MARINE ALG^E OF BEAUFORT, N. C. 451 



Genus 2. Sargassum Agardh. 

 Sargassum, Agardh, 1820, p. i. 



Frond attached by a basal disk or free floating, consisting of evident stem and leaf 

 like portions, bearing, in addition to these, vesicles and receptacles as separate organs; 

 main axis short; branching lateral, alternate, decompound; stem terete, flattened, or 

 angular; leaves variously shaped, sometimes branched, consisting of a flattened lamina 

 usually on a short petiole, provided with a more or less conspicuous midrib traversing 

 the entire leaf or extending through only the lower half, lamina sometimes reduced so 

 that the leaf consists of little more than the midrib, margins smooth, serrate, or dentate; 

 vesicles spherical, ellipsoidal, or obovate, sometimes flattened, occurring singly, formed 

 from transformed leaves or parts of leaves (the transformation taking place at a young 

 stage), borne on short stalks, often with flat, unaltered portions of the leaf remaining 

 along the stalk and at the apex of the vesicle, the remnant at the apex often reduced to 

 a spinelike tip; cryptostomata present only on the leaves, sometimes lacking; recep- 

 tacles simple or branched, terete, flattened, or angular, often axillary; conceptacles 

 usually spherical, communicating with the exterior by a narrow canal, hermaphroditic; 

 oogonia accompanied by a few simple or branched paraph yses, producing only one egg ; 

 antheridia rotund on racemosely branched filaments. 



About 1 60 species, grouped in five subgenera containing numerous sections, in warm 

 and temperate seas throughout the world, especially in Australian region. 



Some of the species are easily distinguishable, but most of them are separated by 

 slight, inconspicuous characters. With the large number of species separated by slight 

 differences, it is difficult to give an idea of these differences by descriptions. Determi- 

 nations here, more than in most genera, can be made only by comparison with authentic 

 specimens. 



Seventeen species are reported for North America", 15 being found on the eastern 

 coast. Most of these are southern, only one, S. filipendula, extending to the north, with 

 one other, 5. natans, often washed ashore. In the region studied, attached forms are 

 apt to be 5. filipendula, and floating ones are apt to be 5. filipendula var. montagnei 

 if fertile, or S. natans if sterile, although an occasional representative of other species may 

 be found washed ashore. 



While the extreme forms of these two species are easily distinguished, intermediate 

 forms approach each other. Some specimens referred to S. natans by various workers 

 bear a closer resemblance to S. fiUpendida var. montagnei. Such specimens will give 

 much trouble to those who may try to name them. 



Observations of Tahara and others show that in some species of this genus eggs are 

 produced periodically at intervals of five to eleven days, apparently bearing no definite 

 relation to the tides. 



KEY TO SPECIES. 



Cryptostomata usually lacking, leaf margins conspicuously serrate, branching rather irregu- 

 lar, usually sterile i- 5. natans (p. 452). 



Cryptostomata present, usually conspicuous, leaf margins often not conspicuously serrate, 



branching fairly regular, usually fruiting 2. 5. filipendula (p. 452). 



