168 
Blackman and Tansley. 
Class III.—CONJUGATAE (AKONTAE). 
Plant-body consisting of a single cell or of an unbranched 
filament of cells. 
Chromatophores various, one or more in the cell, but always 
symmetrically arranged with reference to an axis. Pyrenoids alivays 
present. Starch always formed. Nucleus usually accurately central 
in the cell. 
Reproduction by conjugation of non-ciliate gametes (aplanogamctes), 
each derived from the whole (or nearly the whole ) body of a vegetative 
cell. Gametes never escaping from investment of cell-membrane. 
Conjugation may occur between the whole bodies cf distinct 
individuals (unicellular forms), or between the cells belonging to 
distinct individuals; or it may occur between the adjacent cells of a 
filament. The zygote in the former case may be produced isoga- 
mously in the conjugation-canal (an open tube formed between the 
two conjugating cells), or anisogamously in the cavity of the mother¬ 
cell of one of the gametes. Reproduction also by aplanospores. 
Zoospores entirely absent. All fresh-water forms. 
[The affinities of this very isolated and sharply-characterised group 
are obscure. It may possibly have been derived from a primitive motile 
green form. Chlamydomonas Braunii furnishes the closest analogy 
among the Green Algae with the peculiar method of conjugation.] 
[The classification here adopted was suggested by Palla, Bcr. d. 
dentschen But. Ges., 1894. It is largely based on the chromatophores, 
since a comparative consideration of the group shows that the nature 
of these is a more constant character than the minor differences in the 
method of conjugation usually employed to separate the families.] 
Series I. Desmidioideae. 
Plant-body unicellular , free or united in unbranched filaments ; cells 
large , of various shapes, but usually symmetrical about three planes 
at right angles to one another. Cell often constricted in one of the 
planes of symmetry (equatorial plane) often symmetrically lobed, and 
frequently with a sculptured wall. Cell-wall usually penetrated by 
protoplasmic threads, which secrete mucilage outside the wall, thus 
forming a mucilaginous sheath round the cell. 
Chromatophores usually two, one on each side of the equatorial 
plane, most frequently consisting of axile plates with symmetrically 
disposed ridges. Pyrenoids large, symmetrically arranged. Nucleus 
accurately central. 
Multiplication by bi-partition in the equatorial plane, the inner 
halves of the two daughter cell membranes being formed by the 
intercalation of new pieces between the two halves of the mother-cell, 
which form the outer halves of the two daughter-cells. 
Zygote formed in the conjugation-canal or in the cavity of one of 
the conjugating cells. 
Practically all fresh water forms, avoiding calcareous water. 
(To be continued.) 
g, MADLEY, Printer, 151, Whitfield Street, W, 
