ift
II
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spore; nevertheless we have not followed Wittrock in uniting Mou-
geotia, Mesocarpus, Plem'ospei-mum, Craterospermum, and Stauros-
pefrmum under the one genus, Mougeotia,, because we think that there
are sufficient characters to warrant the retention of Staui'ospermum
apart from Mesocarpus. If the mode of development in the following
two species is accurately appreciated, this genus is more allied to Zyqo-
goniuin than Mesocarpus. See Archer in Quart. Micro. Journ., l*8i)6,
p. 271.
Mougeotia g lyptosperiua. DeBary Conj. p. 78, t. 8, / . 20-25.
Sterile cells 7 to 12 times as long as broad.
Zygospores large, ova], with a thick, firm, yellow-brown
epispore.
Sporiferous cells elongated.
S iz e . Cells ‘Ol-'OIS mm. 6 to 10 times as long. Zygospore
-Oiex-OSS mm.
Eabh. Alg. Eur. iii. 255. Archer in Quart. Journ. Micr.
Sci. 18G6, p. 65.
As pointed out by Mr. Archer (loo. cit.) “ this plant is not truly a
Mesocarpus, but in its mode of conjugation more nearly approaches
certain Zygnemata. I t is no doubt related, on the one hand to Mesocarpus
(Hass.) ; like it the endochrome forms a compressed longitudinal
band, and like it too, tbe zygospore is formed half-way between the two
conjugating joints. But, it is distinguished strongly by the fact that
here the whole cell contents ‘primordial utric le s’ and all, of the two
conjugating joints completely coalesce, leaving the old oell-walls empty,
in order to form the zygospore; whilst in Mesocarpus the contact of the
primordial utricles of the two oonjugating cells is not followed by a
complete coalescence of the two into the zygospore ; but by a concentration
of the principal part of the green and solid contents in the connecting
canal half-w'ay between the two joints, and the shutting off
thereupon of the residue of the pale granular contents remaining in each
parent joint, the denser central portion becoming tbe spore, and that
cut off on each side eventually becoming effete and lost. Hence in
Mougeotia glyptosperma the spore is the actual result of the complete
fusion of the entire cell contents of the two conjngating joints—it is
the true zygospore ; whilst in Mesocarpus the ultimate spore is a
danghter.cell, as it were, of the zygospore. Therefore, on the other
hand, the present plant shows an affinity to Zygnema; but it is, of
course, completely distinct in the flattened band of endochrome, not
doubly stellate, as in that genus, not to speak of the extremely different
comparative length of the cells, which, within the limits of each is
constant.” ’
Plate XLI. fig. I. a, sterile cells X 400; h, c, conjugatiag cells with
zygospores, after De Bary, X 200 ; d, zygospore, after DeBary, X 400,
M ougeotia laevis. Archer Micr. Journ. 1867 t. 8, / . 1 -3 .
Sterile cells twice as long as broad.
Zygospores broadly elliptic or oval. Epispore thick, brown.
Sporiferous cells sometimes elongated.
S iz e . Cells •02--25 mm. Zygospore about ‘045 x -036 mm.
Eabh. Alg. Enr. iii. 255. Arcber Micr. Journ. 1866, p. 270.'
Zygogonium Iceve, Kutz. Tab. v. t. 13.
In ditches and pools.
H :
Mr. Archer has thus described the present p lan t:—“ Cells short, varying
from nearly quadrate to three or fonr times longer than broad,
according to the interval of time elapsed since division ; the contents
bright herbaceous green, forming an axile compressed band (never separate
stellate chlorophyll bodies as in Zygnema) ; the conjugation taking
place by short wide processes, which, along with the shortness of the cells
or joints, gives the pair of conjugating filaments somewhat the appearance
of a perforated ribbon-like structure ; the total cell contents of each
pair of conjugating joints became massed together into an elliptic zygospore
within the inflated transverse tu b e ; the longer diameter of the
zygospore placed vertically to the length of the filaments j the cavity
occupied thereby nob shut off by any septum from the cavities of the
parent joints. I t was evident that there was no septum separating the
zygospore from the cavities of the parent cells, but it lay freely in the
inflated transverse process, though frequently in contact with its walls
about the middle.”
Flate X L I. fig. 2, a, sterile cells X 400; 6, fertile cells with zygospores
X 200.
Sub-Family 2 . M e so o â r p bæ .
Cells cylindrical, united in threads, with axile plates of
chlorophyll. Zygospore tlie shape of the mother-cells ; not
contracted, separating by three to five partitions into a central
firm-walled resting spore, and two or four lateral decaying
cells.
The method of conjugation and spore-formation in the Mesoccorpce was
not thoroughly understood until it was investigated and explained by
De Bary (“ Conjugaten,” 1858), who first recommended the separation
of the Mesocarpece from the Zyynemeoe, and their recognition as separate
families. His exposition of the conjugation of the Mesocarpece is thus
summarised by Wittrock* in a memoir submitted to the Swedish Academy :
—“ Two cells grow together in the common manner by conjugation outgrowths,
and a resorption of the double septum between the two conjugating
cells takes place. By this a cruciated or H-shaped double cell is
formed, in which at first no other change takes place than that the canal
of conjugation is somewhat widened, and that the chlorophyll-coloured
part of the contents of the double cell moves into the canal of conjugation,
and into the parts of the double cell nearest to the canal. This
cruciated or H-shaped cel), thus formed immediately by the conjugation,
De Bary regards as the zygospore of the Mesocarpece, and gives it the
character of being ‘ not contracted ’ in contrast with the zygospore of
Zygnemece and Desmidiece. This zygospore exists, however, only for a
very short time as such. The above-named moving of the chlorophylla-
oeous bodies (not of the whole protoplasmic mass) into the connecting
canal having been accomplished, the zygospore is divided by two or four
septa into three or five cells, of which one, the central one, is a hypno-
spore, rich in ohlorophyllaceons protoplasm (and later in oil), whilst the
two or four lateral cells, containing no chlorophyllaceous protoplasm, are
sterile, and soon going to die. Thus the Mesocarpece have, according to
De Bary, spores of two kinds, namely (1), zygospores, which are formed
* “ On the Spore-formation of the Mesooarpeæ.” By V. B.1878, Wittrock. Stockholm,
I f