ON THE 



GEOGRAPHICAL BOTANY OF NEW ZEALAND. 



EXPLAKATOET OF A SeBIES OF ESSATS BY 

 SIR DAVID MONEO AND MESSES. TEAVEES AND BUCHANAN. 



BY JAMES HECTOE, M.D, F.E.S. 



(Plate V.) 

 l^Head hefore the Wellington Philosoj>7iical Society, loth Septemher, 1868.] 



In commumcating the following essays, I will take the opportunity of 

 explaining briefly, by a single example, the chief physical peculiarities which 

 regulate the distribution of the vegetation in the South Island. 



The accompanying diagram (pi. V.) is an ideal section across the island, 

 between latitudes 40° 30' and 46° 30' S. The greatest altitude met with in such 

 a section will be 10,000 feet, but the mean elevation of the ridges that 

 connect the various summits is barely 5,000 feet, while in these occur breaks, 

 or "passes," in the mountain chain, which, by permitting the passage of the 

 western winds, give rise to local modifications of the flora at the points 

 where they lead out on the eastern slope. The best known of these are the 

 pass from the head of the Wanaka Lake, by which Dr. Haast crossed to 

 Jackson Bay ; and the Grreenstone Pass, leading from the "Wakatipu Lake to 

 Martin Bay. Another pass, only a few miles in length, crosses the narrowest 

 part of the Southern Alps, between the head of the sounds and arms of 

 Te Anau Lake. , 



These breaks in the mountain chain have all about the same altitude of 

 less than 2,000 feet above the sea level, which is sufficiently low to admit of 

 the transfusion of many species of plants. 



Erom the fact that these passes follow longitudinal valleys with a 

 succession of short gorges at right angles to their general course, and do 

 not coincide with straight transverse depressions, the influence Avhich in 

 the latter case they would have exercised on the climate of the interior is 

 greatly reduced ; nevertheless, the mild and genial climate that is experi- 

 enced in the neighbourhood of the "VYanaka and Wakatipu Lakes, is to be 

 attributed, in a great measure, to the existence of these deeply-cut notches 

 in the mountains. 



