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

24 MARCUS M. HARTOG.
mantle around the central space. The protoplasm then becomes
aggregated into distinct masses, the oospore " origins/' projecting
into the vacuole and united by a continuous peripheral
mantle, which thins gradually as its substance becomes taken
up into these masses. Finally, the connecting mantle gives
way; the masses separate and round off; after a short rest
they become amoeboid, and some of their blunt, non-nucleated
processes become abstricted. Very soon, however, they are
taken up again by the masses which abstricted them, and
these masses round off into the " oospores." The very same
abstriction and resumption of non-nucleated processes of cytoplasm
takes place in the formation of the asexual zoospores ; x
it is probably a process derived from cell-wall formation,
analogous to what we have seen in Cladophora, but in a
yet more reduced condition. The oospores after coming to
rest soon become surrounded by a cellulose wall, thickened by
successive internal deposits; each finally possesses a single
nucleus in the resting state, i. e. spherical, with a single
central sphere of chromatin. The complete fusion of the
nuclei takes place in Saprolegnia as early as the first formation
of the masses or oospore origins, while in Achlya it may
be deferred till after the formation of the spore membrane,
for young oospores are frequently binucleate.
The antheridiutn is also multinucleate, and lies closely
appressed to the oogonium; on the rupture of the protoplastic
mantle of the oogonium and separation of the oospores
it emits tubes which grow into the cavity of the oogonium,
and abut against the oospores just before they form a cell-wall
or during this process; but they do not enter the oospore,
open, or emit any fertilising bodies. 3 Their contents are
1 See Rothert, "Entwioklung d. Sporangien bei den Saprolegnieen,"
1888 (this paper was an advance publication of ' Cohn's Beitrage,' vol. v,
1890; it was abstracted and criticised by me under the title " Recent Researches
on the Saprolegniese," in ' Annals of Bot.,' vol. ii, 1888.
3 I have now fully satisfied myself that the contrary statements of Pringsheim
(in ' Sitzungsber. d. Berl. Akad.,' 1882) are erroneous, being based
partly on the intrusion of parasites as shown by Zopf, partly on the postmortem
appearances produced by unsuitable reagents.