f
82 ZVGOPHYOEÆ.
rent. Indeed, having sent specimens to several celebrated algologists,
they hesitated to admit it into Tyndaridea, until Mr. Hassall, who also
at first strongly doubted whether it belonged to the Conjugatoe, fortunately
gathered fertile specimens. Snob we ourselves fonnd shortly
afterwards, and we have since repeatedly met with them ; the appearance
of the plant in conjugation, however, is so altered that its identity
can only be determined by tracing it through all its changes.
“ In its usual state the sheath is very conspicuous, and the dense endochrome
so fills the cells that the plant looks like a Conferva, the continuity
being interrupted merely at the dissepiments. When about to
conjugate the sheath has nearly or altogether disappeared, and the endochrome
is collected into two stellæ, leaving the rest of the cell oolonr-
less.”—Ralfs-
Hassall also found and examined the plant, and figured it with zygospores
in the cells of the filaments, whereas the Continental species,
since the figure by Kutzing, is always described as having the zygospore
in the canal of conjugation. There cannot, therefore, be the slightest
doubt that the species fonnd by Hassall and Ralfs is quite distinot from
that known to Kutzing, Rabenhorst, and De Bary. Priority certainly is
in favour of Hassall’s name, and it is the Continental species which must
give way, and yield up a name, acquired in error, to its rightful claimant.
Our figures are based on the sketches and drawings by Ealfs, with
whom we have been in communication on this question. I t is absurd to
suppose that Ealfs and Hassall were both deceived, as well as Mr,
Jenner (an admirable observer), to whom the species was undoubtedly
known, and finally Mr. Salter in preparing the drawings from the
specimens for the “ English Botany.” Unfortunately we could find no
fruit in the specimens which we possess, collected by Ralfs forty years
ago, nor could we obtain specimens in conjugation from Cornwall during
the past spring.
Plate X X X I . jig. 1. a, h, portions of sterile threads X 400 ; c,
fertile cells with zygospores X 400, after Ealfs ; d, conjugating cells X
400.
If:;'
Zygnema le io sp e im um . De Bary. Babh. Algm Exs. No. 638.
Sterile cells equal in length and breadth, or sometimes twice
as long.
Zygospore globose or broadly oval, formed in one of two
conjugating cells ; membrane brown, even.
Sporiferous cells a little swollen.
S iz e . Cells -022 mm. diam. Zygospore -023--03 mm.
De Bary Conj. p. 7 7 ,1 .1, f. 7-14. Rabh. Alg. iii. 249. Kirsob.
Alg. Schl. p. 125.
In ditches filled after rain.
The two British species with the membrane of the zygospore even,
in this section, are the present and the following, which will require
some care in the discrimination. The inflated cells, which enclose the
zygospores, in the present, is relied upon as one of the features which
distinguish it from the succeeding species, as well as the larger size of
the zygospores.
Plate XXXI. jig. 2. a, portion of fertile thread X 400; b, c,
fertile cells, with zygospores, after De Bary X 400; d, mature zygospore
X 400, after DeBary.
ID
Zygnema in s ig n e . Kutz. Tab. v. t. 17, f . 1.
Sterile cells equal, or twice as long as broad.
Copulation soalariform or lateral ; zygospore globose or
slightly oval; membrane brown, even.
S iz e . Cells '026-’03 mm. diam.; zygospore about '026 x
•032 mm., or globose about -03 mm. diam.
De Bary Conj. p. 78, t. 8, f. 14-16. Rabh. Alg. iii. 249.
Kutz. Tab. V. t. 17, f. 1. Kirsch. Alg. Schl. p. 125.
Tyndaridea insignis, Hass. Alg. p. 163, t. 38, f. 6, 7. Jenner
PL Tunb. Wells 182.
Zygnema tenue, Rabh. Exs. No. 674.
In streams and ditches.
The cells of this species at the time of ooiij ngation are apt to become
much distorted, inflated sometimes on one side, sometimes on the other,
and even to conjugate in the manner represented by DeBary, and copied
on onr plate.
Plate XXXI. fig. 3. a, sterile cells X 400; b, fertile cells with
zygospores X 200 ; c, fertile cells, with longitudinal conjugation, X 200,
after De Bary ; d, zygospore X 400.
G en u s 45. S F 1R 0 6V R A . Link. (1820.)
Cells with one to several parietal chlorophyll bands, usually
spirally winding to the right. Copulation ladder-like {Spirogyra)
or lateral {Rhynchonema). Zygospores always within the
wall of one of tbe united cells. Copulating cells similar to tbe
sterile ones, or swollen out.
This genus, as now accepted, includes two genera as recognised by
Kutzing, Spirogyra and Rhynchonema. In the former the conjugation
was soalariform, and in the latter it was lateral. I t is now found that
in many species, probably in all, both kinds of conjugation take place,
according to circumstances. The same filament, which in some portion
of its length conjugates with a neighbouring filament, bas also been
observed conjugating laterally between two of its own cells. The genus
Rhynchonema therefore has thus been proved to represent only one of
the modes of conjugation of the same plant, which under other conditions
conjugates with a neighbouring filament.
In past times too great importance was attached to the breadth and
length of the cells in the sterile filaments, and also to the character of the
spiral bands, features which are now known to be too variable to be relied
upon, the most important and reliable characters being derived from tbe
zygospore ; hence only specimens in fructification can be accurately
determined.
The most recent work on the species of Western Europe is a Monograph
of Spirogyra, as represented in France, by Mons. Paul Petit.
(Paris, 1880.) See also Professor Cleve’s “ Monograph of tbe Zygnemaceæ.”