394 COMPARATIVE MORPHOLOGY OF FUNGI 



protoplasm, as in the sporangial protoplasm of Polyphagus and the 

 Mucoraceae would have been divided by direct cleavage into the individual 

 spore, portions. The nuclei in the young ascus of Dipodascus are not 

 equivalent to each other, however, since true ascospore nuclei, i.e., prod- 

 ucts of the sexual act and meiosis, and ordinary vegetative or sexually 

 inactive gametangial nuclei appear side by side or intermingled. In such 

 a cleavage the vegetative and ascospore nuclei would both enter into the 

 ascospores. This could be avoided only by free cell formation. 



According to this conception, free cell formation in the higher Oomy- 

 cetes and in the ascospores of Dipodascus is only a convergence phenome- 

 non, since in coenocytic gametangia, only a selected number of sexual 

 nuclei participate in fertilization, while the others are vegetative and do 

 not enter the new organs (egg cells, ascospores). The ascus of the Dipo- 

 dascus and of the Ascomycetes altogether and the oogonium of the Oomy- 

 cetes are analogous not homologous organs, as Bary assumed. Whether 

 in both cases the cytological processes are identical to the smallest detail, 

 can be explained only by a closer investigation of Dipodascus. 



From the Dipodascus type a further stabilization of the ascus has 

 occurred since its spore number, corresponding to the number of the 

 tetracyte nuclei, is fixed at eight. The ascus is phylogenetically a germ 

 sporangium become gonotocont, with the correspondingly fixed spore 

 number. Thus the sporangia of the Zygomycetes would have undergone 

 a cleavage, those which normally served further as imperfect forms gradu- 

 ally change to conodiophores as in the Choanephora-Aspergillus-Peni- 

 cillium series; those which functioned as gonotoconts, however, retained 

 their sporangial character at first and only lost it later in the transition 

 from Ascomycetes to Basidiomycetes. In contrast to this morphological 

 stability, biologically the ascus undergoes a manifold functional develop- 

 ment which reaches its high point in the discharge organs of the 

 Discomycetes. 



In the second place, from the Dipodascus type, a development of the 

 female copulation branch (e.g., differentiation into the ascogonium and 

 trichogyne) has occurred while the male copulation branch shows a great 

 constancy and degenerates early. Consequently, in place of the original 

 gametangial copulation, there appear all sorts of deuterogamous processes, 

 the most noteworthy of which is copulation with conidia. The fact that 

 in certain parthenogamous forms the trichogyne is lacking, while in others 

 it has reached a high degree of development, leads one to suppose that in 

 the latter it was made to serve secondary purposes. 



In the third place, the retardation of caryogamy which has already 

 caused fertilization to be transferred from the gametangium to ascus 

 continues still further, so that meanwhile the dicaryon divides repeatedly. 

 Consequently the gametangia do not develop directly to asci, but, in a 

 certain sense, vegetatively to dicaryotic hyphae, the ascogenous hyphae, 



