1890.] D. Prain — The non-indigenous species of the Andaman Flora. 259 



The rate per annum for the second period requires a slight correction 

 by the deduction from it of the rate per annum of disappearance of natur- 

 alised species. We have seen that one introduced plant occurring. spon- 

 taneously in 1866 was only under cultivation in 1889 and 1890 and that 

 three of the 1866 weeds were not met with in 1889 or 1890. These 4 

 species, therefore, give a disappearance rate of ■£$ = %, or 0'16 species per 

 annum, and the corrected rate for Period II is thus 3'28 — 0'16, or 3'12 

 species per annum. 



When we find on comparing the two periods that the rate of in- 

 troduction in the second is only 3' 12 species, as compared with 6"90 in 

 the first, we naturally endeavour to find some explanation of the dis- 

 crepancy. But, unfortunately, no very satisfactory explanation offers 

 itself. So far as cultivated species are concerned, we are not in a posi- 

 tion to compare the 15 naturalised species of 1866 with the 23 similar 

 species of 1890, but only with those 9 species that had been both intro- 

 duced and naturalised subsequent to 1866. The pi'oportions indicated 

 by these two classes being 1'36 : 37 evidences a rate of naturalisation 

 per annum 3| times as great for the earlier as for the later period. But 

 when the circumstances of the case are considered we are not surprised 

 that the difference should be so great ; we are, rather, astonished at its 

 being so small. Owing to the abandonment of the 1789 Settlement the 

 species that had been introduced while it existed were left to their fate, 

 and it would be no more than reasonable to expect that when the new 

 Settlement was founded in 1858, and when Mr. Kurz visited it in 1866, 

 the majority of the common tropical cultivated species had already be- 

 come fairly naturalised. So far, however, was this from being the case 

 that we find there were in 1866 only 15 such species naturalised, and 

 we are compelled to conclude either, that the oiuginal settlement was 

 very ill provided for, or that the species which on a priori grounds we 

 might consider likely to hold their own in the struggle for existence in 

 an abandoned settlement are really far from being able to do so. Now 

 not only is there no ground for supposing that the Settlement was ill- 

 provided for, but there is ample proof, from the evidence that exists of a 

 direct and extensive reciprocal correspondence between its founders and 

 the first Superintendent of the recently established Hon'ble Company's 

 Botanic Garden at Calcutta, that the number of species introduced at Port 

 Cornwallis was, for a Settlement so young, unusually high. We are com- 

 pelled, therefore, to accept the other explanation and to conclude that 

 cultivated species are not as a rule able to exist when they have to 

 struggle on equal terms with a native jungle. Without mentioning other 

 instances, we may refer to the lists of Cucurbitacece and Leguminosce pre- 

 sent in 1866 as cultivated plants only, yet in 1890 beginning to occur 

 34 



