Order 12. =Rhodomelaceæ.= _Rhodomela_, _Odonthalia_;
_Polysiphonia_, of which many species are to be found on the
coasts of Great Britain, has a filamentous, richly branched
thallus consisting of a central row of cells surrounded by a
varying number of cortical cells of similar size--the so-called
“siphons.”
Order 13. =Ceramiaceæ.= Pretty Algæ, often branched
dichotomously, or unilaterally pinnate. _Spermothamnion,
Griffithsia, Callithamnion, Ceramium, Ptilota._
Sub-Family 4. =Cryptonemiales.= The cells formed by the
coalescence of the auxiliary cells and the ooblastema-filaments,
produce the gonimoblasts. The _carpogonium-filaments_ and
the auxiliary cells are scattered singly in the thallus.