20 



BIOLOGICAL RESULTS OF LAST CRUISE OF CARNEGIE 



slender than some (enlarged 6 diameters in figure 12). 

 The dark oogonia may readily be seen in the upper parts, 

 and even fairly evenly distributed in the receptacles, of 

 figure 11, whereas none are seen in figure 12. There is, 

 however, one oogonium in an antheridial conceptacle of 

 the receptacles represented on figure 12. In the type 

 collection of Sargassum Skottsbergii Sjost. from Easter 

 Island, described as dioecious, the author has seen an 

 occasional oogonium in an antheridial receptacle and an 

 occasional antheridial conceptacle in receptacles other- 

 wise exclusively oOgonial. 



It seems, therefore, that in this naturally smaller 

 assemblage of species passing under the names of S. 

 stenophylliun J. Ag., S. lanceolatum J. Ag., and S. Skotts- 

 bergii Sjost., the sexes may vary from partially even to 

 completely segregated, but the receptacles are more 

 properly polygamous, some plants having receptacles 

 exclusively (or almost exclusively) of one sex or the 

 other whereas other plants may have the sexes in sepa- 

 rate conceptacles but both kinds of conceptacles in the 

 same receptacle. According to the type of dominance 

 the receptacles vary, elongated and slender for recep- 



tacles purely (or approximately pure) antheridial but 

 shorter and more robust according to the admixture of, 

 or purity of, oogonial conceptacles. In plants of this 

 group from the Tonga Islands, seemingly otherwise of 

 the same species cycle, there has been seen, chiefly, 

 specimens in which oogonia and antheridia are found in 

 the same receptacle, at least in the middle parts of the 

 moderately long and moderately robust receptacles. 

 To the same smaller group as the one being dis- 

 cussed belongs also another cycle of species, viz., S. 

 Grevlllei J. Ag., S. oligocystum Mont., and S.oligocy- 

 stoides Grun. These species have broader leaves than 

 those of the Easter Island group. Their receptacles are 

 polygamous as are those of the Easter Island group, and 

 with similar variation in length-breadth index, compres- 

 sion, and absence or presence of denticulate or spinose 

 margins. Material of these species was found in some 

 collections made by the personnel of Charles Templeton 

 Crocker's Yacht Zaca, in southeastern Melanesia, dur- 

 ing June and July 1933. They are being repoi^ted on else- 

 where and tend to round out the general situation found 

 in the species of Easter and Tonga islands. 



