426 
THE SEAWEEDS 
Order GIGARTINALES Oltmanns 1904. 
Plants showing various forms from filiform to fleshy-membranous or 
crustose; corticated, with either the multiaxial or central filament types 
of structure; asexual reproduction by tetraspores formed after meiosis in 
sporangia scattered over the plant just below the surface, or in restricted 
areas on branches ; sexual reproduction by spermatangia borne on surface 
cells in more or less restricted areas and by carpogenic branches sunken in 
the cortex; typical auxiliary cells when present more or less remote from 
the carpogonia, established before fertilization, consisting of enlarged inter- 
calary cells of the cortex filaments; carpogonium after fertilization pro- 
ducing ooblast filaments which transmit the zygote nuclei to the auxiliaries, 
from which the carpospore-bearing gonimoblasts are produced. 
Family CALOSIPHONIACEAE. 
The plants belong to the central filament type, the central filament being 
particularly strong, *md supporting whorls of abundantly branched short 
filaments similar to Batrackospermum. The carpogonia are three celled 
and arise from the lower cells of the assimilatory short filaments. The 
supporting cell unites with the fertilized carpogonium and forms the com- 
pound filaments. The auxiliary cell unites with one of the basal cells of 
the assimilatory short-filament system, and then divides more or less out- 
wards to form a first gonimoblast cell. These usually form opposite the 
region where the compound filaments fuse with the auxiliary cell. From 
the first gonimoblast cell develop more densely crowded gonimoblast fila- 
ments, then all cells produce carpospores. The gonimoblasts lie among the 
short filaments; protecting filaments are not formed. 
Family NEMASTOMACEAE. 
Foliaceous or branching plants, rather soft with longitudinally fila- 
mentous medulla and compact radially filamentous cortex ; sporangia tetra- 
partite or lacking; spermatangia developed on the outermost cells of the 
cortex; carpogenic branches of three to seven cells developed on the cor- 
tical filaments; auxiliary cells scattered, intercalary, developed in inner 
segments of corticating filaments, ooblast filaments from the carpogonidia 
penetrating through the interfilamentous spaces to reach the auxiliary cells ; 
cystocarps developed outwardly from the auxiliaries, the gonimoblasts com- 
pletely maturing into carposporangia and without special pericarp struc- 
tures surrounding them. 
Nemastoma J. Ag. 
Family SEBDEN1ACEAE. 
The thallus is of the 4 ‘ fountain ' ’ type. The cortex consists of thickly 
packed filaments giving a parenchymatous appearance, while the medullary 
tissue shows a looser filamentous structure. The Sekdeniaceae represent a 
