306 DISTRIBUTION OF MARINE' PLANTS. [SKCT. xxvu. 



such quantities, that the early Portuguese navigators, Co- 

 lumbus and Lerius, compared the sea to extensively inundated 

 meadows, in which it actually impeded their ships and 

 alarmed their sailors. M. de Humboldt, in his Personal 

 Narrative, mentions that the most extensive bank of sea- 

 weed is in the northern Atlantic, a little west of the meridian 

 of Fayal, one of the Azores, between the 25th and 36th 

 degrees of latitude. Vessels returning to Europe from 

 Monte Video, or from the Cape of Good Hope, cross this 

 bank nearly at an equal distance from the Antilles and 

 Canary Islands. The other bank occupies a smaller space, 

 between the 22nd and 26th degrees of north latitude, about 

 eighty leagues west of the meridian of the Bahama Islands, 

 and is generally traversed by vessels on their passage from 

 the Caicos to the Bermuda Islands. These masses consist 

 chiefly of one or two species of Sargassum, the most extensive 

 genus of the order Fucoidese. 



Some of the sea-weeds grow to the enormous length of 

 several hundred feet, and all are highly coloured, though 

 many of them must grow in the deep caverns of the ocean, 

 in total or almost total darkness ; light, however, may not 

 be the only principle on which the colour of vegetables 

 depends, since M. de Humboldt met with green plants grow- 

 ing in complete darkness at the bottom of one of the mines at 

 Freyberg. 



It appears that in the dark and tranquil caves of the ocean, 

 on the shores alternately covered and deserted by the restless 

 waves, on the lofty mountain and extended plain, in the 

 chilly regions of the north and in the genial warmth of the 

 south, specific diversity is a general law of the vegetable 

 kingdom, which cannot be accounted for by diversity of 

 climate; and yet the similarity, though not identity, of 

 species is such, under the same isothermal lines, that, if the 

 number of species belonging to one of the great families of 

 plants be known in any part of the globe, the whole number 

 of the phanerogamous or more perfect plants, and also the 



