Page:Journal of botany, British and foreign, Volume 34 (1896).djvu/367

 THE DISPLACEMENT OP SPECIES IN NEW ZEALAND. 339 and birds which are 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. Kust, 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 off, unless grass-seed is sown immediately, certain species of fungi or of mosses make their appearance, Funaria connivens