126 A NATURALIST IN THE PACIFIC chap. 



with the other indigenous species of Citrus, the fruits floated lightly 

 and protruded half-way out of the water. 



There is nothing trivial in these examples of buoyant fruits. 

 That they have at times aided in the dispersal of the genus, with 

 man's assistance in planting the seeds of the stranded fruits, I 

 cannot doubt ; but unaided by man such buoyant capacities would 

 be useless for purposes of effective dispersal by currents. Between 

 the two genera Terminalia and Citrus there is this great distinction, 

 that the former is more or less halophilous, some of its species 

 being at home on the sea-beaches, whilst the latter, as Schimper 

 would term it, is salt-shy, and includes no halophytes or plants of 

 the sea-shore amongst its species. The only effect of buoyancy of 

 the fruits on the distribution of the species of Citrus would be to 

 place them by the side of the river and the pond. This has 

 evidently been its result in the case of the Shaddock in Fiji, where, 

 as Seemann remarks, it often thickly lines the banks of the rivers. 

 As also indicating that the buoyancy of the seed or fruit would 

 never, apart from the halophilous habit, endow an inland plant 

 with a littoral station, the examples of the Oak (Quercus robur) 

 and of the Hazel (Corylus avellana) may be taken. As shown in 

 Note 48, these fruits acquire floating power by drying, on account 

 of the space formed by the shrinking of the kernel. They occur 

 commonly in beach drift, but rarely in a sound condition ; yet 

 experiment has proved that they will sometimes germinate after 

 prolonged sea-water flotation. The fruits of other species of 

 Quercus are also transported in tropical regions by the currents, 

 but never, as far as I could learn, effectively. The Amentaceae as 

 an order are " salt-shy," and with only a few exceptions shun the 

 sea-beach. 



In the great sorting-process, by which xerophytic plants with 

 buoyant seeds or fruits have been placed at the coast, and hygro- 

 phytic plants with similar fruits or seeds have been stationed at 

 the riverside or by ponds and lakes, one might expect to find 

 that other influences may have at times been in conflict with the 

 selecting operation here indicated. To this cause may probably 

 be attributed the cases of " useless buoyancy " above referred to. 

 Here we find in some inland plants fruits and seeds with buoyant 

 tissues in their coverings that in the case of littoral plants would 

 have been regarded as the result of adaptation to dispersal by 

 currents. Such cases go to emphasize the conclusion already 

 indicated that these tissues could not have been developed through 

 the agency of Natural Selection. But the great objection against 



