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

SOME PROBLEMS OF REPRODUCTION. 23
plasm; a small portion of granular protoplasm carries down a
single male nucleus to fuse with the female one. The gonoplasm
secretes an inner coat to the zygote, around which an
outer one or "epispore" is secreted by the periplasm. The
nuclei present in this layer can hardly be essential to the formation
of the epispore, since no nuclei are present in the
layer of epiplasm which does similar service to the endogenous
spores of the Ascomycetes. We can only regard the nuclear
divisions in " oogonium" and antheridium as phylogenetic
reminiscences of the formation of gametes by cell division;
the periplasm is thus equivalent to a number of degenerated
gametes which have taken on the function of epispore formation;
the multitude of gametes are sacrificed to the few.
Obviously what we here term the " oogonium" is neither
morphologically nor physiologically the exact equivalent of a
single oogonium in cellular, as distinguished from apocytial
plants, but represents an apocytium of oogonial cells; and the
antheridium has a similar relation to the spermatogonium of
cellular plants.
The processes in those SAPROLEGNIEJE 1 that have been fully
studied mark a distinct step further in the same path. The
oangia are at first filled with multinucleated protoplasm ;
vacuoles appearing and enlarging bring the nuclei closer
together, and they soon fuse in pairs, a process continued
until their number is materially reduced j while the mitoses
observed in Peronospora do not take place. The primitive
nuclei are vesicles with a central chromatin mass supported
by a "linin" or nucleo-hyaloplasma network. In fnsion of
the nuclei the chromatin masses long remain distinct, but
are smaller and take up stain less readily, and the nuclear
wall at this stage ceases to stain, so that the fusion nuclei
have the look of vacuoles in the cytoplasm containing a
variable number of chromatic granules. During this stage
the true vacuoles unite to form a large central cavity into
which fresh vacuoles open, so that the protoplasm forms a thick
1
The following account is largely taken from an original paper of my own
" On the Cytology of Saprolegnieee," still incomplete and unpublished.