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

12 MARCUS M. HARTOG.
Chlamydomonas pulvisculus, with oogamy in the Peronosporese,
and in Gymnosperms and Flowering Plants.
IV. COMPARATIVE GAMETOGENY IN THE VEGETABLE
KINGDOM. 1
I propose now to examine, as completely as materials will
allow, the types of the modes in which gametes are differentiated
in the vegetable kingdom, from the Protophytes
upwards. I have not followed any published classification;
nor have I aimed at absolute completeness in examples, but
only in types.
A. PROTOPHYTES AND CELLULAR ALGJE.
Many of the lower types have been treated incidentally in
the foregoing section, and I need not revert to them. In
CH^TOPHORACEJE and ULVACE^; the zoospores are frequently
4-flagellate, the isogametes 2-flagellate. This would seem to
indicate that the segmentation which would otherwise have
formed zoospores has been pushed a stage further in the formation
of gametes, i. e. that the gametes are formed by the
bipartition of the nascent zoospores. Multiple union is not
rare in this group. In several members the conjugation of
what are supposed to be gametes has not been observed, but
their nature is a matter of inference from comparison with
allied forms ; possibly these doubtful gametes are exogamous,
and could find no suitable mates in the specimens under
observation.
To ULOTHRIX I have referred above (p. 9). The formation
of zoospores and gametes is peculiar : the nuclear divisions are
completed before the cytoplasm divides; the vacuole becomes
excentric and peripheral, surrounded by a layer of cytoplasm
which takes no share in the divisions of the rest of the proto-
1
I have not confined myself strictly to gametogeny, but have described
the formation and fate of the zygote wherever it was necessary for the elucidation
of the true character of the gametes.