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 multiflora, a North American malvaceous plant, an Australian Plantago, two species of Erigeron, and Kyllinga. The rat-tail grass, too, is no doubt introduced, and has been most aggressive, while the South African Cyperus (minimus?) is nearly as ubiquitous as sorrel. (3.) The agency of birds in scattering seeds is most noticeable 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 spreading—e.g., Haloragis tetragyna, H. minuta, Aristotelia racemosa, 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 Hypochæris 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 neighbouring 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 (5,500 ft.), 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.