OF THE MALDIVE ISLANDS. 
159 
owe their position to the lakes having been at some time in 
direct. communication with the sea. This is probable also 
on geological grounds, while the lake at Huludu, Addu Atoll, 
which has no mangrove, was apparently due to other causes. 
VIIL^TRE FLORAS OF OCEANIC ISLANDS. 
There now remain to be discussed, very briefly, some 
features of the more general bearing of the above facts on 
questions of geographical distribution in general. Firstly, 
as to the much discussed question of the origin of the floras 
of oceanic islands. It is evident that in a tropical island, 
man’s interference being supposed absent, we shall get, on 
the beach, and in the case of an island with a loftier centre 
also to some extent inland, the littoral sea-borne species of 
the ocean in which the island lies. If not too far removed 
from the mainland, bird-introduced littoral species will also 
appear, and also probably some other inland species which 
will become established if the island be big enough and 
raised enough to permit them to grow independently of the 
littorals. Wind will bring species of fern^ and other cryp- 
togams, and possibly a few Compositæ or other flowering 
plants. Now, suppose the island to have been in the first 
place quite free of any vegetation, and consider what may 
happen in the course of a long period of time. The further 
history of the littorals and of the inland species will almost 
certainly be quite different. The former will come in large 
numbers, depending on the currents passing the island, but 
the available area for their growth will be small, and the 
competition greater. Continual crossing with new arrivals 
will probably help to keep the type constant, and we shall 
not expect to find many endemic forms developing from the 
littoral flora. If any such should form and remain littoral 
in their habitat, they will probably spread about the ocean 
like the other species that first came to the island, and their 
place of origin may be finally undiscoverable. With the 
inland forms introduced by wind and birds the case will be 
