FKOM AX OLD STANDPOINT. 



181 



As illustrating the results of the diherent ageiicies of 

 dispersal in the same region, I will take the case of the 

 Tahitian <^von\) in the mid-Pacihc, niakino- use of the data 

 p^iven in my l)Ook on Plant- Di'ipcrsaL The observations of 

 Dr. Treub and of Prof. Penzig on the stocking of Krakatoa 

 with its plants justify us in assuming that the agency of wind 

 in mid-ocean would be almost entirely confined to the transport 

 of the spores of cryptogams. On the other hand the observa- 

 tions of many observers have shown that the agency of birds 

 is restricted mainly to the inland flowering plants and the 

 agency of currents to the shore plants. The effect of these 

 agencies on the difi'erentiating process of the plants concerned 

 is of course displayed in the degree of endemism, or in other 

 words, in the proportion of peculiar species. It thus appears, 

 as is clearly indicated in the case of the Tahitian Islands in 

 the accompanying table, that the difterentiating process has 

 been much more retarded where eitlier the winds or the 

 currents have been the agents of dispersal tlum where the 

 l)irds have been the agents. Among the shore-plants, which 

 are mainly dispersed by the currents, only 1 or 2 per cent, of 

 the species are peculiar, and amongst the wind-dispersed ferns 

 and lycopods 8 per cent, are peculiar, whilst amongst the 

 inland flowering plants as many as 43 per cent, are confined 

 to the group. In the Hawaiian Islands, where the isolation 

 has been markedly greater than with the Tahitian group, SO per 

 cent, of the flowering plants and 45 per cent, of the vascular 

 cryptogams (ferns and lycopods) are peculiar, the true littoral 

 Mora being very scanty, owing to the position of the islands 

 witli regard to the currents. 



TaUe illustrating the relation hctween the proportion of peculiar 

 species in thr Tahitian flora and the mode of disp'^r.^al. 



Station and C^liaracter. 



Prevailing 

 mode of 

 dispersal. 



Total number 

 of species. 



Proportion of 

 peculiar species. 



Coast flowering plants 



Cnrrents 



55-60 



1 or 2 per cent. 



Ferns and lycopods ... 



"Winds 



154 



8 per cent. 



Inland floweringplants 



Birds 



260 



43 per cent. 



