The process of spore formation just described, it will be seen, is entirely
non-sexual, being simply a vegetative process, analogous to the budding of
higher plants, and the fission of some of the lower plants and animals.
_Vaucheria_ has, however, a second and far higher mode of reproduction,
viz., by means of fertilized cells, the true oospores, which, lying dormant
as resting spores during the winter, are endowed with new life by the
rejuvenating influences of spring. Their formation may be briefly described
as follows:
When _Vaucheria_ has reached the proper stage in its life cycle, slight
swellings appear here and there on the sides of the filament. Each of these
slowly develops into a shape resembling a strongly curved horn. This
becomes the organ termed the _antheridium_, from its analogy in function to
the anther of flowering plants. While this is in process of growth,
peculiar oval capsules or sporangia (usually 2 to 5 in number) are formed
in close proximity to the antheridium. In some species both these organs
are sessile on the main filament, in others they appear on a short pedicel
(Figs. 3 and 4). The upper part of the antheridium becomes separated from
the parent stem by a septum, and its contents are converted into ciliated
motile antherozoids. The adjacent sporangia also become cut off by septa,
and the investing membrane, when mature, opens: it a beak-like
prolongation, thus permitting the inclosed densely congregated green
granules to be penetrated by the antherozoids which swarm from the
antheridium at the same time. After being thus fertilized the contents of
the sporangium acquire a peculiar oily appearance, of a beautiful emerald
color, an exceedingly tough but transparent envelope is secreted, and thus
is constituted the fully developed oospore, the beginner of a new
generation of the plant. After the production of this oospore the parent
filament gradually loses its vitality and slowly decays.
The spore being thus liberated, sinks to the bottom. Its brilliant hue has
faded and changed to a reddish brown, but after a rest of about three
months (according to Pringsheim, who seems to be the only one who has ever
followed the process of oospore formation entirely through), the spore
suddenly assumes its original vivid hue and germinates into a young
_Vaucheria_.