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 Udotea. At the basal 
constriction in A. comosa there are sometimes formed 
Fic. 87.—a, Arrainvillea longicaulis half natural size; b, frond filament of 
A. Mazei; c, ditto of A. longicanlis ; d, ditto, showing beginnings of branches ; 
e, filament of A. comosa, with stoppers ; o tip of fil: iment of A. papuana; fy 
the same with dark brown contents. 0b, c, d, e, f, g, highly magnified. 
stoppers like those of Bryopsis and Codium. In A. 
comosa 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 
