G. M. Thomson. — On the Origin of the New Zealand Flora. 491 



Stated concisely, his conclusions are that for a long period of time Aus- 

 tralia was divided into two islands, a western and an eastern. In the 

 former of these, the peculiarly characteristic Australian genera, both of 

 plants and animals, originated. The eastern island stretched in a long 

 narrow line from the tropics to the south of Tasmania, and in connection 

 with its tropical portion there was probably a prolongation of New Zealand 

 to the north-west. By this bridge, with its southerly and south-easterly 

 ramifications, a stream of immigrants set in from the tropical regions 

 further north, so that numerous genera and even species of plants, as well 

 as some animals, were spread along both shores of the sea separating New 

 Zealand from Australia. The subsequent depression of the northern area 

 caused a separation of New Zealand from tropical Australia, while the 

 elevation of the comparatively shallow sea separating the western from the 

 eastern island, united these two into the great continental island of Aus- 

 tralia, over the whole of which the peculiar western forms spread rapidly, 

 and apparently at a much greater rate than the tropical and eastern species 

 did. While the presence of the Australian, Asiatic, and Polynesian elements 

 in the New Zealand flora are traceable to this former land connection, the 

 antarctic and South American forms are believed to be due to immigration 

 from outlying islands and extensions of land to the south, and the Euro- 

 pean, or more correctly the arctic element, is explained by the extraordin- 

 arily aggressive character of the so-called Scandinavian flora, which has 

 enabled it to push its colonists over the three great southern areas, viz., 

 South Africa, South America and Australasia. 



Mr. Wallace's explanations of the origin of om- flora must commend 

 themselves as extremely satisfactory to every one capable of judging of the 

 questions under consideration. Our subsequent knowledge may modify 

 some of his conclusions to a slight extent, but it is by the publication of 

 such hypotheses and theories, and the application of them for the solution 

 of difficult problems, that correct ideas are most rapidly attained. Not 

 only is our interest heightened by such speculations, but definite issues are 

 placed before our minds, and we are enabled to judge more and more accur- 

 ately of these, and to recognize how vast the field to be traversed is. It is 

 well to bear in mind that as our stock of facts increases, so also does our 

 knowledge of our ignorance, and that the latter often increases in a much 

 more rapid ratio than the former. We begin by discussing a limited ques- 

 tion, satisfied perhaps that we have sufficient information accumulated to 

 enable us to give a definite answer, but at every turn collateral points are 

 raised, until at last we feel ourselves face to face with an overpowering mass 

 of questions all demanding solution, and are at the same time conscious of 

 our inability to grapple with them. But it is only given to the few — to a 



