Sub-Family 1. =Nemalionales.= The fertilised oosphere produces
directly the gonimoblast.
Order 1. =Lemaneaceæ.= Algæ of brownish colour and living in
fresh water. They lack tetraspores, and the very sparingly
branched fertile filaments, composed of many rows of cells, grow
out from a proembryo, which consists of a single row of cells
bearing branches. _Lemanea fluviatilis_, often found on rocks
and stones in quickly flowing streams.
Order 2. =Helminthocladiaceæ.= Tetraspores are generally wanting
(_e.g._ in _Nemalion_) or arise one in each tetrasporangium
(_e.g. Batrachospermum_) and it is only in _Liagora_
that four cruciate tetraspores are formed. _Chantransia
corymbifera_ consists of simple, branched cell-rows, and is
an independent species. Several other _Chantransia-forms_,
living in fresh water, are “proembryos” of species of the genus
_Batrachospermum_. The germinating carpospore grows out into
filaments and forms a so-called proembryo which, if not shaded,
attains only a small size, but when growing in shady situations
presents a much greater development. These highly developed
proembryos have been described as species of _Chantransia_.
The proembryo can reproduce by division, or by tetraspores
which are developed singly in the sporangia; in _B. vagum_ and
_B. sporulans_ which do not possess fully developed female
reproductive organs, the proembryos serve almost entirely to
reproduce the species. The young _Batrachospermum_-plant arises
from the end of an upright filament of the proembryo. The
proembryo is generally persistent, and continually produces new
_Batrachospermums_. These latter bear the sexual reproductive
organs and also whorls of branches: the central row of cells
is enclosed by cells growing from the base of the whorls of
branches, and from these cortical cells secondary proembryos
are developed. In this alternation of shoots there is really
no alternation of generations, since the proembryo and the
shoots with the sexual reproductive organs are parts of the same
thallus.
Several species of _Batrachospermum_ have a bluish green or
verdigris colour. _Nemalion multifidum_ has a brown-red thallus,
slightly branched, which is attached to rocks near the water’s
edge.
Order 3. =Chætangiaceæ.= _Galaxaura_ has a thallus thickly
incrusted with lime.