MARINE ALGAE 



19 



ical waters. This is indicated by the attribution of 

 Macrocystis and Lessonla, and even of Durvlllaea, spe- 

 cies of the west South American coasts to such tropical 

 localities as the coasts of Tahiti. 



Nevertheless, patches of floating seaweeds may be 

 seen at times near the various islands or archipelagoes 

 within the tropics (or warmer waters) and forms ap- 

 proaching very closely to S. natans (L.) Meyen (S. bac- 

 ciferum [Turn.] C. Ag.) are to be found in herbaria, des- 

 ignated as from Indo-Pacific areas. The exact locali- 

 ties are not always certain, but it may be presumed that 

 at times the Atlantic species may pass around the Cape 

 of Good Hope. Indigenous Indo-Pacific species of Sar- 

 gassam may be suspected as possible of adopting, as 

 well as adapting themselves to, a pleuston (or continued 

 floating and self -propagating existence), but there is lit- 

 tle certainty in this direction. Sample 318, taken in con- 

 nection with samples 309 and 317, is a plausible sugges- 

 tion along this line and may have a bearing on the ques- 

 tion as to a limited type of Sargasso Sea in the south- 

 eastern tropical Pacific. 



The Sargass«un of samples 309, 317, and 318 raise 

 morphological, taxonomic, and distributional questions. 

 Sample 309 is composed of attached specimens, living at 

 a depth of 15.4 fathoms. As already stated, this species 

 agrees most nearly with the description of Sargassum 

 lanceolatum J. ^g. J. G. Agardh, however, does not indi- 

 cate of what sex (or sexes?) his type specimens were, 

 but Grunow states that the receptacles in this species 

 (as he understands it) are androgynous. It seems that 

 some dioecious species may have androgynous states 

 (or possibly seasonal conditions). It has not been possi- 

 ble to examine the type plants (from the west coast of 

 Australia, preserved in Herb. Mus. Paris), so the deter- 

 mination as to S. lanceolatum is not fully substantiated. 



The only species hitherto known with certainty from 

 Easter Island is Sargassum Skottsbergii Sjostedt (in 

 Skottsberg, The Natural History of Juan Fernandez and 

 Easter Island, vol. II, part III, p. 311, 1924). The plants 

 of this species are very close to those of sample 309, 

 except that the leaves of the antheridial plant are entire 

 or only sparingly and minutely denticulate, with few (at 

 times no) and inconspicuous cryptostomata, whereas 

 those of the oOgonial plant are more conspicuously and 

 acutely denticulate, with the cryptostomata more numer- 

 ous and conspicuous. The receptacles vary somewhat in 

 both Sjostedt's plants, and the Carnegie samples 317 and 

 318 are fully as much swollen as those figured by SjO- 

 stedt (loc. cit., fig. 3), and thoroughly merit his descrip- 

 tion of "breviora, latiora, conica." Plants appearing to 

 be identical with those of S. Skottsbergii occur common- 

 ly on the shores of Tongatabu in the Tonga Archipelago. 

 Both, however, seem to correspond in detail to the de- 

 scription of S. stenophyllum J. Ag., from the western 

 shores of Australia (type specimen in Herb. Mus. Paris, 

 not seen). Grunow says that the receptacles of the type 

 specimen of S. stenophyUum are androgynous, whereas 

 all the Tongatabu and Easter Island specimens examined 

 seem varyingly androgynous or polygamous (i.e. recep- 

 tacles with exclusively male and female conceptacles, 

 receptacles with^largely male or female conceptacles, 

 and finally receptacles with conceptacles in which male 

 and female are mixed). Therefore the three species 

 represented by the binomials S. stenophyllum J. Ag., S. 

 lanceolatum J. Ag., and S. Skottsbergii Sjost., seem very 

 near to one another, sufficiently so to form a narrow spe- 

 cies group, or even possibly a species cycle. Assuming 



that S. stenophyllum J. Ag. (1848) may be the same as S. 

 Skottsbergii SjOstedt, the latter name has the preference 

 since S. stenophyllum Martins (now S. cymosum C. Ag.) 

 dates from much earlier (at least as early as 1827) than 

 S. stenophyllum J. Ag. (1848). If all are considered to be 

 only members of one form cycle about S. lanceolatum 

 J. Ag. (1848), this name will apply, the S. lanceolatum 

 Greville (1849) being different (now S. coriiiollum J. Ag.) 

 from S. lanceolatum J. Ag. (1848), and of sufficiently 

 probable later date of publication as to be rejected (not 

 being an earlier homonym). 



A number of photographs are reproduced in connec- 

 tion with the collection of samples 309, 317, and 318, in 

 order to make more clear and more certain than may be 

 accomplished by words, the variation of the receptacles 

 in size, shape, and the coordination with sex segregation. 



Figure 1 shows two plants of diverse age and devel- 

 opment of sample 309, from fourteen fathoms depth off 

 Easter Island. The younger plant (above) shows the 

 short main axis (characteristic of this species group) 

 giving off several lateral axes. The older plant is only 

 the upper part of a lateral axis, with branches, leaves, 

 and well-developed receptacles which are antheridial. 

 Figure 2 shows the receptacular branchlet enlarged 6 

 diameters. The coarse, compact, cymose receptacle is 

 somewhat flattened and sufficiently condensed to be den- 

 tate on the margins (because of suppressed branchlets). 

 Because of this, the Agardhian arrangement would re- 

 move this plant far from those of the other numbers (in- 

 to the "Series" Acanthicarpicae, "Tribe" Biserrulae 

 of J. G. Agardh). This seems unsuitable from other re- 

 semblances of habit and structure between this and the 

 other numbers of the Carnegie collections and also from 

 plants collected in the Tonga Islands. 



Figure 3 shows a sheet of fragments of collection 

 sample 317, collected floating about two miles northeast 

 of Easter Island, but it seemed to be fairly recently torn 

 away. The two lower fragments have elongated, slender 

 antheridial receptacles (see figure 4,o*), whereas those 

 of the upper row have shorter, more robust receptacles 

 (see figure 4,?), antheridial below, oogonial toward the 

 apex. Figure 5 shows receptacles from the fragments 

 shown 6 diameters. The details of the long, slender an- 

 theridial receptacles and the short, robust receptacles 

 with antheridial conceptacles below and oogonial recep- 

 tacles above are shown. The receptacles of sample 317 

 are from fragments, are neither definitely flattened nor 

 toothed, and consequently are not ancipate. They differ 

 in these respects from those of sample 309. Sample 309 

 would be placed under "Series" Malacocarpicae, "Tribe" 

 Cymosae of J. G. Agardh. 



Figure 6 shows receptacular branchlets from two 

 fragments of still other plants of sample 317, both oOgo- 

 nial toward the apex, but antheridial below. The dispro- 

 portion between the length -breadth indices of the two sets 

 of receptacles is marked. 



Figure 7 shows four samples from the mass of float- 

 ing fragments of the light yellowish color characteristic 

 of the floating fragments from the Atlantic Sargasso Sea, 

 under sample 318. The mass of sample 318 was floating 

 about eight miles southeast of Easter Island. 



Figure 8 shows characteristic sterile fragments 

 from this collection, whereas figures 9 and 10, enlarged 

 2 diameters, show characteristic fruiting fragments, Iwth 

 with androgynous receptacles. In figure 9 these are 

 shorter and more robust (as seen enlarged 6 diameters 

 in figure 11). In figure 10 they are longer and more 



