A p io c y stis Bxaunia.na. Nag. Einz. Alg. p. 69.
Thallus pear-shaped, pallid green, the cavity filled up by
gelatinous matter, in which are imbedded the gonidia, at first
few, increasing in number with age, as far as 1600.
S i z e . Frond -0 4 -'l mm. high, gonidia -012 mm. diam.,
cells -OOTS-'Oll mm. (Rabh.).
Rabh. Alg. iii. 43. Frcsen. Beitr. p. 237, t. ii. f. 1-20.
Henfrey in Micro. Journ., 1856, p. 52, t. 4, f. 26-27.
Fresh water ditches, &c.
Professor Henfrey fonnd this plant in January, in a jar of water containing
aquatic plants brought from Wimbledon Common six months
previously. The development, as recorded by Nageli, is detailed in the
article quoted above.
“ The young ‘ swarm cells’ (zoospores) attach themselves by their
ciliated point (especially to Cladophora fracta), and become invested
with a club-shaped, enveloping membrane. The first division of the
green body then takes place in the direction of the axis of the vesicular
envelope, and is repeated alternately in each direction of space. Dnring
this the vesicle in which the cells (gonidia) lie, continually expands, and
generally becomes very evidently pedunculated. Toung vesicles
contain a regular number of cells, namely, 2, 4, 8, 16, 32, &.O., but the
number afterwards becomes indefinite ; in largish vesicles, 1-50''
(•5 mm.) long and 1-120" (-22 mm.) diam. I have counted about 300 ;
in the largest, about 1.25" (-1 mm.) long and 1-50" (’5 mm.) thick, some
1,600 cells.
“ The cells (gonidia) are at first uniformly distributed over the whole
cavity of the vesicle. Subsequently they generally become collected on
the internal surface of the wall of the vesicle, where they lie in one or
more strata. Bnt the cell division always takes place in all directions
of space, the cells situated internally advancing ontwards towards the
periphery. In old vesicles the cells are sometimes arranged in rings
of eight npon the wall. When the family of cells is mature for
‘ swarming,’ which may occur at very different sizes and with very
different numbers of gonidia, the cells begin to move, at first slowly,
from their places, and then gradually to circulate more rapidly in and
out about each other ; the vesicle bursts, and the gonidia emerge by the
orifice which is formed. Sometimes the swarming is preceded by the
state in which the cells are arranged in parietal rings.
“ The cells secrete an abundant gelatinous coating, which becomes
softened within the vesicle, and confluent into a structureless jelly. The
vesicle sometimes appears merely as the boundary line of the je lly ; in
general, however, it may be distinguished as a distinct wall composed of
denser gelatinous substance, the internal outline of which is always
distinct and sharp, while the outer is frequently indistinct, and partly
dissolved.”—Nageli. ■
Plate VII. fig. 1. a, young frond ; h and c, older fronds x 100
diam.; d, frond with cells undergoing segmentation X 200; e, part of
frond with mature gonidia X 400; / , free gonidia; g. ciliated gonidia or
zoospores X 400 diam.
Inoderma lamellosum, Kutz., has been said to have occurred in
Britain, but we have not been able to satisfy ourselves of its occurrence.
G en u s 13. RHAFKIDIVBI. Kwt%. (1845.)
Cells fusiform, or cylindrical, generally very gradually cuspidate
or acuminate at the ends, rarely obtuse, straight or
variously curved, single, geminate, or fasoioulately aggregate,
decussate in the centre, or radiately conjoined, rarely two
laterally united at the end, other cells free. Tegument thin,
smooth. Contents green, very finely granular, furnished with a
central, or rarely lateral, transparent vacuole. Division of the
cells only in one direction.
B h ap h id ium aciculaxe. Braun. Rabh. Exs. 112.
Yery slender, 15-20 times as long as broad, yellow-green,
often single, acioular, acutely cuspidate at each end, straight, or
sliglitly curved or somewhat lunate.
Ankistrodesmus acutissimus, Archer in Micr. Jo urn., 1862, t.
xii. f. 44-56.
Closterium Griffithii, Berk. Ann. Nat. Hist. xiii. 256, t. 14,
f- 2.
Bhaphidium polymorphmn var. y aci'c«(ar«, Eabh. Alg. iii. 45.
In pools.
“ Cells very minute, 20-25 times longer than broad, fusiform, very
slender, straight, very acutely acioular, solitary or forming fasciculi of
2-4 cells ; endochrome light-green, mostly with a minute parietal semicircular
or rounded pale body or space placed near the middle of the
cell, otherwise usually appearing homogenous, sometimes slightly
granular.” I t agrees with R. falcatmn in its very slender and acute
cells, but it differs from it by its straight, not arcuate cells, by its fusiform
more quickly attenuated cells, by its more intensely acute extremities,
and by the constituent cells of an old fasoioulus being much fewer
in number.—Archer.
Plate V III. fig. 3. Cells magnified 400 diam.
B h ap h id ium fa lc a tum . (Coi'da.)
Fusiform, slender, acutely cuspidate at each extremity,
carved, or semi-lunar, 4-16 congregated in fascicles.
Micrasterias falcata, Corda Aim. Carls. 1885, p. 121, t. 2,
f. 29.
Staurastrum falcatum, Ehr. Weigm. Arch, 1836, p. 185.
Closterium falcatum, Meneg. Liunaja, 1840, p. 233.
Ankistrodesmus gregarius, Breb. in litt.
Ankistrodesmus falcatus, Ralfs Desm. t. 34, f. 3.
Rhaphidium polymorphum, var. c. falcatum, Rabh. Alg. iii, 45.
In pools.
I t is a very common plant in ponds, &c., and resembles a minute
young Closterium, except that although some individuals may be solitary,
others will be seen in the same gathering collected in the characteristic
fascicles.
Plate V III. fig. 4. a, families magnified 400 ; b, magnified 800 diam.