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Such centres are especially well marked in perennial and herbaceous 
plants, somewhat also in shrubs, but in trees less so, though among them 
similar laws must be in force, when we consider the great variance in the 
prevailing types in the different localities. 
I was long inclined to ascribe these changes to the different soil, but 
afterwards I became convinced that this was not the sole cause, though it 
cannot be denied that the influence of the different geological formations on 
the limits of the centres is a very marked one everywhere. 
The whole flora of the Andamans, therefore, must be a very primary one, 
and could never have been influenced by the agency of man. Malayan prows 
come during the north-east monsoon for fishing and catching trepangs, and 
might have accidentally introduced a certain number of plants along the 
sea shores, but I saw no evidence of such a fact. 
Around Port Blair and the Penal Stations, where clearing of the jungles 
and cultivation have taken place, we may observe similar but smaller centres of 
certain introduced plants, which are now rapidly increasing and spreading 
ever the whole land so far as clearings are carried; they do not extend as 
yet into such parts of the jungles which have never been trodden 
by Europeans. It is therefore interesting to see that the extension of 
weeds and other introduced plants does not yet reach anywhere a greater 
distance from culture than a mile or so. The cause evidently is that the 
woody region does not suit them. 
Along the shores the presence of such centres is the more striking, as 
we can there easily determine their extent. As interesting examples, I 
note here Euphorbia epiphylloides , which extends on the serpentine rocks 
from the Bird-nest Gape as far as the opposite ridge at Escape Bay in Mac- 
plierson’s Straits, about two to three miles distant; it does, however, not 
go further inland than perhaps a thousand paces. This species seems to be 
peculiar to this spot, and to exist nowhere else on South Andaman. Euphorbia 
Atoto occurs in the same Bay on the sandy beach, as between South Point 
and S. Corbyn’s Cove. Its centres are, however, exceedingly small. Euphorbia, 
irigona also is restricted to the reddish serpentine, and appears on a ridge, 
extending from the southern side of the creek land inwards, thus following 
that formation. 
The most puzzling fact, however, is that commonly several species which do 
not occur elsewhere have their centres at the same place, a careful examination 
of such localities did not show me any peculiarity of configuration or soil; I 
therefore am inclined to believe that they have retreated as the sea advanced. 
It may be said that the seeds had been washed to the shores by the sea, which 
for some species really might be the case, where the nature of the seeds allow r s 
this manner of immigration. 
Although it has been proved by several eminent botanists that the germi¬ 
nating power of seeds is capable of preservation for a long period in sea-water, 
I must confess that I rarely succeeded in obtaining a single good seed amongst 
the rubbish washed out by the sea along the beaches, and those I found were 
always of such species of plants as grew along the same coasts. The great 
obstacles which meet such seeds on their new ground, which is in most cases 
only suitable for littoral plants, must also be borne in mind. Where level 
lands border the sea, these commonly are protected against any immigration 
by the dense mangrove swamps, and also where the coasts are steep; some 
sandy beach must exist to allow seeds to be washed out, or a rocky ground, 
both equally unfavorable for the greatest bulk of tropical plants. Other 
cases, I suppose, (considering only Virgin Islands,) do not occur in tropical 
Asia, as pastures, &c. There are reasons, too, to presume that rising lands, 
which owe their vegetation to the spreading of species from their interior, are 
more suited to such an immigration by sea than sinking ones. 
