306 Transactions. — Botany. 



a great many more, and most certainly others must have put 

 in an appearance during a period of more than thirty years. 

 All the same, speaking generally, I do not think introduced 

 plants have taken possession of the soil to anything like the 

 same extent as in hoth Islands of New Zealand. When 

 Chatham Island vegetation is destroyed by fire or cultivation, 

 thus making way for introduced plants, it is certain indige- 

 nous plants which have become weeds rather than those 

 which are introduced. For example, Accena nova-zelandia 

 now abounds everywhere, becoming an actual torment to the 

 pedestrian during certain seasons of the year, one's lower 

 garments becoming completely concealed in a few minutes 

 with a dense brown mass of its barbed fruits Again, the 

 extremely wet character of the soil is antagonistic to the 

 spread of many of those plants which have replaced the 

 vegetation of New Zealand ; while, on the other hand, the 

 shade of the forest demands special adaptations from those 

 plants which seek to get a foothold." Certain plants, how- 

 ever, have spread very considerably. Of such the blackberry 

 {Bttbiis fruticosus) seems to be the only one which is a menace 

 to any large proportion of indigenous plants. At first it 

 was planted for hedges ; but these hedges have now ex- 

 ceeded all bounds and are hedges no longer, but dense 

 thickets. Were this all little harm would accrue, but through 

 the agency of introduced birds the plant is spreading all 

 over the island, especially within the forest areas. I noticed 

 seedling plants in many places, even in the partly primitive 

 tableland forests. On the banks of the Waitangi Eiver are 

 enormous thickets which hang right down into the water ; 

 indeed, in certain places considerable areas are occupied by 

 this plant, and the original vegetation is entirely replaced. It 

 is possible, if the spread of this plant is not checked in some 

 manner or another, it may destroy the forest undergrowth 

 entirely, as well as seize on large areas of open ground. 



Poa pratensis is much valued in Chatham Island as a 

 pasture grass ; it has spread considerably in many places, 

 and has even taken possession of certain stable sand-dunes, 

 covering them with a turf. In wet meadows, such as the 



* Introduced plants spread especially where the indigenous vegetation 

 has been more or less disturbed. Where r,he plant-covering of a region is 

 in its virgin condition, and there is nothing to bring any introduced plants 

 except the wind, they often fail to become established. Thus Mr. T. F. 

 Cheeseman saw only two naturalised species on the summit of Pirongia 

 Mountain (5, p. 321), and these, he writes, " had in all probability been 

 accidentally brought by the surveyors." At the source of the River 

 Poulter, in Canterbury, South Island of New Zealand, I saw no intro- 

 duced plants of any kind in places where man, sheep, or fires had never 

 been, although such country was fully exposed to the north-west wind, 

 which must bring many light "seeds " from Westland (12). 



