374 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



whorl, branches patent, more or less incurved, membrane firm, 

 color dull green, forming dense tufts, many cm. diam. Ber- 

 muda. Indian and Pacific Oceans. 



Like V. vcrticillata this species has whorled branches, but the 

 whorls are fewer branched and less frequent ; the cells are 

 many times longer. 



3. SIPHONOCLADUS Schmitz, 1878, p. 17. 

 Frond originating in a simple clavate cell, attached by multi- 

 cellular rhizoids at the base, of definite growth ; ultimately be- 

 coming multicellular by the transformation of the contents into 

 cyst-like cells, uniting sub-parenchymatously, then each push- 

 ing through the mother cell wall, assuming a shape like the 

 mother cell and developing in the same way as the latter. 

 Asexual reproduction by escape and growth of the cysts ; re- 

 production also by zoospores formed in large numbers in the 

 clavate cells; probably asexual. Ordinary cell division by 

 cross walls not certainly observed. 



The primary cell in Valonia appears to bear branches with a 

 partition at the base of each ; in Siphonocladus a multicellular 

 filament appears to take the place of the primary cell, each cell 

 of the filament producing a branch without partition at the base. 



KEY TO THE SPECIES OF SIPHONOCLADUS. 



i. Primary cell long, erect ; substance soft. i. S. tropicus. 



i. Primary cell short ; substance firm and crisp. 2. .5". rigidus. 



1. S. TROPICUS (Crouan) J. G. Agardh, 1886, p. 105; 

 Howe, 1905, p. 245, PI. XIII, fig. 2 ; Vickers, 1908, p. 20, PI. 

 XVIII. Primary cell up to 4 cm. long, i cm. wide, with 

 annular constrictions near the base ; branches similar, also with 

 constrictions near base, often longer than the primary cell ; 

 cells of third generation similar but generally shorter ; zoospores 

 many in a cell which has reached its full growth, escaping by 

 small perforations in the walls. Fla., W. I. 



2. S. RIGIDUS Howe, 1905, p. 244, PI. XII, fig. i ; PI. XIV ; 

 P. B.-A., No. 1489; 5. tropitus P. B.-A., No. 1031. Frond a 

 more or less dense tuft of pale green, crisp filaments, main axis 

 hardly distinguishable ; branching sub-dichotomous, irregular, 

 or secund ; filaments 350-1100 ^ diam., often united by short 

 tenacula. Fig. 139. Bahama. 



Howe's description of this species was apparently written 

 without knowledge of Borgesen, 1905, which was published 

 about the same time ; in the light of Borgesen's studies of .5". 



