CHAP. XXII.] THE FLOKA OF NEW ZEALAND. 



475 



for all the main features of the New Zealand flora. It shows 

 why the basis of the flora is fundamentally Australian both as 

 regards orders and genera, for it was due to a direct land con- 

 nection between the two countries. It shows also why the great 

 mass of typical Australian forms are unrepresented, for the 

 Australian flora is typically western and temperate, and New 

 Zealand received its immigrants from the eastern island which 

 had itself received only a fragment of this flora, and from the 

 tropical end of this island, and thus could only receive such 

 forms as were not exclusively temperate in character. It shows, 

 further, why New Zealand contains such a very large proportion 

 of tropical forms, for we see that it derived the main portion of 

 its flora directly from the tropics. Again, this hypothesis shows 

 us why, though the specially Australian genera in New Zealand 

 are largely tropical or sub-tropical, the specially Australian 

 species are wholly temperate or alpine ; for these are com- 

 paratively recent arrivals, they must have migrated across the 

 sea in the temperate zone, and these temperate and alpine 

 forms are exactly such as would be best able to establish them- 

 selves in a country already stocked mainly by tropical forms 

 and their modified descendants. This hypothesis further fulfils 

 the conditions implied in Sir Joseph Hooker's anticipation that 

 — "these great differences (of the floras) will present the least 

 difficulties to whatever theory may explain the whole case," — 

 for it shows that these diff'erences are directly due to the history 

 and development of the Australian flora itself, while the resem- 

 blances depend upon the most certain cause of all such broad 

 resemblances — actual land connection. 



One objection will undoubtedly be made to the above theory, 

 — that it does not explain why some species of the prominent 

 Australian genera Acacia, Eucalyptus, Melaleuca, Grevillea, &c., 

 have not reached New Zealand in recent times along with 

 the other temperate forms that have established themselves. 

 But it is doubtful whether any detailed explana^tion of such 

 a negative fact is possible, while general explanations sufficient 

 to cover it are not wanting. Nothing is more certain than that 

 numerous plants never run wild and establish themselves in 

 countries where they nevertheless grow freely if cultivated ; 



