xxvii POTAMOGETON 369 



take the cases of Elaeocarpus, Metrosideros, and Naias. In all 

 cases we see a widely-ranging polymorphous species settling down 

 and " differentiating " in particular localities or regions, and forming 

 subcentres for the distribution of the genus. 



Potamogeton (Potameae). — Though well suited for dispersal by 

 waterfowl, the Potamogetons have been recorded from the 

 Hawaiian and Marianne Islands alone among the tropical groups 

 of the open Pacific. The genus, though not so well represented in 

 insular floras as we might have expected, is still not infrequently 

 to be found. Widely-ranging species have been observed in the 

 Azores, Madeira, and the Canaries in the Atlantic, as well as in 

 Hawaii in the Pacific ; whilst species have been recorded that are 

 peculiar to Martinique, the Mascarene Islands, and to the Marianne 

 Group. Hillebrand gives for Hawaii, Potamogeton flaitans, a plant 

 of the Old and New Worlds, and P. pauciflorus, a North American 

 species ; whilst in the Index Kewensis a peculiar species, 

 P. owaihiensis of Chamisso (which is, however, regarded by 

 Hillebrand as a form of P. fluitans), is also accredited to the 

 group. Owing, however, to the paucity of streams and rivers this 

 genus takes no prominent part in the Hawaiian flora, and the 

 species seem to have been recorded alone from Oahu. As they 

 were discovered by Chamisso in the early part of last century they 

 are in all probability truly indigenous in Hawaii, even if none are 

 peculiar to the group. 



That ducks and similar birds are the agents in carrying the 

 seeds of Potamogeton to oceanic islands cannot be doubted. 

 About twelve years ago I examined the stomachs and intestines of 

 thirteen wild ducks obtained in the London market. Three of 

 them contained in all forty-one Potamogeton seeds, or rather 

 "stones," most of which subsequently germinated in water. In one 

 of my experiments, carried out in the month of December, I fed 

 a domestic duck with the fruits of Potamogeton natans. They 

 appeared in quantity in the droppings, for the most part divested 

 of their soft coverings, but otherwise uninjured. Sixty per cent, 

 germinated in the following spring ; whilst of those left in the 

 vessel, from which the duck had been fed, only one per cent, 

 germinated in the next spring, and another year elapsed before any 

 number did so. These results were published in Science Gossip 

 for September, 1894. 



One often reads in books of travel interesting remarks bear- 

 ing indirectly on the dispersal of the Potamogetons. Thus, when 

 Sir Joseph Hooker (then Dr. Hooker) noted in his Himalayan 

 VOL. II B B 



