4o8 A NATURALIST IN THE PACIFIC chap. 



over a wide extent of ocean were small. None of them survived 

 twenty-four hours' drying in fine weather, whether in the sun or in 

 the shade ; but in rainy weather they withstand an exposure of one 

 or two days. It is, therefore, unlikely, even if the fronds were 

 entangled by their rootlets in a bird's feathers, that they would be 

 able under ordinary conditions to reproduce the plants after a day's 

 flight of some five hundred miles across the sea. It must also be 

 remembered that the drying capacity of the air when a bird is in 

 full flight in ordinary weather would be that displayed during a 

 gale of wind with a velocity of at least thirty to forty miles an 

 hour. For this reason I do not think with Kerner that under usual 

 conditions drops of water would be a factor of importance in 

 causing the adherence of minute seeds of any kind to birds' plum- 

 age. Where the seeds are not available, it is most probable that 

 birds disperse the duckweeds by their fronds over short distances, 

 but not across broad seas. This would certainly apply to temper- 

 ate latitudes, where these plants rarely seed. Thus with Lemna, 

 as with Ceratophyllum, it would seem that the dispersal of the 

 seeds by birds takes place normally only in warm latitudes. 

 Those of the duckweeds could be transported in adherent mud 

 over land-areas. 



According to Hegelmaier, the two species of Lemna found in 

 Fiji are L. paucicostata, an Asiatic species, and a variety of an 

 Australian species, L. oligorrhiza, possessing dark root-sheaths. 

 These plants mostly came under my notice in the Rewa delta. 

 They were rarely seen in Vanua Levu, where in one locality I found 

 the typical Lemna minor. The first species is also Samoan. 



In 1897 and in 1899, in a pool near Notho in the Rewa delta, 

 in Viti Levu, Fiji, I found a great abundance of a species of 

 Wolffia, specimens of which were sent to Prof. Schimper with my 

 mangrove collections, but his death intervened, and I have not been 

 able to follow up the matter. On comparing the specimens with 

 Hegelmaier's descriptions and plates, it would seem that the 

 species is near W. arrhiza and W. brasiliensis, but differs from both 

 in the greater length of the fronds. As concerning the means of 

 dispersal of the genus, I may add that the fronds were killed after 

 being allowed to dry for eighteen hours. 



Marsilea (Marsileacese) 



A species of this genus, apparently near Marsilea villosa, was 

 common in the ditches and ponds around Notho, in the Rewa 



