The gonimoblasts may arise in three ways:—
1. In the Nemalionales, branched filaments grow out from the oosphere and form an upright, compressed or expanded tuft of spore-forming filaments.
2. In the Cryptonemiales, several branched or unbranched filaments (ooblastema-filaments) grow out from the oosphere, and conjugate in various ways with the auxiliary cells. The gonimoblasts are then formed from the single cells produced by the conjugation.
3. In the Gigartinales and Rhodymeniales the oosphere conjugates with an auxiliary cell by means of a short ooblastema-filament, and from this auxiliary cell a gonimoblast is produced.
The motionless carpospores, which sometimes in the early stages are naked, and afterwards invested with a cell-wall, are developed from the terminal cells (and perhaps also from some of the other cells) of the branches of the gonimoblast. The gonimoblasts constitute sharply defined parts of the plant in which the carpospores arise. These parts are called cystocarps and are either naked (Fig. [77] E), or surrounded by a covering (pericarp or involucre, Fig. [77] A) formed in different ways. On this account the Florideæ were formerly divided into Gymnosporeæ (Batrachospermum, Nemalion, Ceramium, etc.) and Angiosporeæ (Farcellaria, Lejolisia, Delesseria, Melobesia, etc.).
The Florideæ are divided into four sub-families:—
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.