216 SEAWEEDS 



GIGARTINACE.E. 



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, Acrotylcce, 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 Gigartinece, 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 Acrotylece, but in its place there arises 

 a dense, irregular, cellular complex of gonimoblast 

 and sterile tissue, in the interior of which groups of 



