Page:Journal of botany, British and foreign, Volume 34 (1896).djvu/371

THE DISPLACEMENT OP SPECIES IN NEW ZEALAND. 843 but the fact remains. Seeds of rye-grass, meadow-grass, white or red clover, &c., germinate by the side of the coarse-growing toitoi, and gradually abstract the moisture which it has been enjoying undisturbed ; the growth of the sedge becomes less vigorous, while that of the interlopers is more robust. The result would not be in doubt were the plants now left undisturbed, but an overpowering force comes to the help of the invaders — the rich grass attracts cattle and horses to graze upon it ; this increases the vigour of the grass, while the native plants have to contend against the consolidation of the soil caused by the trampling of heavy stock ; this further invigorates the interlopers, and enables them to con- tinually extend their area by giving off new shoots from the base, and occasionally by producing seed. As their growth increases the vigour of the toitoi perceptibly diminishes, and its ultimate ex- tinction is certain, although the process may occupy several years. The occasional replacement of manuka (Leptospermum scopariiim) and other shrubs by grasses is still more striking. Sir George Grey drew my attention to this fact on my first visit to the Kawau, in 1864, where the naturalized Sporoholus indicus was spreading amongst manuka from 5 ft. to 8 ft. in height, forming a sward which, notwithstanding the coarse character of the herbage, was closely cropped by stock, to the benefit of the grass and injury of the shrub. But even this is less surprising than an instance of a similar kind at the Bay of Islands, where a delicate and slender naturalized love-grass [Eragrostis Brownii) is exerting the same influence on a large scale. Introduced grasses exhibit similar action upon many native grasses in all parts of the colony and at all elevations. In the Upper Waimakariri, Triodia exiyua often forms a compact and extensive sward, which is usually able to resist aggression on the part of its indigenous allies ; but if a single grain of rye-grass [Loliiim 'perenne) or meadow-grass {Poa prateiisis) falls amongst it and germinates, the continuity of the sward is speedily interrupted, and a process of disintegration sets in which ultimately destroys the whole, or reduces it to small tufts or patches. The same result is often exhibited at the expense of more robust plants. The gradual replacement of the Spaniard [Aciphylla Colensoi) by self-sown pasturage plants is most remarkable. It seems next to impossible that the large rigid bayonet-like leaf- segments which surround the base of the flower- stem in this strange plant should be injured by a growth of soft herbs, however compact ; yet, so it is : dense masses of the Spaniard, actually impenetrable to stock of any kind, are destroyed by this simple agency. When once its vigour is reduced the ultimate destruction of the Spaniard is simply a matter of time. The common spear-grass [A. squarrosa) is often displaced in the same way. Amalgamation of Native and Introduced Plants. But there is another aspect to the case ; for, however remarkable it may seem after the statements that have just been made, certain slender native grasses, of great value on account of their nutritive qualities, are able to resist the invaders, and ultimately become