♦ h
20 c o o c o r u y o E Æ .
R haphidium d u p le x . Kutz. Phyc. Oerm.p. 144.
Fusiform, slender, slightly sigmoid, single, or 2, 3, or 4
laterally connected at the poles, otherwise free.
Rhaphidium triplex, Rabh. Krypt. FI. Sax., p. 134.
Scenedesmus duplex, Ralfs Desm. 193, t. 34, f. 17.
Rhaphidium polymorphum var. d. sigmoideum, Rabh. Alg. iii.
p. 45.
In pools (apparently rare).
“ Cells linear-lanceolate ; extremities tapering to a fine point and
carved in opposite directions. The cells closely united, frequently the
frond, consists of only a single pair of cells so connected, but sometimes
of two or even three of these pairs, which, however, are remote from
each other, in this case ; as the connecting mncous is colourless, they
look like distinot plants, and their relation can be detected only by
moving the frond. If kept in water for a few days, the cells separate
from each other.’ —Ralfs.
This description is scarcely accurate, as each cell is a distinot plant.
Plate V III. fig. 5. a, cells magnified 400 ; b, magnified 800 diam.
Genus U . DICTYOSFKÆRIUM. Nag. (1849.)
Cells elliptic, with thick confluent mucous investment, combined
in numbers into free-swimming one-layered hollow-
globular families, one always at the ends of delicate threads
which proceed from the central point of the family, and which
become repeatedly branched towards the periphery ; division at
the commencement of a series of generations in all directions of
space ; afterwards, as regards the middle point of tho aggregate
family, as a rule, alternating only in the two tangental
directions.
Only three described species, all of which have occurred in the British
Isles.
D ic ty o sp hæ iium Ehxenbergianum. Niig. Einz. Alg.p. 73.
Families aggregated in a globular, or broadly elliptical
figure ; cells elliptic, very minute, about one-third as broad as
long.
Bizk. Cells •004--0075 mm. (Æaè/i.), ■004-'007 mm, (Kirch.).
Rabh. Alg. iii. 47. Kirch. Alg. Schl. p. 106.
Amongst Confervæ.
“ This form is very minute, and in suitable places, common, the
families in the aggregate forming a globular, or broadly elliptic, or
sometimes subcubical figure ; the rate of growth of the delicate thread
being equal all round, the cells at the ends of each of its dichotomous
ramifications stand at nearly equal distance from the original centre ;
hence the regular figure of the aggregate family. The individual cells
are elliptic, and very minute.”—A.rcher.
Blate IX . Jig. 1. Families magnified 400 diam. j b, fragment with
cells X 400 diam. j c, variety with spherical cells.
PALMELLACEÆ. 21
D ictyosphse iium len ifo zn ie . Buln, Hedwigia ii. 22.
Families aggregated in an irregular form; cells reniform,
nearly twice as broad as long.
S i z e . Cells •008--009 m m . ( 7 ? a J A . ) , ’OOe-'Ol x •01--02 m m .
(Kirch f .
Rabh. Alg. iii. 47. Rabh. Exs. 789. Archer m Micro,
Journ., 1868, viii. p. 65. Kirch. Alg. Schl. p. 106.
In pools. Near Snowdon, N. Wales.
“ This plant possesses larger families than D. Ehrenbergianum, which
are irregularly shaped, seemingly owing to the development of the
delicate supporting fibre not going.on in the same regular manner as in
the preceding species, and the cells themselves are much larger and
reniform.”—Archer.
Plate IK . fig. 2. a, b, plants magnified 400 diam.; o, portions showing
filament.
Dictyosphaerium c o n stiic tum . Archer {Micr. Journ., 1866,j»._128)
having been afterwards found to produce zygospores (see “ Micro.
Jo u n i.,” 1875, p. 415), has been transferred to the Desmidem
in company with Cosmocladium, to which genus it seems to be
allied.
Cosmocladium S a x on icum , EeBary, is sometimes placed by
authors (as in Rabenhorst’s Algse) in this family. But, as
DeBary demonstrated in “ F lo r a ” (No. 21, 1865), the cells
proceed in the same manner as in Cosmarium, and therefore its
proper place is with the Gonjugatm, as one of the Desmideai.
I t has been found in North Wales.
G en u s 15. HOROTOSPORA. Breb. (1840.)
Thallus tubular, gelatinous, swimming free. Cells oblong,
or oval, green, arranged in simple longitudinal series (families),
either remote from each other, or more or less united at the
poles. Tegument thick, confluent, contained within the broad
gelatinous tube, which is either simple or branched.
* Tubes simple.
Hormospoxa m u ta b ilis. Breb. Mem. Fal. 1840.
Tubes intricate, more or less broad, or parallel and coalescing ;
cells twice as long as broad, broadly rounded at each end ;
tegument very thin.
S iz e. Cells -O ll-'O lf mm,, tube diam. -043 mm. (Rabh.).
Eabh. Alg. iii. 48. Breb. in Ann. des Sol. Nat., 1844, t. i.
f. 2. Kirch. Alg. Schl. p. 108.
In boggy pools. Ireland.
Plate X. fig. 1. a, portion of filament X 300; b, same breaking up
X300.