Oliver. — Vegetation and Flora of Lord ffowt Island. 115 



therefore, the case for an early migration along a New Caledonia - New 

 Zealand land line is well supported, while for the New Zealand related 

 species the degree of peculiarity is greatest. 



Endemism. 



Among the causes resulting in endemism two only need be considered 

 here : Firstly, there must ' be effective barriers to the frequent entrance 

 of further members of the same species in order that new variations may 

 not be swamped ; secondly, a sufficient time must elapse for the species 

 to alter in accordance with the changed conditions of the new habitat, 

 and thus degree of peculiarity is roughly an index to the period of isolation. 

 It may perhaps, therefore, be laid down as a working hypothesis that those 

 species longest in the land will comprise the largest proportion of endemic 

 forms and the highest degree of peculiarity, while the presence of widely 

 distributed species indicates that dispersal is probably still going on, and 

 this in the case of an oceanic island leads one to conclude that no direct 

 land connection is required to explain their occurrence. 



The geographical position of Lord Howe Island indicates a considerable 

 lapse of time since it was directly connected by land with any other place, 

 and species that arrived by a land bridge should show a degree of endemism 

 relatively greater than that exhibited by the whole flora. But it is just 

 those which arrived by land that we are endeavouring to discover. The 

 following table is obtained by combining together the figures already given, 

 the figures in the first column including the non-endemic species plus the 

 number shown in the second column. 



These figures might be taken as supporting the hypothesis of a land 

 connection between New Caledonia and New Zealand. The proportion of 

 endemic forms in the Australian element is well below that of the other 

 two regions, though the figures for these latter places probably include 

 species which have actually arrived at Lord Howe Island from the Aus- 

 tralian Continent. In any case, it may reasonably be inferred from the 

 table that arrivals from Australia are more frequent than from Polynesia 

 and New Zealand, and that therefore oversea migration probably accounts 

 for the preponderance of the continental forms. 



Ecological Groups. 

 Dividing the plants into what may be termed ecological groups, and 

 considering these in connection with their geographical relationships and 

 with regard to endemism, brings out some significant facts which will sup- 

 port the conclusions already obtained from other viewpoints. Of fifty- 

 four arborescent and semi-arborescent forest-plants, thirty-eight, or 70 per 

 cent., are endemic. Numerically, Australian forms preponderate, while the 

 New Zealand element is weakest ; but their proportion of endemic forms 

 gives the opposite result. On the face of it this might be construed as 

 indicating that the last land connection was with Australia. But judging 

 from the contour of the ocean-floor this could not be, and the conclusion 



