13 



perhaps most species of New Zealand vascular plants, even 

 those of the high mountains, will only tolerate a comparatively 

 small amount of frost, while not a few, even where they grow 

 wild, are very near their frost-tolerating limit. It may be 

 asserted then, with some degree of confidence, that the climate of 

 these latitudinal boundary-lines, dealt with below, represents the 

 minimum heat-requirement of the species which have their 

 southern limit of distribution in their vicinity. In certain cases 

 this is most likely not the sole deciding factor, but each species 

 would require to be dealt with on its merits. Nor must it be 

 forgotten that the species forming an association are subject to 

 competition and that this also helps to decide what is the mini- 

 mum heat-requirement. The critical parallels of latitude are, 

 36deg.S.,, SSdeg.S., and 42deg.S. This latitudinal distribution 

 concerns only the lowland-coastal flora, the distribution of the 

 high-mountain flora is a more complex matter, for a greater 

 variety of ecological factors is concerned, while the heat-factor 

 is equalized at different latitudes by the gradual lowering in 

 altitude of the various vertical belts of distribution in proceed- 

 ing from north to south. In other words, latitude plays a far 

 smaller part with regard to the high-mountain flora than it does 

 with that of the coast or the lowlands. There is probably no 

 high-mountain plant that, given its other ecological require- 

 ments, especially its water requirement, could not flourish on any 

 New Zealand mountain irrespective of latitude, but, in the low- 

 lands some can grow only under special conditions. This is 

 well-known to the cultivator of New Zealand alpine plants who 

 can grow some with the greatest ease and others with extreme 

 difficulty, while some apparently are impossible to cultivate at 

 all. 



(2) LATITUDE 36 S. AS A PHYTOGEOGRAPHICAL BARRIER. 



A considerable number of species occur only to the north 

 of lat. 36deg.S. ; and, as some of these are restricted to the far 

 north of the island and others do not nearly reach the above 

 parallel, this is not so much a "barrier" as a dividing line 

 between two phytogeographical divisions. This was originally 

 pointed out by Colenso in his classical essay 13 written so early 

 as 1865, and he distinguished north of that latitude two botani- 

 cal areas, namely, "The Northern Area" (34deg.S. to SSdeg.S.) 

 and "The Bay of Islands area" (SSdeg.S. to 36 deg.S.). The 

 following is a list of the species: (Lycopodiaceae) Lycopodium 

 Drummondii; (Filices) Asplenium japonicum, Todaea barbara; 

 (Gramineae) Microlaena Carsei; (Cyperaceae) Cladium 

 complanatum, Lepidosperma fill forme; (Centrolepidaceae) 

 Hydatellainconspicua; (Orchidaceae) 1 * Thelymitra intermedia, 



13. On the Geographic and Economic Botany of the North Island of New 

 Zealand. Trans. N.Z. Inst., vol. i, 2nd Ed., pp. 233-283, 1876 (written for the 

 New Zealand Exhibition, 1865, and published in the 1st Ed. of the Trans. N.Z. 

 Inst in 1870). 



14. When the distribution of the terrestrial orchids of New Zealand is better 

 known, doubtless some of the orchids listed here will be found to have a wider 

 range. 



