THE DISPLACEMENT OF SPECIES IN NEW ZEALAND. 380 



and birds which arc unable to obtain their usual food in the new 

 environment. 



But the space occupied by the displaced plants is not long 

 allowed to remain unoccupied. An army of encroaching weeds 

 speedily takes possession of the vacancy : thistles, star-thistles, 

 docks, groundsels, brambles, briars, and a hundred other un- 

 attractive invaders make their appearance, and increase the 

 severity of the struggle for the survivors of the indigenous flora. 

 From sea-level to the highest points reached by the miner or 

 shepherd, from the North Cape to the Antarctic Islands, their 

 hosts press forward, ever seizing some new position, just as on a 

 larger scale they have long since occupied the vicinity of the chief 

 ports on the great lines of ocean travel from Britain to the Cape of 

 Good Hope, from Yokohama to Cape Horn, so that wherever the 

 traveller lands from his floating home he finds himself surrounded 

 by familiar plants which have in a greater or lesser degree amal- 

 gamated with the vegetation of the country which they have invaded, 

 and which to a large extent they will ultimately overcome. 



And, most unhappily, this invasion is not restricted to phanero- 

 gamic plants. Numbers of injurious fungi accompany their hosts. 

 Eust, mildew, and bunt blight the hopes of the wheat-grower at the 

 moment of fruition. The grazier too often sees his pastures rendered 

 useless by the ravages of smut and ergot ; while the cultivators of 

 edible fruits and vegetables can point to special enemies of almost 

 every kind of plant grown for its value as an article of food. Nor 

 is this all. Numbers of species, almost equally insidious in their 

 development, are parasitic, not only on members of the indigenous 

 flora, but on the naturalized weeds themselves ; so that the circle 

 of infection is constantly widening, while the scientific knowledge 

 and practical skill of the cultivator are taxed to the utmost limit. 



Further, the invading army of plants has brought in its train 

 a still more dangerous host of animals; and as in the vegetable 

 kingdom the most injurious forms were found amongst the less 

 highly organized kinds, so in the animal kingdom the invaders 

 whose agency is most dreaded are members of the Invertebrata : 

 the mussel scale, the fluted scale, the black scale, and many others, 

 together with numerous species of plant-lice, will occur to you as 

 belonging to lowly-developed forms of Insecta. Higher in the 

 scale, the Hessian fly, wire-worm, turnip-fly, and others ; while 

 numerous species of earth-worms, molluscs, birds, and even mam- 

 mals, whether introduced purposely or accidentally, affect alike 

 both fauna and flora. 



Natural Replacement amongst Plants. 



Before considering the injuries sustained by the flora from the 

 numerous naturalized plants, it seems desirable to describe a kind 

 of natural replacement which may be observed to a greater or less 

 extent in nearly all forest districts. On forest or scrub being felled 

 and burnt ofl', unless grass-seed is sown immediately, certain species 

 of fungi or of mosses make their appearance, Fimaria connivens 



