1890.] D. Prain — TJie non-indigenous species of the Andaman Flora. 261 



But it is not improbable that by the close of another period equal 

 in length to the second the annual fall in the rate of introduction and, 

 indeed, the annual rate of introduction itself will have become very- 

 small. 



There is not likely to be the same falling off in the rate of naturalis- 

 ation of intentionally introduced species. For, as the Settlement extends, 

 localities suitable for the spontaneous appearance of already introduced 

 species become year by year more numerous and at the same time the 

 number of species capable of naturalisation becomes increased. 



We find on briefly reviewing the results of our enquiry : — 



1. That the total number both of naturalised and of unintentionall}- 

 introduced species constantly increases. 



2. That the rate of naturalisation of intentionally introduced species 

 has hitherto been lower than the rate of introduction of unintentionally 

 introduced species. 



3. That in both cases the rate has been lower for the second period 

 (1866-90) than for the first (prior to 3866). 



4. That this lower rate for the second period is more apparent than 

 real, and is probably due as regards naturalised species to the survival of 

 some cultivated species left to their fate when the early Settlement 

 (1789-92) was abandoned, and as regards weeds to the fact that the 

 greater number of common Indian weeds are necessarily introduced with 

 the earliest sowings of grain. 



5. That in both cases the rate has now probably become nearly 

 uniform, but that while for naturalised species it is steady or even uni- 

 formly increasing, for weeds it is jDrobably uniformly decreasing. 



The firsfc three conclusions are borne out by the facts contained in 

 the lists of species : the fourth is an expression of opinion, which it is 

 unfortunately now impossible either to endorse or to refute as regards 

 the Andamans ; it is, however, a question worthy of attention during the 

 initial stages of any subsequent similar settlement : the last it will be 

 easy for some future student of the subject to finally dispose of. 



In concluding, the writer wishes to express his great obligations to 

 Col. Cadell, v. c ; Chief Commissioner of the Andamans, but for whose 

 kind assistance it would have been impossible to collect so many species 

 during his short stay at Port Blair; also to Dr. G. King, f. r. s., c. i. e,, 

 for his kindness in supplementing the collection of 1889 with many 

 specimens collected in April 1890. 



