256 
since but for the existence of the Settlement the ditches and pools in 
which they occur would not exist. The agency of winds, so often 
supposed to be highly effective, suggests itself for very few of the 
species, the most probable being the Selaginella and the Gheilantlies ,— 
almost the only posssible one among phanerogams being the Galotropis. 
But if these be wind-introduced species then as regards all three 
the questions at once arise ;—why were they not to be found in 1866 ? 
and, why are they only to be found within the limits of the Settlement 
now ? And as regards Selaginella a closer enquiry makes the agency 
of wind highly improbable, for it is as yet only to be found on Ross 
Island, although there, as it happens, it is exceedingly common. Now 
Ross Island is the part of the Settlement that is in immediate inter¬ 
course with Burma and India, and unless it has been imported as a weed 
one can hardly explain its absence from the rest of the Settlement 
where the conditions are quite as favourable for its existence as they are 
on Ross. As regards Galotrojpis too there is a striking fact to record. 
It happens to be the chief food-plant of a particular species of but¬ 
terfly— Danais genutia —which is dispersed throughout India and Burma. 
This buttei-fly was long supposed to be absent from the Andamans, but 
within the past few years it has been sparingly reported thence.* 
It thus seems as if till the establishment of its food-plant in the Settle¬ 
ment this butterfly was not known from the Andamans. To what 
agency the introduction of Danais genutia itself is due it is foreign to the 
purpose of this paper to enquire, but it is a Suggestive fact that once 
the food-plant had become established the butterfly appeared. And the 
absence of the butterfly while there was no evidence of the presence of 
the plant seems pi’esumptive evidence that the plant was not present 
till very recently, and that, therefore, human agency is not merely in¬ 
directly responsible for its introduction, by providing conditions suitable 
for the survival of wind-conveyed seeds, but is directly responsible, from 
the unintentional conveyance of its seeds along with grain or in some 
other way. For it is long since these suitable conditions have come 
into existence, and wind-agency, if a factor at all, is in these latitudes 
a fairly constant one. 
Human agency being so completely responsible, one might hope 
that the channels of introduction of particular species, which must 
coincide with the routes of traffic between the Settlement and the 
adjacent mainland, could be easily ascertained. But this is far from 
being the case. These traffic routes are :— 
* This information was offered by Mr. L. de Niceville in the course of a brief 
conversation that followed the reading of this paper at the meeting of the Asiatic 
Society of Bengal in April 1890. 
46 
