Page:Journal of botany, British and foreign, Volume 34 (1896).djvu/370

 342 THE DISPLA.CEMENT OF SPECIES IN NEW ZEALAND. In a few localities goats have been equally destructive. I have been informed that the tainui [Pomaderris apetala) has been completely destroyed at Kawhia, where it was formerly abundant, and is now restricted to the south head of the Mokau River and the Chatham Islands. Injury caused by Rats. Some plants formerly plentiful have been to a large extent destroyed by the pig and the rat, as the curious orchid, Gastrodia Cunninghamii, the tubers of which are highly nutritious. This plant has become very rare in districts where the black rat is plentiful. On one occasion, in 1874, I found three remarkably fine specimens, quite 2 ft. in height, with tubers 6 in. or 7 in. in length, and placed them in what seemed a safe place in a hut at Omaha, but during the night they were carried off by the rodents, Both the pig and the grey rat feed upon the fleshy roots of the larger JJmhellifera. Injury caused by Insects. A small native beetle, which I have not been able to identify, has greatly reduced many species of Celmisia and other Cornposita by depositing its eggs on the disc florets, where they quickly enter the larval state, and destroy the carpel before it reaches maturity. The great increase of this insect during recent years is doubtless caused by the frequent burning of the surface vegetation, and con- sequent destruction of the lizards and predatory insects which kept the beetle in check. Several species of Diptera which are equally destructive doubtless owe their rapid increase of late years to the same cause. Displacement by Introduced Plants. In many instances a comparatively few species of naturalized plants have taken possession of sea-beaches, completely displacing the original vegetation by their more vigorous growth and their vast numbers — simply crowding it out by depriving it of air and light, and to a large extent absorbing its nourishment. This may be seen, for instance, south of the township of Kaikoura, where a broad stretch of land at the water-margin is wholly given up to such weedy plants as the common brome-grass [Bromus steiilis), docks {Fuunex obtusifolius, B. crispus, &c.), fleabane (Erigeron cana- densis), catchfly {Silene anglica), Yorkshire-fog {Holciis lanatiis), and others, perchance intermixed with one or two native plants of similar habit. Here the displacement is almost complete, the original littoral vegetation having been driven to a few peculiarly favoured spots, where it maintains a somewhat precarious existence. The displacement of the New Zealand flax {Phormium tenax), the coarse sedge known as toe-toe- whatu-manu {Cyperus ustidatus), and the common fern {Pteris esculenta), by European grasses and clovers is so striking that it has arrested the attention of the natives, and, indeed, it is calculated to attract the notice of even a casual observer, for the indigenous species mentioned are so robust that the mere idea of their being overcome in the struggle for existence by such plants as clovers and grasses seems almost absurd :