O r d e r I I . Z Y G 0 P H 7 C E Æ .
Eitlier unicellular or multioellular Algæ, witli terminal vegetation,
and destitute of true ramification. Cells single, or
segregate, or geminate, or united in a series. Cliloropliyll-mass
for the most part distributed in plates, or bands, including one
or more amylaceous granules.
Multiplication by division of the cells in one direction.
Propagation by zygospores resulting from the conjugation of
two cells.
Consult here Dr. A. De Bary’s “ Untersuohungen uber die Familie
der Conjugaten.” Leipzig, 1858.
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F a m i l y I. DESMIDIEÆ.
Unioellular Algæ. Cells for the most p a rt compressed,
single, or segregate, or geminate, or a larger number united in
a band, or filament ; variable in form, usually constricted in the
middle, so as to constitute two symmetrical semi-cells.
This large and interesting family is designedly excluded from the
present work, as it is proposed to treat them separately. As so many
students confine themselves exclusively to this family, this proposal
will doubtless commend itself. The excellent text book by J . Ralfs has
long been the standard for English students, and would be so still but
for its scarcity, and the large number of additions in the interval since
its publication.
I
F a m i l y II. ZYGNEMACEÆ.
Multicellular Algæ. Cells cylindrical, equal at both ends ;
fructiferous cells more or less tumid, or inflated, all closely
conjoined in filamentous families, forming an articulated simple
thread, with a central cytioblast involved in radiating protoplasm.
Cell walls lamellose.
Chlorophyll-mass effused, or of a definite form, often forming
a spiral band.
Vegetation by repeated transverse division.
Propagation by zygospores, resulting from the conjugation of
two cells. Conjugation taking place in three ways, lateral,
soalariform, and genuflexuous.
This family is suh-divided into three sub-families, according to the
character of the reproductive process ;—
I. ZïGNEMEÆ.
II. M e so c ak p eæ .
III. Gonatonemeæ.
íh:
We append here De Bary’s scheme of classification of this Order,
which he terms “ Conjngatæ.”
“ Cells of limited growth, propagated by unlimited repeated bipartition
(tripartite in Craierospermum) in the same direction, free or connected
ill single rows, chlorophyll in parietal bands, axile plates, or
• radiating bodies, in pairs. Cell-wall cellulose or gelatinous.
^'Fructification. By copulation a zygospore arises of a different form
from its mother-cells. No asexually produced swarmspores.
“ Subdivisions.
“ I. Mesocarpece. Zygospore the shape of the mother-cells, not contracted,
separating by three or five partitions into a central firm-walled
resting-spore and two or four lateral decaying cells. (Celia cylindrical,
united in threads, with axile plates of chlorophyll.)
“ II, Zijgyiemeoe. Zygospore undivided and mostly contracted, passing
into the resting condition, afterwards developing into a germ-cell divided
into a basal cell, and a thread-cell capable of division. (Cells cylindrical,
united in threads.)
“ III. Desmidieæ. Zygospore of the form of the Zi/gr7iemece, developing
into a germ-cell, or divided into 2 or 4, each of which separates into
two equal daughter-cells capable of division. (Cells usually consisting
of two symmetrical halves, of very various form, free or united.)”
We have adopted a similar arrangement, with the exception of the
present exclusion of the Desmidieæ, and the addition of a small subfamily,
the Gonatonemeæ, which dates from a period subsequent to
De Bary’s Memoir.
Conjugation in the present family is the union of two cells, either of
separate filaments, or of the same filament, the result being the formation
of a zygospore. The cells containing the male and female element
cannot at present be distinguished from each other, although De Bary
states that he has observed a constant difference between the fertile and
sterile cells of a species of Spirogyra. Usually all the cells of one
filament appear to be either giving or receiving cells, so th a t the male
and female filaments would seem to be distinct, but this requires more
certain confirmation, inasmuch as in such of the species of Spirogyra as
exhibit lateral as well as soalariform conjugation, all the cells in one
filament cannot be of the same kind.
“ The first perceptible change in a cell about to produce a resting-
spore appears to be a loosening of the primordial utricle from the outer
wall, and a contraction of it upon the cell-contents, which thus are
crowded together and more or less deformed. Simultaneously with
this, or a little after or before it, the side wall of the cell is ruptured, and
a little pullulation or process is pushed out, which directly coats itself
with cellulose and rapidly enlarges to a considerable diameter, at the
same time growing in length until it meets a similar process pushing out
from an opposing cell, or has attained as great a length as its laws of
development will allow. When two processes meet they become fused
together, the end walls are ruptured, and the contents of one cell passing
over are received within those of the other, or else the contents of
both cells meet within the connecting tube, and there fuse together.
This is the more common mode of conjugation, in which two cells of
distinct filaments become joined together by a connecting tube. I t is
evident that, if the filaments are fertile to their fullest extent, there
will be as many of these connecting tubes as there are pairs of cells
in the filaments, and a ladder-like body will be formed, the original
filaments corresponding to the side pieces, the connecting tubes
to the rounds. Hence this method of conjugation has received the
name of scalarifoi'm.,
“ In the so-called lateral conjugation, instead of cells of different
filaments joining, adjacent cells of one filament unite together to oom-
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