146 THE PLANTS 



broad basal leaves, and long branching shoots of a secon- 

 dary order, with, as a rule, leaves of different size, air 

 vesicles, and special fruiting branches. When basal 

 and upper leaves differ from each other the transition 

 is gradual. The fruiting branches bear conceptacula 

 which are highly differentiated in the different species. 

 In some species the branches with male conceptacula 

 seem to be cylindrical, and those with female concep- 

 tacula dentate, but this question must still be carefully 

 investigated. It is important, because J. G. Agardh 

 divided the Sargassa into various groups, according to 

 the form of the conceptacula-bearing branches. 



The genus Sargassum has approximately 150 species, 

 and is distributed over the warmer temperate and 

 tropical seas ; it is especially frequent on the coast of 

 Australia. One species has for four centuries attracted 

 the attention of men of science Sargassum bacciferum, 

 the alga of the famous Sargasso Sea. Discovered by 

 Columbus, described by Humboldt, the origin of these 

 enormous quantities of drifting seaweed is, after four 

 centuries, still practically unknown. There are two 

 opinions about the origin of Sargassum bacciferum. 

 Humboldt, Forbes, Piccone, A. Agassiz, allow the possi- 

 bility of the present Sargassum bacciferum being the 

 floating form of one or more Sargassa that lived at- 

 tached in a former period of the earth. If this were 

 true, S. bacciferum should have propagated itself 

 vegetatively for long ages, because it has been col- 

 lected almost always in a barren state. Krummel is 

 of another opinion. In his beautiful work, " Die 

 Reisebeschreibung der Plankton - Expedition," he 

 gives a very interesting chart of the distribution of 

 S. bacciferum in the Atlantic, thereby dispelling the 

 error of Humboldt, who believed in the existence of 

 two fixed banks of Sargassum. Krummel assures us 



