ATKINSON: THE GENUS ENDOGONE 5 
of Endogone presages the beginning of a new structure, not more so 
than does the zygote of Piptocephalis and of certain species of Empusa, 
etc., but it is still homologous with the zygote of the other phyco- 
mycetes. 
In the Mucorales, aside from the meiotic divisions of the fusion 
nuclei, the process of sporulation in the germ sporangium (sporangium 
formed on germination of the zygote) is the same as that in the ‘“‘asex- 
ual’’ sporangium. The germ sporangium and the asexual sporangium 
are morphological equivalents. The germ sporangium is not a new 
morphological structure, though the zygote and early stages of its 
germination presage the origin of a new morphological structure. 
Historical experience turns it quickly back into the well-worn trail. 
The very simple primordium of the new structure does not mark out a 
new path until the accumulation of new experiences, together with 
environment, provide the threshold for progress to the new structure. 
If nuclear fusion does not occur in the azygotes of Endogone then 
the chromosome history, so far as we know, would run from generation 
to generation without change. The two situations may be repre- 
sented thus: 
Sexual species of Endo- Ix Ix Ix Ix | Fees, Ix— Ix ete. 
gone. Mycelium and gametangia zygote | spores, mycelium. 
Parthenogenetic species { Ix— Ix— Ix— 1x 2 1x Ix— Ix etc. 
of Endogone. il Mycelium and gametangium | azygote | spores, mycelium. 
As sporulating organs the zygote and azygote (or germ sporangium 
of the same) of Endogone are homologous structures. The true asexual 
sporangium has been eliminated. Likewise, in the protoascomycetes, 
where the threshold from the phycomycetes has been crossed, the 
zygote (‘‘germ sporangium,”’ a generalized ascus) of Dipodascus, and 
the azygote (‘‘germ sporangium,”’ “‘generalized ascus’’) of Ascoidea, 
as sporulating organs are homologous structures. Ascoidea is prob- 
ably parthenogenetic, the ‘‘generalized ascus’’ being a transformed 
gametangium. Free cell sporulation occurs in both genera. This 
interpretation of the relation of the free cell sporulating organs of 
Dipodascus and Ascoidea is supported by the situation in Eremascus 
fertilis and Endomyces magnusii where the ascus is in some cases of 
sexual origin, in others of parthenogenetic origin, a single gametange 
becoming the ascus. ndogone, with several sexual species having 
sexually produced sporulating organs (zygotes), and other species 
with parthenogenetically produced sporulating organs (azygotes), is 
interesting in that it illustrates the homology of these structures, and 
suggests how the parthenogenetic sporulating organs (generalized 
asci) of Ascoidea, Protomyces, etc., may have arisen. It is interesting 
