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MYCOLOGY 



CETALES, which have been derived in ail probability from an alga 

 like Vaucheria with oogonia and antheridia, where the male sexual 

 organs are smaller than the female. To derive the ZYGOMYCE- 

 TALES from such a group would necessitate that the sexual organs 

 become of equal size. 



Entomophthora is a connecting form where the sexual organs ap- 

 proach each other in size. This genus is then connected by insensible 

 difiEerences with the heterogamic hermaphroditic moulds where there is 

 an appreciable difference in the size of the two cells that conjugate, the 

 larger being the female, the smaller the male, as in Absidia spinosa and 

 Zygorhynchus heterogamus. These are directly connected with the 

 homogamic hermophrodite moulds and these with the homogamic 

 heterothallic forms. The polyphyletic view necessitates the deriva- 

 tion of the OOMYCETALES from a Vaucheria-like ancestor, and the 

 ZYGOMYCETALES from a Zygnema-like ancestor, where conjugation 

 of similar cells (gametes) is found. The polyphyletic origin of the 

 fungi is emphasized by the adherents to the doctrine of the origin of the 

 AscoMYCETALES from red algae, as there are three points of contact: 

 first, sac fungi with highly developed trichogyne (sterilized archicarp) of 

 the Collema type with red algae-like certain existing forms; second, sac 

 fungi with highly developed trichogyne of the Poly stigma tj^e; third, 

 sac fungi with simple generalized copulating gametes of the Gymnoascus 

 type. We are, however, not in the position to name any known red 

 alga as the progenitor of the sac fungi, and it is far more reasonable to 

 search for one in another fungous line, where, in the light of present-day 

 knowledge, there are known forms with sexual organs very much like the 

 sexual organs of simple, known forms of the Ascomycetales. We are 

 not now in a position to name any known phycomycete as a probable 

 ancestor, though the likelihood is that the original stock possessed phy- 

 comycetous characters, thus attributing a monophyletic origin to them. 

 One of the most instructive forms suggesting a mode of transition from 

 the PHYCOMYCETES to the ASCOMYCETALES, is Dipodascus. 

 Its sexual organs are strikingly like those of certain Mucorace^ or 

 PERONOSPORACE.E in their young stages. The sexual organs can be 

 recognized as antheridium and oogonium either from the same thread 

 (homothallic) or from different threads (heterothallic). After absorption 

 of the wall between the gametes, the fertilized oogonium (or zygote) 

 grows out into an elongate stout ascus, or zygogametangium with the 



