256 D. Prain — The non-indigenous species of the Andaman Flora. [No. 3, 



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 mo3t probable being the Selaginella and the Gheilanthes, — 

 almost the only posssible one among phanerogams being the Oalotropis. 

 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 Oalotropis too thei'e 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 butterfly 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 buttei^fly appeared. • And the 

 absence of the butterfly while there was no evidence of the presence of 

 the plant seems presumptive 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 wag 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. 



