 unicellular ascogonia and trichogynes, like Pyronema confluens (Satina, 

 1921). The antheridium is multicellular, coiling helically about the 

 trichochyne with which it copulates. In still other species have been 

 found developmental forms for which there are at present no parallels 

 in the Pyronemaceae but for which we find complete and significant 

 analogies in the Plectascales. Thus in Thelobolus Zukalii and some spe- 

 cies of Rhyparobius (Ramlow, 1915), the antheridia and ascogonia twine 

 helically, as in Peniciilium crustaceum. In Ascobolus magnificus (B. O. 

 Dodge, 1920), finally, the morphological relationship is reminiscent of 

 Amauroascus. This species is interesting because it is heterothallic. 

 Single spore cultures do not produce apothecia; these appear shortly 

 if the complementary mycelium is present. 



Four to six days after the sowing, there appear on the hyphae short, 

 clavate, one- to two-celled branches which stand vertically from the sub- 

 strate. In a few hours they increase considerably in length; one branch, 

 the antheridium, usually remains vertical; the ascogonium, if it is in the 

 immediate vicinity coils about the antheridium (Fig. 225, 3) or, if 

 it is further away, its tip grows toward and coils about the antheridium 

 (Fig. 225, 4 and 5). In both cases the trichogyne comes into open com- 

 munication with the antheridium, whereupon the ascogenous hyphae 

 grow out of a cell nearer the base (Fig. 225, 6 and 7). All these types, 

 however different their external forms, have in common a well-developed 

 amphimixis which, at least in Ascobolus magnificus, shows a physiological 

 sexual differentiation, heterothallism. 



In numerous other forms, there appear successively all sorts of degen- 

 eration phenomena such as are numerous in previously described 

 Ascomycetes: the antheridia disappear and in place of the original 

 amphimixis, appear various kinds of deuterogamy; at first a modified 

 amphimixis, for which no term exists (Ascobolus carbonarius type), then 

 parthenogamy, in which cell fusion occurs between two female sexual 

 cells, then autogamy in which cell fusion is absent and nuclear pairing 

 occurs within a single sexual cell and finally pseudogamy (at least in the 

 Pezizaceae) in which vegetative hyphae copulate. 



Ascobolus carbonarius is one of the theoretically most important forms 

 of fertilization of the higher Ascomycetes because it facilitates an under- 

 standing of sexuality of the lichens. The ascogonium, in the absence of 

 antheridia, grows toward conidia, surrounds them and apparently copu- 

 lates with them. Thus Fig. 226, 1 shows a stipitate ascogonium, sur- 

 rounded by sheath hyphae, which itself has arisen directly from the germ 

 tube of a eonidium C\) it has formed toward the left a very long tricho- 

 gyne which then surrounds another eonidium C 2 . Hereupon the asco- 

 genous hyphae grow from some basal cell of the ascogonium. The 

 ascogonium in Fig. 226, 3, showing such a relationship, has ceased develop- 



