16 THE GEOGRAPHY OF PLANTS. 



a few hundred feet. The depth of the ocean 

 varies very greatly, and animals and plants are 

 alike absent from its deeper parts. The plants 

 included under the name of marine plants are 

 the immense family of Algce, or sea- weeds, and 

 the single genus of flowering plants, termed 

 zostera, or grass wrack, of which we have two 

 native species existing in our British seas, one 

 of which is extremely abundant. Most of the 

 marine plants are rooted on the bottom of the 

 sea, or on rocks, or even on other sea-weeds, 

 chiefly in shallow water, and must, therefore, 

 derive all their nourishment from the sea- water 

 and the air it contains. There are exceptions 

 to this, such as in the sea-weed now called Sar- 

 gassum vulgare. This very remarkable plant 

 forms beds of vast extent over a space in the 

 Atlantic Ocean, which is called the Sargasso 

 Sea, (Mar de Zargasso of the Portuguese,) and 

 which extends from 22 to 36 N. lat, and 

 from 25 to 45 w. long., an area equal to 

 40,000 square miles, or the whole of France. 

 So vast are some, of these beds of sea- weed, that 

 Columbus, who met with them in his first 

 voyage westward, in which he discovered the 

 western hemisphere, compared them to floating 

 meadows. Their occurrence induced him to 

 expect the vicinity of land long before the 

 realization of his hopes and predictions, and 

 enabled him for some time to repress the mu- 

 tinous disposition of his wearied and dispirited 

 seamen. It is singular that this sea-weed has 

 never been ^ound with either root or fruit, and 



