October 7, 1887.] 



SCIENCE 



171 



very much, and coincidently with this has been such a decrease in 

 the Aphis, that it has practically ceased to be a pest. 



But the most conspicuous effects of man's influence is the intro- 

 duction of numliers of species of plants which find themselves more 

 ■or less at home in this new land. It is matter of common remark 

 to every person coming to the colony, how English every thing 

 looks. The wayside weeds, the grass with its daisies and ox-eyes, 

 the fields and gardens with European chickweed, docks, and 

 thistles, — all remind him of the old land. English plants chiefly 

 have spread themselves over the country, wherever the settler has 

 gone. One might expect that Australia, or America, being so 

 much nearer, would have furnished the greatest proportion of im- 

 migrants ; but this is not found to be the case. It is what Sir 

 Joseph Hooker has called the aggressive Scandinavian flora, which 

 so strongly asserts itself on all sides. The reasons of this are per- 

 haps not far to seek. Nearly all the seeds brought to the colony 

 in the earlier days of settlement came from Britain. English 

 grasses were brought and sown down, and along with them came 

 the weeds of English pastures. Compressed hay was brought 

 frequently with imported stock ; straw-packed goods were, and 

 are, scattered throughout the country ; and thus, in one way and 

 another, it is the European species of weeds which have found their 

 way here in the greatest abundance. The conditions of acclimatiza- 

 tion are very dissimilar in different parts of the colony, extending 

 as it does through twelve degrees of latitude, and thus embracing 

 ver)- different climates. The southern parts of the South Island 

 are as different from the Bay of Islands as Scotland is from Italy. 

 Throughout the greater part of the east side of the South Island, 

 night frosts are experienced during the winter, even along the coast ; 

 while inland the cold is much more intense' and continued, the 

 summer being at the same time hotter. But in all other parts, 

 frost, at ordinaiy levels, is the exception, while in no portion of the 

 country are the droughts prolonged, as in Australia. 



One of the results of such a distribution of climate is, that fewer 

 introduced plants have succeeded in acquiring a foothold in the 

 southern and colder parts than elsewhere in New Zealand ; 

 and as we go farther north we find the number of acclimatized 

 species becoming more and more abundant. 'While those of Otago 

 are chiefly such as are to be met with in England and Scotland, 

 those of the north of Auckland are largely mixed with mid- 

 European plants, and many of tropical and sub-tropical distribution. 

 This is well seen by comparing the appearance at different ports. 

 On landing in the Bay of Islands, one sees large patches of 

 Agave Americana marking the sites of old gardens, but spreading 

 far and wide, as if quite at home. The ground is carpeted with the 

 familiar ' doab-grass,' as it is called in Bengal (Cynodon dactylon). 

 Lily-of-the-Nile (Richa7-dia) blocks the water-courses, while other 

 tropical forms {A?narantits, Aponogelon, Lyciiun, etc.) occur 

 freely as wild plants, intermingled with others of much more tem- 

 perate habitat. Pursuing his journeys south, the traveller enters 

 Napier, and, passing from the landing-place to the town through a 

 ravine-like cutting, finds scarlet geraniums and forests of fennel 

 competing with mesembryanthemum and introduced fuchsias for 

 possession of every bit of soil. He infers at once a climate quite 

 free from frost. But now let him land at Dunedin, and none 

 but old country friends meet him. Shepherd's purse, groundsel, 

 and docks occupy the wayside with similar equally familiar weeds. 

 The meadows and pastures are white with daisies and ox-eyes 

 (Chrysani/iei?iu7n leucanthemuni), or yellow with cat's-ear {Hypo- 

 cha'ris radicaia), buttercups, and self-heal {Prunella), and, with 

 a slight effort of imagination, he might almost fancy that he was 

 back in ' bonny Scotland.' The tropical element is here wanting. 

 While nearly four hundred (387) species Jiave been recorded as 

 occurring in the Auckland district, not more than 160 are known 

 from Otago in the south. 



