12 



becomes a bad weed in both areas after forest is destroyed (see 

 Fig. 6) ; Dysoxylum coastal-forest is a well-marked feature; 

 Muehlenbeckia Astoni a plant of extremely limited distribution 

 occurs at the mouth of the R. Ongaonga (Wellington) and 

 near the mouths of the Awatere and Flaxbourne Rivers (Marl- 

 borough) ; finally, the introduced Glaucium flavum occurs on 

 shingly beaches on the northern shores of Cook Strait and at 

 the mouth of the Awatere. To be sure there are some differ- 

 ences of minor importance One of some moment, however, 

 may be cited. This is the abundance of Arthropodium cirratum 

 on coastal rocks in the Marlborough Sounds; in the North 

 Island, I do not know of its occurrence except in the Auckland 

 Botanical Districts. Other localities for this species are 

 Stephen's Island (Cook Strait), Takaka and West Wanganui 

 Inlet (Nelson). 



Against all that has just been said, it may be urged that 

 Cook Strait has proved a formidable barrier for the high- 

 mountain plants to overcome as proved by the much smaller 

 high-mountain flora of the North Island. But I may again 

 point out that the poverty of this flora is due in part, at any 

 rate, to the limited space available for alpine and subalpine 

 plants in the North Island. Certain common North Island 

 subalpine plants are present, however, only on the Nelson 

 mountains, but do not extend further south. Such are Celmisia 

 hieracifolia, Leucogenes Leontopodium, Ranunculus insignis 

 .(see Fig. 8), R. geraniifolius and Senecio Adamsii. To these 

 may perhaps be added Senecio elaeagnifolius var. Buchanani 

 which occurs on Mount Stokes (Marlborough Sounds) and 

 Ourisia macrophylla which extends south as far as the Seaward 

 Kaikoura and Hanmer Plains mountains. The North Island 

 high-mountain flora consists of about 175 species and of these 

 about 142 are also South Island species. Probably for a long 

 period North and South Island mountains have been separated 

 by forest, so that the settlement upon a North Island mountain 

 of a species coming from the south would be a matter of 

 difficulty. 



(b) The relation of latitude to distribution. 



(1) GENERAL. 



New Zealand proper extending, as it does from about latitude 

 34deg. S. to about latitude 47deg. S., offers an excellent example 

 of the effect of change of temperature upon the distribution of 

 the lowland-coastal flora and vegetation. It will be seen from 

 what follows that near certain parallels of latitude there are 

 critical belts on, or near which, species more or less common 

 further north come to a halt. This does not say that such 

 species could not exist further to the south. On the contrary, 

 cultivation has proved that many of them are hardy in gardens, 

 etc., far to the south of their natural area of distribution. The 

 kauri (Agathis australis), the puriri (Vitex lucens), the nao 

 (Colensoa physaloides) and the puka (Meryta Sinclairii) are 

 cases in point. Nevertheless, it is well-known that many 



