M
P a n d o z in a m o zum . Eh-, Inf. p . 53, t. ii. f. 33.
Cænobium globose. Cells green, 16-32, arranged about the
periphery. In the forms which produce the resting spores, the
cells are crowded together in the centre. Resting spores after
becoming encysted bright red.
S iz e . Cænobium -2 mm. Cells -01--015 ram. diam.
Eabh. Alg. Eur. iii. 99. Henfrey Micr. Trans. (1856) p.
49, t. 4. Pringsheim Monatsb. Berlin, Oct., 1869. Ann.
Nat. Hist. v. (1870) p. 272. Pritchard Infus. pp. 157 and 517,
t. xix. fig. 59-69. Braun Eejuv. pp. 169-209. '
In standing water.
“ Fronds hyaline from about 1-80" downwards. Gonidia either 16,
and then arranged in four circles of 4, or 32 and then in five circles, two
at the poles of 4, and the intermediate three of 8 gonidia, which in the
perfect form stand near the periphery, and wide apart. In the forma
which produce the resting spores the gonidia are crowded together in
the centre. The gonidia are green, but the contents of the resting
spores, after they have become encysted, are converted into oily and
granular matter of a bright red colour.”—Henfrey.
Pringsheim, in his memoir “ on the pairing of Zoospores,”* makes
special reference to this species. He says that asexual reproduction
takes place in Pandorina, as in other multicellular Volvocineæ, by the
formation of a perfect young plant in each cell of the mother plant. By
the gradual dissolution of the general envelope and of the special membrane
of the mother-cells, the young plants become free, and escape. In
sexual reproduction, as in the asexual, the membrane of the old plant
swells, and sixteen yonng plants are formed. The young plants, however,
are (at least iu part) not neuter, but sexual, and either male or
female. iVhether the mother plant is monoecious or dioecious is difficult to
determine, because the male and female plants are externally alike, and
can hardly be distinguished with certainty during copulation. There is
no striking difference in structure between the sexual and asexual
plants, although, amongst the former, plants with less than sixteen cells,
especially with eight cells, are oftener produced. Moreover, the dissolution
of the membraue of the mother-cell proceeds more slowly than in
the case of neuter plants, one result of which is that the young asexual
plants vary much in the extent of their growth, and continue united in
groups of different sizes for a long time after their formation, according
as a greater or less number of them have happened to become free from
the gelatinous mass in which they were embedded.
As the individual groups are at first motionless, and the mother plant
loses its cilia during the formation of the young ones, the entire group
is at first entirely quiescent. Bnt afterwards the young sexual plants,
like the neuter ones, produce upon each of their cells two cilia, which
commence their motion as soon as the enveloping mucus admits of it,
and thus ultimately the entire group assumes a state of active rotation.
During the rotation of the groups the same process of expansion
and dissolution takes place iu the membrane of the sexual plants
as occurred in the mother plant ; but the contents of the cells of the
sexual plants do not undergo division, but combine to form a single
zoospore, which becomes free by the rapid dissolution of the membranes.
In their general structure these zoospores differ in no way
* Monatshericht, Roy. Acad. Sciences, Berlin, Oct.. 1869. Translated
in “ Annals of Natural History,” Vol. V. (1870), p. 272.
I;'; ill
from other zoospores. At their colourless apex they exhibit, like
other zoospores, a red body placed on one side of the apex, and two
long vibrating cilia, by which they move in the manner common to
zoospores. The individual zoospores exhibit no marked differences,
except that they vary in size within tolerably wide limits, but not in a
manner to indicate the existence of two different sorts.
Amongst the groups of isolated zoospores of different sizes some are
at last seen to approach one another in pairs. They come into
contact at their anterior hyaline apex, coalesce with one another, and
assume a shape resembling a figure of 8. The constriction which
marks their original separation disappears by degrees ; and the paired
zoospores form at last a single large green globe, showing at the circumference
no trace of their original separation. It may be seen,
however, that the globe is larger than the individual neighbouring zoo-
spores, that it has a strikingly enlarged colourless mouth spot, with
two red bodies on the right and left, and that it is furnished with four
vibrating cilia originating in pairs near the two red spots. The four
cilia, however, soon become motionless, and together with the red spots
disappear.
This act of conjugation occupies some minutes from the first contact
of the zoospores to the formation of the green globe. The latter
becomes the oospore, which, after growing slightly larger, and assuming
a red colour, germinates after a long period of rest, and brings forth a
new Pandorina. There is hardly any appreciable difference, except in
size, between the male and female zoospores. Most frequently a small
zoospore pairs with a larger one ; but two of equal size often unite.
Probably both the females and the males vary much in size, the former
more so than the latter.
With regard to the entire plants from which the zoospores are produced,
there is little doubt that those of the largest size are females ;
but the sex of the smaller and middle-sized ones cannot be determined
with any certainty. The germination of the oospore is like that of other
YolvocinecB, especially resembling in its early stage the germination of
the resting spores produced by the microgonidia of Hydrodictyon utri-
culatum. The oospore bursts, and produces a single large zoospore (m
rare cases two or even three), which divides into sixteen cells, and
becomes a young Pando7'ina.
Plate X X V II. fig-2i. Pandorina morum—a, a very small family; h,
c, sixteen-celled families ; d, eight-celled family ; e, solitary cell ; /, the
same, further magnified, showing process of subdivision; 32-celled
family ; h, small family undergoing division ; i, 16-celled family
divided into sixteen daughter families. All after Stein X about 500.
G e n u s 43. GONIUM. MülUr. (1873.)
Cænobinm quadrangular, tabular, angles rounded, formed
from a single flat stratum of cells, g irt by a broad hyaline
plano-convex tegument. Cells 16 (central 4, peripherical 12J,
polygonal, bright green, becoming with age disordered, granulose,
connected by the produced angles, chlorophyllose vesicle
central, furnished with colourless contractile vacuoles, and two
long exserted cilia.
Propagation by repeated division of the cytioplasm.
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