216 SEAWEEDS 
GIGARTINACE. 
General Characters—The carpogonial branches 
and auxiliary cells occur in pairs, and the fertilised 
carpogonium conjugates by means of a short ooblas- 
tema filament with its auxiliary cell, which then gives 
rise to the gonimoblasts. The carpogonial branches 
and auxiliary cells rarely occur singly, but for the 
most part in groups of procarpia. The auxiliary 
cell therefore, not the fertilised carpogonium, is the 
central cell of the fruit, and the gonimoblasts, pro- 
ceeding from it, branch copiously in the surrounding 
tissue of the thallus. The order is divided into three 
families, founded on characters derived from the 
gonimoblast and the cystocarpic fruit in general. 
The first of these, Acrotylew, consisting of the two 
exotic genera, <Acrotylus and Hennedya, is dis- 
tinguished by the development of a central cavity in 
the interwoven gonimoblast and sterile thallus- 
filaments, and this cavity is then lined with the 
terminal cells of the gonimoblast which here produce 
the carpospores. Both genera are further character- 
ised by the possession of zonate tetraspores. The 
family Gigartinee, which includes the following 
British genera, Chondrus, Gigartina, Phyllophora, 
Stenogramme, Gymnogongrus, Ahnfeltia, Actinococcus, 
Callophyllis, and Callymenia, most of them common 
on our shores, does not possess the cavity which 
characterises Acrotylew, but in its place there arises 
a dense, irregular, cellular complex of gonimoblast 
and sterile tissue, in the interior of which groups of 
