XXVII MARSILEA 



409 



delta, Fiji, in 1897-99. The genus is included by Home in his list 

 of Fijian plants ; but is not given by Seemann. The villous 

 sporocarps, when dry, are very light and readily catch in cloth and 

 in feathers. Hillebrand includes in the Hawaiian flora M. villosa 

 and M. crenulata. The first-named, which was collected by 

 Chamisso and Gaudichaud, finds (he says on the authority of 

 Braun) its nearest relative in a species from 0'"egon and California. 

 The other has been collected in the Liukiu Islands, the Philippines, 

 Mauritius, and Bourbon. It is very probable that the occurrence 

 of the genus in oceanic islands is due to the agency of birds. 



Summary of the Chapter 



(i) We are here concerned with the more restricted distribution 

 of non-endemic tropical genera over the Pacific. The general trend 

 eastward of these genera is well brought out in the fact that whilst 

 Fiji possesses some sixty or seventy genera in common with 

 Tahiti to the exclusion of Hawaii, it does not possess a score 

 in common with Hawaii to the exclusion of Tahiti. The grasses 

 and sedges and the mountain genera are not here included ; and 

 we are comparing the flora of the Hawaiian lowlands below 4,000 

 feet with the floras in mass of Fiji and Tahiti. 



(2) Hawaii possesses very few genera (less than thirty) that are 

 not found either in Fiji or in Tahiti, or in both ; and of these quite 

 a third are to be traced to America. 



(3) From two of these genera, Embelia, a land genus, and 

 Naias, an aquatic genus, we obtain two important indications, 

 namely, that specific differentiation has taken place to much 

 the same extent in a water plant as in a land plant, whether 

 in a continent or in an island. In other words, new species have 

 been developed or are developing independently of the immediate 

 environment and of isolating influences. 



(4) The interchange of plants between the regions of Hawaii 

 and Tahiti to the exclusion of Fiji has been very slight. Probably 

 not half a dozen genera belong to this category. 



(5) Excluding plants brought by man and by the currents, 

 Tahiti possesses very few that present any difficulty from the 

 standpoint of dispersal, plants with seeds or "stones " an inch in 

 size being, as a rule, absent. 



(6) With the genera (60 — 70) common to Fiji and Tahiti, and 

 distributed, therefore, over the South Pacific, the wide-ranging 



