346 



THE DISPLACEMENT OF SPECIES IN NEW ZEALAND. 



Europe. Twigs of these trees are easily detached, and are floated 

 by the river to new situations, where they quickly take root and 

 develop with rapidity, so that in certain situations navigation is 

 impeded. 



Introduced Plants on Broken Soil. 



Introduced plants compete with indigenous species for the pos- 

 session of any newly-loosened surface, and especially for waste land. 

 The margins of newly-formed roads are speedily clothed with a 

 dense growth of sheep's-cress, docks, thistles, Yorkshire-fog, and 

 many others, mixed with the native piripiri [Acana samiiiisorhce), 

 toad-grass {Jimcus biifoniiis), Danthonia semi-annularis, and when 

 neglected form splendid nurseries for injurious insects and fungi. 

 Crumbling places on hillsides in many localities are quickly covered 

 with a strong and permanent growth of the blessed-thistle [Silylum 

 ]\I((ria)iHi»), which distributes vast quantities of seeds, and over- 

 comes indigenous and introduced plants alike, forming continuous 

 masses of variegated foliage in the early spring, but presenting a 

 ragged and untidy appearance during the autumn and winter 

 months. The common spear-thistle (Cniais lanceolatns) furnishes 

 a striking example of the ability of a plant to seize upon situations 

 suitable for its growth ; in many districts immediately after the 

 bush is burnt off the entire area is overrun by this rapacious invader, 

 which exhibits a dense luxuriant growth often 4 ft. to 5 ft. high, 

 preventing the growth of grass, and forming an almost impenetrable 

 mass. The growth becomes less luxuriant during the second season, 

 so that the grass is able to make headway, and by the end of the 

 fourth season only a few old thistles have retained sufficient vigour 

 to reassert themselves. The so-called Californian thistle (C. arvensis) 

 is the only naturalized species capable of injuring pasturage to any 

 serious extent, and, unhappily, it is often the cause of serious loss 

 to the pastoralist and agriculturist. The Gundagai thistle, as it is 

 called in New Zealand [Canbais pycnocephaius), flourishes on newly- 

 disturbed soil in many localities, but is comparatively rare on 

 grass-land. 



Whenever the finely-comminuted basaltic scoria of the Auckland 

 isthmus is disturbed, a luxuriant crop, chiefly of naturalized plants, 

 speedily makes its appearance, but amongst them one of the most 

 abundant is the indigenous Chenopodium carinatum, although not a 

 specimen may have been seen in the vicinity until the surface was 

 disturbed. After the second year the number of plants is greatly 

 diminished, and during the fourth year only solitary specimens are 

 to be found. A similar instance has been observed at Cape Whan- 

 brow, near Oamaru. Whenever the fine silt which covers the surface 

 is disturbed, Lepidiiim tenuicaxde and the indigenous form of Atriplex 

 patida make their appearance in abundance, although usually both 

 plants are only to be found in small quantity. 



Naturalized Aquatic Plants. 



The increase of the watercress {Nasturtiwn amphihium [officinale] ) 

 in streams and watery places is phenomenal, and attracts the 

 attention of new arrivals on account of the excessive luxuriance 



