210 CLASS ASCOMYCETEAE 



produce the marginal tissues of the apothecium. The body of the apothe- 

 cium consists then of the several oogones and the branched ascogenous 

 hyphae which grew out of these, of the antherids, and of the vegetative 

 hyphae which arose from the supporting cells of the oogones and an- 

 therids. These latter form the main body of the apothecium as well as 

 its paraphyses. In the excipulum these hyphal cells by lateral enlargement 

 and mutual pressure form a pseudoparenchymatous tissue. (Fig. 70.) 



It may seem strange that so common a species, the object of numerous 

 investigations by different investigators, should still be the subject of 

 so much disagreement. Perhaps the difficulty of staining well the rather 

 small nuclei and the rapidity of the progress of the sexual phenomena 

 are responsible for the greater part of the difficulty encountered. To this 

 must be added the fact that many of the stages of development, if the 

 exact sequence is not certain, could be interpreted differently if considered 

 as belonging to an earlier or later stage. Furthermore, an investigator, 

 with the best will possible, is apt to interpret what he sees in the light 

 of what appears to him to be the most logical series of events. 



Using the phenomena just described for Mycosphaerella and Pyronema 

 as a basis for comparisons we find that sexual reproduction has been 

 modified in several different ways in the Ascomyceteae. Thus the antherid 

 when present may not be a functional organ. This is clearly the case in 

 the variety inigneum of Pyronema omphalodes in which W. H. Browm 

 (1915) has shown that there is no opening between antherid and tricho- 

 gyne and frequently no contact. Dangeard denies the functioning of the 

 antherid in the whole class except in the order Saccharomycetales. He 

 accounts for the pairs of nuclei in the oogone and ascogenous hyphae as a 

 pairing of the female nuclei, which seems to be beyond doubt the case 

 in the variety of Pyronema just mentioned. For Dangeard the only 

 nuclear fusion is that occurring in the ascus. For those following Claussen 

 this is the true nuclear fusion (karyogamy), but the union of antherids 

 and oogone is looked upon as a true sexual fusion also (cytogamy). 

 Harper and Gwynne-Vaughan and Williamson believed cytogamy and 

 karyogamy to occur one just after the other, with a second nuclear fusion 

 occurring in the ascus. 



There is a marked tendency toward the production of a more or less 

 coiled series of cells, usually considerably greater in diameter than the 

 cells of the vegetative mycelium and often tapering to a long slender, 

 multicellular trichogyne. Such a structure is called an ascogonium and the 

 cell out of which the ascogenous hyphae bud may properly be considered 

 the true oogone. This may be multinucleate or uninucleate. In the Laboul- 

 beniales, a few genera of the Lecanorales, and apparently also in a few 

 of the Pezizales and Sphaeriales, minute nonmotile sperms are produced 

 internally or externally on short antheridial branches and upon reaching 



