268 DISTRIBUTION OF MARINE PLANTS. SECT. XXVII. 



bus and Lerius, compared the sea to extensively inun- 

 dated 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, be- 

 tween 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 22d 

 and 26th degrees of north latitude, about eighty leagues 

 west of the meridian of the Bahama Islands, and is gen- 

 erally 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 ex- 

 tensive genus of the order Fucoideae. 



Some of the sea- weeds grow to the enormous length 

 of several hundred feet, and all are highly colored, 

 though many of them must grow in the deep caverns of 

 the ocean, in total or almost total darkness ; light how- 

 ever may not be the only principle on which the color of 

 vegetables depends, since M. de Humboldt met with 

 green plants growing 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 vegqjplble kingdom, which cannot be accounted for 

 by diversity of climate : and yet the similarity, though 

 not identity, of species is such, under the same isother- 

 mal 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 number of species com- 

 posing the other vegetable families, may be estimated 

 with considerable accuracy. 



Various opinions have been formed on the original or 

 primitive distribution of plants over the surface of the 

 globe ; but since botanical geography became a regular 



