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eludes not only the soil proper (from rock to ordinary soil), but 

 also water. With the soil are included the gases and water 

 which it contains. It is this edaphic factor, in conjunction 

 with the local climate, which chiefly governs the habitats of the 

 associations and the growing places of the species. A consider- 

 ation of plant-distribution on edaphic lines would open up the 

 whole of the ecology of New Zealand plants a vast field as yet 

 but superficially explored. All that can be attempted here is the 

 statement of certain generalities together with an account of a 

 few cases where the effect of the soil is clearly apparent. 



Generally, in New Zealand, the nature of the underlying 

 rocks has apparently but little influence on plant-distribution. 

 Rain-forest consists of the same species, at similar latitudes and 

 altitudes, whether the underlying rock be greywacke, volcanic, 

 limestone, or schist. That familiar sight, cliffs or steep banks 

 covered with the great leaves of Blechnum capense is in evidence 

 both on the calcareous mudstone declivities of the Wanganui 

 River and on ancient moraines of Southern Westland. The 

 Olearia insignis association, already referred to, thrives equally 

 well on either limestone or greywacke. There are fine forests 

 of Podocarpus totara both on the volcanic hills of Banks 

 Peninsula and on the pumice of the Volcanic Plateau. 



Taking the case of limestone, it is true that a few species 

 (Asplenium lucidium var. anomodon, Anisotome palula, Senecio 

 glaucophyllus) have been recorded from limestone rocks only, 

 but so far as I know, limestone and greywacke, side by side, bear 

 exactly the same species. Still, more detailed research might 

 reveal certain constant distinctions between the vegetation of 

 limestone and that of non-calcareous rocks. 



With one or two exceptions, to be noted presently, it is not 

 the chemical constitution of soils in New Zealand which deter- 

 mines the species, or plant-associations, but their physical 

 condition and, above all, their water-content. Thus stony river- 

 bed in the wet climate of Westland may carry forest, while in the 

 drier eastern climate there is merely an open vegetation of 

 species of Raoulia and Epilobium, to be finally replaced by low 

 tussock-grassland or xerophytic shrubland. 



Stony debris slopes in the high mountains, so long as they 

 are not subject to an excessive rainfall, have a remarkable 

 number of plants in common many of which, in their growth- 

 forms, stand in special categories to themselves. As with 

 forest in its area of distribution, so with tussock-grassland, that 

 of the South Island extends for hundreds of miles, covering 

 many classes of soils and exposed to many local climates, but 

 the dominant tussocks remain the same, e.g., Poa caespitosa 

 and Festuca novae-zealandiae, or where the soil is sour, usually 

 at higher altitudes, Danthonia flavescens or D. Raoulii in their 

 various varieties. In both these cases (forest and grassland) 

 the formation, as a whole, is governed by climate, but its changes 

 in structure depend upon the edaphic factor. The poa and fescue 

 tussocks, when both occur, indicate respectively the wetter and 

 the drier ground. 



