34 PLANTS OF NEW ZEALAND 



we have no large deserts, we could scarcely expect to find in this 

 country the mallee scrub, the myall, the salt-bush and the 

 spinifex of the Australian " bad lands " ; but we might at least 

 have anticipated that forms related to these should occur in 

 New Zealand, modified only by the different conditions obtain- 

 ing here, though their absence may perhaps be explained on 

 the assumption that the specialized Australian forms did not 

 reach the inter-continental bridge, which formerly connected 

 New Zealand with the great northern land-area. 



This answer to the problem may prove to be sufficient, but 

 there is at present no consensus of opinion amongst biologists 

 upon the subject. Dr. Wallace, looking rather to an Aus- 

 tralian than to a Melanesian origin of our flora, has put forward 

 a highly ingenious theory to account for the anomalies observed 

 by Sir J. Hooker. This theory, at one time received tentatively, 

 has more recently been subjected to considerable criticism at 

 the hands of Mr. C. Hedley and others.* On account, however, 

 of its general interest, it will probably be worth while to 

 outline it here, without attempting to form an exact estimate 

 of its value. In Cretaceous times, Australia existed as two 

 islands, an eastern and a western. A wide belt of sea, broken 

 by islets, stretched from the Gulf of Carpentaria to the mouth 

 of the Murray river. The western island, according to Wallace's 

 hypothesis, was the more ancient, and already possessed 

 many of the ancestral forms of the peculiar and character- 

 istic flora of to-day. In eastern Australia, however, the 

 flora consisted chiefly of Melanesian and Antarctic species,, 

 with possibly a small proportion of the more typical Australian 

 forms. About this time, or in the Eocene, the eastern island 

 was united by way of a land-bridge to New Zealand, and 

 by this connection the New Zealand flora obtained its 

 Australian element. Subsequently the eastern and western 

 islands became one, the connection with New Zealand 

 was broken, and the Australian types overran the new 



*Natural Science, September, 1893, p. 187 



