232 Barker . — The Morphology and Development of 
originated by similar means. It has been already mentioned 
that the periplasm of oogonia probably represents the sexually 
functionless elements of a gametangium that was originally 
completely fertile. Assuming the origin of the ascus from the 
zoosporangium, the sterile nuclei have either disappeared or 
are represented by the two nuclei which are formed at the 
same time as those which fuse in the young ascus, one of 
which is cut off into the terminal cell of the ascogenous hypha 
and the other into a cell immediately beneath the penultimate 
ascus. The latter appears to be the most likely alternative, 
in which case the periplasm of the ascus represents a portion 
of the non-sporogenous protoplasm which has escaped being 
cut off into the sterile cells with the sterile nuclei. 
The other reproductive organs of the Oomycetes and the 
Ascomycetes are in many cases clearly homologous. The 
conidia of the latter undoubtedly correspond to those of the 
Peronosporaceae, in which order many examples are presented 
of the transition from the zoosporangial to the conidial con- 
dition. 
In the above comparisons only those Ascomycetes which 
possess a functional archicarp have been considered. It is, 
however, generally admitted by most botanists, with the 
exception of Dangeard, that the other members of that group 
are to be looked upon as sexually degenerate, and are there- 
fore considered as having originated from sexual ancestors. 
Summarizing, Albugo , Pyronemct , and Monascus possess a 
very characteristic and probably primitive method of multiple 
fertilization. The germination of the fertilized egg in both 
groups shows gradations between a direct division into spores, 
e. g. Albugo and Dipodascus , and a comparatively highly 
evolved differentiation into sterile and sporogenous structures, 
e. g. Phytophthora omnivor a and Pyronema. 
Combining these characters, the ancestral form of the 
Oomycetes was probably an organism possessing the method 
of multiple fertilization, the compound egg of which gave rise 
to numerous spores only by division, i. e. the species Albugo 
Bliti and A. Portulacae represent in those characters the 
