626 COMPARATIVE MORPHOLOGY OF FUNGI 



Caryogamy and meiosis remain constant, however, in form and place. 

 Correspondingly, the gonotoconts, the asci, show a remarkable stability 

 in the mobile series of sexual organs and fructifications. After the 

 Hemiascomycetes, where they have been stabilized to a definite form and 

 spore number, they alone further undergo a development and secondary 

 modifications in function (p. 135) but remain entirely the same in morpho- 

 logical features. The fact that this biological differentiation of the asci 

 is retained while the imperfect forms are wanting, causes the position 

 of the asci as perfect forms to appear more strongly ; one has the impression 

 that more weight would be placed on a suitable dissemination of asco- 

 spores (as the products of fertilization) than on the dissemination of 

 conidial forms. 



It appears, however, that the same laws which in the Choanephora 

 Blakeslea group (pp. 101-102) retarded spore r formation and shifted it to 

 the exterior of the sporangia, must have gradually become active in the 

 sporangia, the asci, which have become gonotoconts: in the Cunning- 

 hamella-Syncephalis-Aspergillaceae series, spore formation is shifted 

 from the interior of the sporangia to their surface so that the sporangio- 

 phores became conidiophores. In time the asci also shifted their spore 

 formation to the surface and thus became changed from sporangia to 

 conidiophores (at first eight spores), to basidia. The basidium thus 

 would be an ascus with exogenous spore formation. The usual 

 Zygomycetous sporangia and the sporangia which have become gonoto- 

 conts (asci) would have gone through the same development from endo- 

 genous to exogenous spore formation; only in the usual sporangia this 

 development occurred in a short span of time (genetically considered) 

 while the sporangia which have become gonotoconts, because of their 

 greater stability, became active much later. Apparently in this manner 

 the lower Basidiomycetes have arisen from forms like Ascocorticium in the 

 lower Ascomycetes. 



The life cycle of these lower Basidiomycetes agrees entirely with 

 that of the Euascomycetes. On the germination of their tetracytes, 

 there first arises a haploid thallus whose structure appears entirely like 

 that of the Euascomycetes and which propagates by imperfect forms 

 fundamentally the same as those of the Euascomycetes (p. 397). Sub- 

 sequently pseudogamous plasmogamy, occurring between its hyphae 

 (as between the hyphae of the Euascomycetes), produces new dicaryotic 

 hyphae; in both the Euascomycetes and the Basidiomycetes, sexual 

 organs are suppressed and as evidence of earlier sexuality, there is only 

 retained the dynamic differentiation of the mycelia into + and - strains 

 (heterothallism). This dynamic differentiation, however, begins to lose 

 its obligatory character and instead of the original antithetic (bipolar) 

 sexual differentiation, there appears the multipolar (p. 399) which rests 

 only on comparatively labile and dynamic gradations. 



