1890.] D. Prain — The non-indigenous species of the Andaman Flora. 255 



But a relative proportion is only less useful than an absolute one 

 would be, and if we take 1000 as a convenient approximation to the 

 actual total we may compare the state of affairs in 1866 with that in 

 1890. In this case we must confine ourselves to introduced phanero- 

 gams only, and exclude the three cryptogams that have been introduced 

 during the interval between 1866 and 1890. The following are the 

 results : — 



76 

 1866. Proportion of introduced to indigenous species = — — or, 1 : 13. 



Percentage of introduced species = -— . or, 7'067o- 



1890. Proportion of introduced to indigenous species = or, 1 : 7. 



„ Percentage of introduced species = or, 12-747o« 



1146 



The greater number of these introduced plants are herbaceous ; but 

 the proportion of woody species is slowly increasing, as the following 

 figures shew : — 



2 

 1866. Proportion of woody to herbaceous species = — or, 1 : 37. 



2 



„ Percentage of woody species = — or, 2*637o' 



7 

 1890. Proportion of woody to herbaceous species = — -r or, 1 : 20. 



7 

 „ Percentage of woody species = — -^ or, 4-797o- 



14d 



Human agency is responsible for the introduction of the whole of 

 this non-indigenous element in the Flora of the Andamans. That it is 

 directly responsible for the introduction of such species as have been 

 intentionally introduced that have subsequently become spontaneous is 

 self-evident ; that it is equally directly responsible for the unintention- 

 ally introduced weeds is hardly less plain. They are with very few 

 exceptions the commonest of Indian road-side and rice-field weeds 

 whose seeds would readily be found mixed with imported grain or 

 attached to the belongings of convict immigrants or of the police sepoys 

 of the Settlement. This mode of introduction explains not only the 

 occurrence of the weeds of dry ground but of the majority of the marsh 

 species, such as Hygrophila, Jussicea^ Ludwigia, as well. And species 

 of the only class for which this explanation is not altogether satis- 

 factory — water-plants like Monochoria^ Ceratopteris, or Ipomcea aqua- 

 tica — nevertheless owe their introduction indirectly to human agency, 



