78 A NATURALIST IN THE PACIFIC chap. 



the species have a much wider distribution. Avicennia officinalis has 

 a cosmopolitan distribution in the tropics and beyond, occurring as 

 it does on the Atlantic and Pacific coasts of America, on both 

 coasts of Africa, over Asia and Australia, as well as in New 

 Caledonia and New Zealand, but not in Polynesia {Bot. Chall. 



Exped., III., 178) I have now gone far enough to show that 



the tendency displayed by the seeds and fruits of several of the 

 plants of the mangrove-formation to germinate either on the tree 

 or in the floating drift of estuaries has not affected the general 

 distribution of the species in its main outlines. Few fruits are 

 found more often in a germinating condition in the floating drift 

 of the Rewa River in Fiji than those of Barringtonia racemosa, 

 yet the species ranges from the African East Coast eastward to 

 Polynesia. Seedlings as well as seeds or fruits, whether or not in 

 a germinating condition, are, therefore, able in such cases to disperse 

 the species. 



This readiness of the floating fruits of plants of the mangrove 

 formation (excluding the viviparous species) to germinate in the 

 estuaries is, I am inclined to think, due in the main to the strain of 

 vivipary that runs through nearly all the plants of the mangrove- 

 swamp and of its borders. It would, indeed, appear that the 

 viviparous habit (the capacity of germinating on the plant) which 

 finds its extreme development in Rhizophora and Bruguiera of the 

 Fijian swamps is represented in its earliest stage in the readiness 

 of the floating fruits of Barringtonia racemosa, Carapa obovata, &c., 

 to germinate in the Fijian estuaries, and as remarked in Note 37 

 there is a suspicion of vivipary in the instances of both the species 

 just named. Intermediate cases, as that of Laguncularia in the 

 Ecuador swamps, occur in other regions with species where 

 germination only takes place at times on the plant. This subject 

 is, however, generally discussed in Chapter XXX. and need not 

 be further dealt with here. 



A predisposing cause of the germination of floating seeds and 

 fruits in tropical estuaries would seem to be afforded by the super- 

 heating of the water of the estuary. This came under my notice 

 both in the Rewa River in Fiji and in the Guayaquil River in 

 Ecuador, where the water of the estuary is often noticed to be 

 some degrees warmer than that of the sea outside, and of the 

 water from the river above the estuary. (See Note 38.) 



We come now to the subject of the non-germination in tropical 

 estuaries of the floating fruits of the beach-trees, such as Bar- 

 ringtonia speciosa and Cerbera OdoUam, that in the Pacific islands 



