848 THE DISPLACEMENT OF SPECIES IN NEW ZEALAND. of species is certainly over five hundred, as already stated. Making all fair allowance for the imperfection of the records for 1855 and 1869, it will be seen that naturalized species have increased with great rapidity during the last fifty years. But it is not probable that this rate can be maintained ; the number of encroaching species suitable for a given habitat, after all, must be limited, and it may well be that the limit for New Zealand, so far as introductions from European countries are concerned, is very nearly reached. As bearing upon this point, it may be remarked that, as many of the naturalized plants of dififerent countries are migrants from a com- mon centre, a large proportion must necessarily be identical ; for instance, out of 243 species enumerated by Mr. C. Moore, F.L.S., as naturalized in New South Wales, fully three-fourths are natu- ralized in New Zealand also ; the remainder, consisting chiefly of plants from warmer countries, are not capable of becoming naturalized here. Again, out of 103 species of plants recently introduced with ballast from Buenos Ayres, eighty-six were already naturalized here. The distribution of naturalized plants in the colony follows to a very great extent the same lines as those of the indigenous flora : the number of species decreases rapidly southward. Upwards of four hundred and twenty species are found in the Auckland District, but no other district in the colony contains so large a number ; less than three hundred species would be found in the Wellington District. It must, however, be remembered that the climate of Auckland is much more favourable to the naturalization of plants from warm temperate climates than that of any other part of the colony. A singular illustration of this has been recently given. A large quantity of ballast taken on board at Buenos Ayres was discharged at Wellington from a vessel loading for Europe. Over a hundred species of plants made their appearance on the ballast before the close of the second summer, the great majority being plants already naturalized in the Auckland District ; twenty-seven species, however, had not previously been observed in Wellington, and of these seventeen species had not previously been seen in any part of the colony. In all probability not more than two of these will become naturalized — most likely only one. But had the ballast been deposited on the light scoria soil of the Auckland isthmus instead of on the stiff Wellington clay, it is absolutely certain that in the absence of interference fully one-third would have become established — probably more. I will only add, as an additional reason for not expecting so large an increase in the number of introductions as formerly, that during the last fifteen years great improvements have been made in cleaning garden-seeds, agricultural seeds, and cereals, which will not only tend to reduce the number of species likely to be introduced in the future, but to prevent the yearly importation of certain species which at present are but partially naturalized. Chiefly from this cause certain species, such as Fumaria officinalis, Lepidium campestre, Papaver Rhceas, Githago segetum, Scandix Pecten-veneris, are less plentiful in many districts than they were twenty years ago.
