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F a m i l y V. OEDOGONIACEÆ.
Monoecious, or dioecious algæ. Filaments articulated, either
simple (OEdogonium) or branched (Bulbochoeie). Basai cell
obovate-clavate, mostly lobately divided, or ending in a dise.
Propagation by zoospores, or by oospores after sexual fecundation.
The zoospores formed singly in certain cells, broadly oval
or globose, transparent at one end, and furnished with a crown
of vibratile cilia. Oogonia single or in a chain (2 to 5) contiguous
to each other, more or less tumid, with a single oospore
in each, becoming reddish brow'n or yellowish when mature,
and then, before germination, dividing into (mostly 4)
zoospores.
Male plants, dwarf (nannandrous) and attached to the female
plants, or elongated (maorandrous) and similar to the female
filaments (often rather thinner). Spermatozoids produced in
abbreviated special cells (spermogonia).
G en u s 64. (EDOGONIUia. Linie. (1820.)
Articulated filament simple, at first fixed, afterwards free
swimming. Cells marked with transverse striæ at one or other
extremity. Terminal cell sometimes elongated and setiform.
Eith e r monoecious or dioecious ; when dioecious th e male plants
either dwarf—produced from short cells of the female plants—
or elongated and independent.
Propagation by asexual zoospores, and by oospores sexually
fertilized.
For details of the etrnotnre and reproduction, consult “ Braun on
Eejuvenescence” (Kay Society, 1853). “ Pringsheim Jahrbücher”
(1857). “ Quarterly Journal of Microscopical Science,” vi. new series,
1866, p. 149. DeBary, “ Afdogonium und Bulbochæte” (1854). Juranyi
in Pringsheim “ Jahrbücher ” (1873). Carter, in “ Annals of Natural
History,” 3 ser. i, p. 31. Taupell, “ Jagttagelser ov. betrugt. OEdogo-
nium” (1859). Wood, “ Fresh Water Algæ of the United States ” (1872).
Wittrock, “ Prodromne Monographiæ OEdogoniearnm ” (1874).
The sterile filaments of OEdogonium resemble those of C< nferva at a
casual glance, but are soon seen to be distinguished by transverse parallel
striæ at one or other extremity of many of the cells. These striæ are
indications of the mode of cell increase (PI. LVII, fig. 5) which takes
place in the following manner ;—When a cell has reached maturity, and
is about to divide, a little circular line is seen near its upper end.
Gradually the line widens, and it is seen that the wall of the mother
cell has divided all round, and the cell above is slowly raised by the
growth of the daughter cell, arising, as it were, out of the apex of its
parent cell, and carrying upwards the first streak or cap left by the
ill
breaking away of the wall of the mother cell. In this manner the new
cell soon attains a length equal to the on© from whence it sprang (the
successive stages shown on Plate LVII, figs. 1 to 4). When th© young
cell has matured it becomes in turn a mother cell, the splitting round is
repeated, a second streak or cap is carried upwards, and thus as many as
four, five, or six successive cells are formed, as indicated by the four,
five, or six striæ or caps which may be counted at the apex of a cell. The
number of caps corresponding to th© number of cells produced in this
manner consecutively immediately beneath the caps.
Asexual reproduction takes place by the formation of a single zoospore
in one of the cells of the filament (Plate LVII, fig. 15). I t is of a globose
or somewhat ovate form, furnished near its apex with vibratile cilia (fig.
14). When mature it escapes by rupture or fissure of the mother cell,
moves about for awhile, then becomes attached by the ciliated end, and
ultimately developes into a young plant.
Sexual reproduction is varied in three ways. In the monoecious species
th© oogonium is an inflated cell, more or less globose, enclosing a single
oospore of similar form. The oogonium is either perforated by a pore,
or splits round and opens with a lid or operculum. The same thread
bears above or below the oogonium very much shortened cells, in which
on© or two active spermatozoids are produced. These escape when
mature, and fecundate the oospore through the perforation or opening of
the oogonium, after which they disappear, and the oospore ripens into a
perfect, fertile, resting spore.
In the dioecious species there are two modes of sexual reproduction.
In one group of species the males are dwarf, almost might be called
antheridia. The oogonia and oospores are the same as in the monoecious
species. In like manner there are also abbreviated cells in some otber
part of the same thread, but these do not produce spermatozoids, but
androspores, small active ciliated bodies, which move about for a time,
and then attach themselves either upon or near the oogonia, grow into
the form of an inverted flask (figs. 8 to 10 ), being supported by a more or
less elongated stem, and constitute the dwarf male (nannandrous) plants,
the cells at the apex of which contain the spermatozoids, the upper cell
opening by a lid, or cap, to permit of the escape of its contents, which
fertilize the oospore as in the previous method.
The second group of dioecious species have male filaments, which in
all respects resemble the sterile females, except that they are usually a
little thinner. The female filaments produce only the oogonia.
The male filaments, in certain abbreviated cells, give origin
to the spermatozoids, which in due time escape and fertilize the
oospores of the female plants. Thus, in the first group, the dwarf males
are generated in certain privileged cells of the female plants, whilst in
the second group the male and female filaments are from the first distinct.
The former are called nannandrous species, the latter macron-
drous.
The fertilized oospore becomes a resting spore, which ultimately
passes through the following stages :—Previous to germination the spore
has an egg-shaped figure ; the cell contents are densely crowded, and
composed of minute brownish-green granules, closely surrounded by a
distinct cell-membrane. Outside this membrane there is found besides
quite a distinct cell-membrane. Upon germination there are formed in
both membranes slit-like openings, wherenpon the cell contents emerge,
surrounded by an extremely delicate hyaline covering. The cell contents
are composed not of one, but usually of four green masses, each surrounded
by its cell-membrane. Sometimes also as it appears, abnormally,
the masses are two or three in number. Thé four cells which
P roceed from germination possess an oval form, and their cell-membrane
is hyaline. After the contents of the spore have emerged there remains
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