SECT. XXVII. DISTRIBUTION OF MARINE PLANTS. 267 



Tt appears from the investigations of M. de Humboldt, 

 that between the tropics the monocotyledonous plants, 

 such as grasses and palms which have only one seed- 

 lobe, are to the dicotyledonous tribe, which have two 

 seed-lobes like most of the European species, in the 

 proportion of one to four ; in the temperate zones they 

 are as one to six; and in the Arctic regions, where 

 mosses and lichens which form the lowest order of the 

 vegetable creation abound, the proportion is as one to 

 two. The annual monocotyledooous and dicotyledonous 

 plants in the temperate zones amount to one-sixth of 

 the whole, omitting the Cryptogamia (N. 214) ; in the 

 torrid zone they scarcely form one-twentieth, and in 

 Lapland one-thirtieth part. In approaching the equa- 

 tor, the ligneous exceed the number of herbaceous 

 plants, in America there are a hundred and twenty 

 different species of forest trees, whereas in the same 

 latitudes in Europe only thirty-four are to be found. 



Similar laws appear to regulate the distribution of 

 marine plants. M. Lamouroux has discovered that the 

 groups of algae, or marine plants, affect particular tem- 

 peratures or zones of latitude, though some few genera 

 prevail throughout the ocean. The polar Atlantic basin, 

 to the 40th degree of north latitude, presents a well-de- 

 fined vegetation. The West Indian seas, including the 

 Gulf of Mexico, the eastern coast of South America, the 

 Indian Ocean and its gulfs, the shores of New Holland, 

 and the neighboring islands, have each their distinct 

 species. The Mediterranean possesses a vegetation 

 peculiar to itself, extending to the Black Sea ; and the 

 species of marine plants on the coast of Sj^ia and in 

 the port of Alexandria differ almost entirely from those 

 of Suez and the Red Sea, notwithstanding the proxim- 

 ity of their geographical situation. It is observed that 

 shallow seas have a different set of plants from such as 

 are deeper and colder; and, like terrestrial vegetation, 

 the algae are most numerous toward the equator, where 

 the quantity must be prodigious, if we may judge from 

 the gulf-weed, which certainly has its origin in the 

 tropical seas, and is drifted, though not by the gulf- 

 stream, to higher latitudes, where it accumulates in such 

 quantities, that the early Portuguese navigators, Colum- 



