138 



SEAWEEDS 



at short intervals, so as to resemble a chain of beads, 

 though the constriction is not so deep as that would 

 imply. This basal constriction is found also in 

 Penicillus, and some species of Udotca. At the basal 

 constriction in A. comosa there are sometimes formed 



9 f 



PIG. 37. a, Arrainvillea longicaulis half natural size; b, frond filament of 

 A. Mazei ; c, ditto of A. lonoicanlis ; d, ditto, showing beginnings of branches ; 

 e, filament of A. comosa, with stoppers ; g, tip of filament of A. papuana ; f, 

 the same with dark brown contents, b, e, d, e, f, g, highly magnified. 



stoppers like those of Bryopsis and C odium. In A. 

 com.osa the filaments of the frond are free, and in 

 young specimens of A. papuana they are very little 

 interwoven. The cell-wall is uniformly thin except 

 in A. longicaulis, where it becomes (in the rhizoids) 

 so much thickened in places as to obstruct the lumen 



