raphical DiMrihution of Sea-Grasses. 1 H 1 



both tlie Iiidopatilic and the Atluiitic regions. And, as nearly all 

 are tropical, sub-tropical, or warm-temperate plants (Zosfera being 

 the only one which reaches the cold regions), the occurrence of the 

 same genus in l)oth regions indicates that the genera are so old 

 that tliey originated at a time when the distribution of sea and 

 land was very different from tliat at pi'esent — this time being at 

 least not later than Early Tertiary. 1 It is not probable that such 

 heat-requiring plants could^ have migrated from the Indopacific, 

 where they most probably originated, into the Atlantic, through 

 the cold waters either around the Cape of Good Hope or Cape 

 Horn. 



Thus their distribution seems to indicate the great age of the 

 sea-grasses, as does their low place in the natural system of the 

 Phanerogams. 



Hence it will, I think, be obvious- that a detailed study of the 

 geographical distribution, bearing in mind their systematic affini- 

 ties, may possibly throw some light on the evolution of the sea- 

 grasses, on the distribution of sea and land, and on the age of 

 the present land-bridges or land-barriers separating the oceans. 



The 8 genera of sea-grasses contain altogether only 30 species, 

 most of them having a wide distribution, as is often the case with 

 water plants. 



It will be convenient to arrange them into several groups accord- 

 ing to their geographical distribution, instead of treating each 

 species separately. 



1. — Indopacific grovp (7 species), i.e.. species which grow in 

 the Red Sea. along the coasts of East Africa and of tlie East- 

 African Isles, along the south and south-eastern coasts of Asia, in 

 the Malay Archipelago, the islands of the Pacific, and, in some 

 cases, also on the tropical coast of Australia. 



II. — Malayan group (4 species), /.^., species found in the Malayan 

 region : south-eastern coast of Asia, Malay Archipelago, and the 

 tropical coast of Australia. 



III. — East-African group (2 species), i.e.. species found only in 

 the Red Sea, along the coasts of East-Africa and of the East- 

 African isles. 



IV. — Carihhean group (6 species), i.e., species occurring along 

 the coasts of the islands of the Caribbean Sea, Florida, and the 

 north-coast of South America, some extending as far as the Ber- 

 mudas. 



idunia, perhaps even Upper Cretaceous. 



