Some Problems of Reproduction: a Comparative Study of ...

22 MARCUS M. HABTOG.
The last two genera have a mycelium unusually well developed
for this group, and are regarded by De Bary as doubtful
members thereof.
MQNOBLEPHARIS 1 forms its spermatozoa by the resolution
of the protoplasm of spermatangia into one-flagellate cells,
differing only in their smaller size from the vegetative zoospores,
and therefore possibly formed by bipartition of potential
zoospores. The protoplasm of the oangium, after forming a
terminal aperture, contracts and rounds off into the oosphere;
which, if uninucleate, has probably, from its size, formed its
gametonucleus by the fusion of many vegetative nuclei. No
epiplasm is apparently formed.
The PERONOSPOREJE are oogamous and siphonogamous.
The only species in which the formation and union of the
gametes has been fully studied is Peronospora parasiticaj
and I shall utilise Wager's careful description 2 of the sexual
processes in this species, having had the opportunity of verifying
its accuracy on the original specimens. The spherical
" oogonium " (or rather oangium) is cut off from the tubular
hypha by a basal septum if terminal, by two if intercalar;
it is apocytial, containing numerous nuclei. Each nucleus
undergoes repeated bipartition; and the majority of the nuclei
so formed pass into a peripheral layer of protoplasm, thus
constituting the so-called " periplasm ;" three of them pass to
the middle of the central mass of protoplasm, the so-called
" gonoplasm/' and fuse therein into the single pronucleus.
The " antheridium " (or spermatangium) is an ovoid enlargement
of a hypha, closely applied by its apex to the oogonial
wall and cut off by a basal septum ; it contains several nuclei,
which like those of the " oangium " multiply by mitosis; it
emits a tube which perforates the oogonial wall and passes
through the periplasm to open just at the surface of the gono-
1
Cornu, " Monographie des Saprolegnie'es," in ' Ann. Soi. Nat. Bot.,'
ser. 5, vol. xv.
2
"On the Structure of the Nuclei in Feronospora parasitica," in
1
Annals of Botany," vol. iv (1889).