Thomson. — Plant-acclimatisation in New Zealand. 323 



•characters of North European plants is decided enough, but 

 many non-European plants are now widely spread here, and 

 are, indeed, very aggressive. I may instance Modiola multi- 

 flora, a North American malvaceous plant, an Australian 

 Plantago, two species of Erigeron, and Kyi ling a. The rat-tail 

 grass, too, is no doubt introduced, and has been most aggres- 

 sive, while the South African Cyperus {minimus'}) is nearly as 

 ubiquitous as sorrel. 



(3.) The agency of birds in scattering seeds is most notice- 

 able here (Auckland). The Cape gooseberry, the blackberry, 

 and the inkweed {Phytolacca) are now spread over vast areas 

 entirely through their agency. 



(4.) Here, as in the South, a few native plants are spread- 

 ing — e.g., Haloragis tetragyna, H. minuta, Aristotelia race- 

 mosa, Fuchsia excorticata, Pomaderris phylicifolia, Erechtites, 

 &c. ; but the most aggressive plant of all is Pteris aquilina, 

 which is rapidly overrunning much of the land that has been 

 cleared of bush, and which permanently establishes itself 

 before roots are sufficiently decayed to admit of ploughing. 



(5.) I suppose our most abundant and most widespread 

 introduced weed is Hypochmris radicata. This furnishes a 

 good example of the mode in which an aggressive plant 

 spreads. Its seeds germinate easily, the roots strike down to 

 the moist layer promptly, the rosulate leaves keep neighbour- 

 ing plants from encroaching on it when established, and the 

 seeds when mature are wafted afar by the wind. Add to 

 this that cattle and horses will not touch it, and its rapid and 

 universal diffusion calls for no special constitutional vigour. 

 The specific advantages thus assigned sufficiently account for 

 its spread. I do not know of any reason for thinking its 

 seeds possess long vitality, but in spite of this drawback it 

 has advantages enough to fully explain its predominance. 

 We found it on the topmost rock of Mount Hikurangi 

 (5,500ft.), on the east coast, where the wind must have 

 brought it from many miles' distance. It was the only weed 

 that we noticed on that mountain, a region which has 

 never been reached by cattle, sheep, or horses, and has never 

 been overrun by fire. Again, take the case of sorrel. It is 

 widely spread by seeds, which are eaten but not injured or 

 digested by grazing animals, and it spreads by underground 

 runners with great quickness. It forms large tufts of foliage 

 that keep off or smother competitors in grazed land. These 

 facts seem to me enough to account for its spread without 

 postulating any special constitutional vigour. Most other 

 cases of aggressive plants are, I think, to be accounted for by 

 special advantages of habit and growth, and these are matters 

 that will well reward studious inquiry. 



