Cockayne. — Ecological Studies in Evolution . 33 



invader can replace the aboriginal.* On the other hand, although this 

 foreign host is present in its millions, and notwithstanding abundant winds 

 and land-birds, f the indigenous vegetation is still virgin and the introduced 

 plants altogether absent where grazing animals have no access and where fires 

 have never been. On certain subalpine herb-fields the indigenous form of 

 the dandelion (Taraxacum officinale Wigg.) is abundant, and yet the in- 

 troduced form, with its readily wind - borne fruit, has not gained a foot- 

 hold, nor even the abundant Hypochoeris radicata L., though it may be in 

 thousands on the neighbouring tussock pasture, less than one mile away. 

 On Auckland Island introduced plants occur only in the neighbour- 

 hood of the depots for castaways, but on Enderby Island, where there are 

 cattle, they are much more widely spread. Even where the rain forest 

 has been felled or burnt, and cattle, &c, are kept away, it is gradually 

 replaced by indigenous trees and shrubs — i.e., in localities where the rain- 

 fall is sufficient. 



Some of the indigenous species are quite as aggressive, or even more 

 so, than any of the introduced. In primeval New Zealand each would have 

 its place in the association to which it belonged — there would be no aggres- 

 sion ; but when the balance of nature was upset by the fire or cultiva- 

 tion of Maori or European, then the plants best equipped for occupying 

 the new ground become dominant, their " adaptations " for that purpose 

 fortuitously present. The miles on miles of Leptospermum scoparium and 

 Pteridium esculentum were absent in primitive New Zealand. So, too, the 

 pastures of Danthonia semiannularis R. Br. J in Marlborough, and the many 

 acres of Chrysobactron Hookeri Colenso (Liliac.) in the lower mountain 

 region of Canterbury. Celmisia spectabilis Hook, f., an apparently highly 

 specialized herb for alpine fell-field or tussock-steppe conditions, is now 

 on the increase in many montane parts of the Ashburton-Rakaia mountains 

 and valleys, owing to its being able to withstand fire, the buds being 

 protected by a close investment of wet decayed leaf-sheaths. 



Nor are all the introduced species aggressive, by any means. Some 

 can barely hold their own ; others are limited to certain edaphic condi- 

 tions. Thus, Glaucium, flavum Crantz occurs, as yet, only on the coast 

 of Wellington, chiefly in the neighbourhood of Cook Strait. It is con- 

 fined to gravelly or stony shores, and appears unable to grow on the clay 

 hillside. And yet where the latter is, in one place near Lyall Bay, covered 

 with gravel there is a large colony of the plant, whence none have found 

 their way on to the adjacent hillside. Lupinus arboreus, now so common 

 on New Zealand dunes, appears unable to spread beyond the sandy ground. 



The often-quoted stories (see footnote, p. 32) of white clover (Trifolium 

 repens L.) being able to wipe out Phormium tenax, of Salix babylonica over- 

 coming the watercress (Radicula Nasturtium-aquaticum), of Hypochoeris 



* New Zealand may be roughly divided into three areas — viz., the cultivated, the 

 pasture lands, and the primitive. It is only in the pasture lands that a real struggle 

 between the introduced and the indigenous plants is taking place, and even there the con- 

 test is very unequal, through the grazing, burning, and seed-sowing factors. Many 

 pastures, however, are altogether new associations, as in the case of forest being felled, 

 then burned, and the ground sown with grasses, &c, even before the ashes of the tree* 

 are cooled, so that at once there is a foreign pasture brought into existence and subject 

 to an entirely new set of conditions from that which governed the forest. This is certainly 

 not biological " replacement." 



f Introduced, not native, birds. 



% The species may be D. pilosa, but I have no specimens for identification. 



2— Trans. 