It is a much-disputed question among local botanists, whether 

 the native flora can hold its own against the introduced plants, or 

 not. 'When we consider that species brought from old (from a 

 human point of view) and long populated countries, in more or less 

 close proximity to one another, have acquired their present charac- 

 teristics after long ages of a keen struggle for existence with one 

 another, and with herbivorous animals to fight against, we should 

 certainly expect them to prove extraordinarily aggressive in such a 



country as this. Here the animals are wanting, the climate is 

 milder, moisture is abundant, and all the field seems to lie open. 

 Accordingly, wherever the settler goes with the axe and plough, 

 and, above all, with fire, the introduced plant follows him, and 

 thrives. But it is now pretty well ascertained that if man stays his 

 hand, the native vegetation does not continue to recede before the 

 alien : on the contrary, it seems once more to tend to re-assert 

 itself. That, at least, is the testimony of our two most competent 

 botanists, Mr. Cheeseman in Auckland, and Mr. Kirk in Welling- 

 ton, as well as of the writer in Otago. 



The way that some plants have spread is most remarkable. The 

 common thistle {Cardiius lanceolatits) has gone over the country 

 like smoke, especially following fire and cultivation. When first 

 established, it forms thickets which frequently are impermeable ; 

 but this state never lasts long. The soil appears to refuse, at the 

 end of two or three years, to yield up its former abundance, and the 

 plant exhausts itself. This process in many parts is absolutely 

 beneficial to the soil. In the limestone districts to the north of 

 Otago, the writer has seen vast areas, which had been once 

 ploughed, covered with an impenetrable forest of thistles six feet or 

 more in height. In autumn the whole crop dies down, leaving the 

 rocky soil penetrated in all directions by its long roots. As these 

 decay, water finds its way down to the lower levels ; and on plough- 

 ing the soil, and sowing a crop of winter wheat, the farmer is re- 

 warded by a sixty-bushel crop. 



Two or three species truly indigenous are now abundantly repre- 

 sented by the introduced European form. This is certainly the 

 case with the AaxiAtWon {Taraxacmn) and sowthistle {Sojtchus), 

 and most probably also with the smooth geranium (G. molle). The 

 native form is all but extinct, the introduced being abundant. 



In some cases characters are developed which appear to tend 

 towards the formation of new varieties. Thus Bartsia viscosa, 

 always considered a root-parasite in Europe, is truly established on 

 its own roots in this country. Water-cress, which grows to a length 

 of from two to four feet in its native habitats, attains gigantic pro- 

 portions in many New Zealand streams. In the Avon at Christ- 

 church it is frequently found with stems as thick as a man's wrist, 

 and twenty feet in length. Sheep's-sorrel (Rumex acetosella) is 

 here an unmitigated garden and field pest, especially in poor soils, 

 where its tough underground stems will creep as much as a yard in 

 a season, if the soil be kept well stirred. Equally remarkable is the 

 changed character of Poa praiensis, so famed as a pasture-grass in 

 the States. In New Zealand it gives a poor return as a permanent 

 pasture-grass, while in arable land it is a curse, matting the surface 

 soil into an unworkable mass. No doubt one cause of the trouble- 

 some nature of many of the common garden-weeds is the compara- 

 tive absence of frost. Many plants which are strictly annuals in 

 Europe or America, become biennial or perennial here. Chickweeds 

 {Stellaria and Cerastitcni) and groundsel flower all the year round. 



One of the most aggressive species in the country is the white or 

 Dutch clover {Trifoliuin repens), which has shown great power of 

 spreading, both laterally and vertically. Introduced plants are often 

 met with also in most unexpected localities. The writer, when 

 rambling along the slopes of Mount Torlesse, in the Canterbury 

 Alps, was surprised to find some of the valleys — miles away from 

 human habitation — full of a common mullein ( Verbascum thap- 

 sus) ; but such instances are rare. The botanist rather wonders, 

 that, considering how greatly specialized to their surroundings New 

 Zealand plants are, they do not more quickly succumb to the in- 

 truders. 



Finally, an interesting question, puzzling to the acclimatizer, is the 

 difficulty of introducing certain — to him — desirable plants. Prim- 

 roses and cowslips, foxgloves, and many other sylvan and meadow 

 beauties, will not run wild. They die out if removed from the 

 garden. The cause seems to lie in the absence of the insects 

 necessary for their fertilization. 



Both in the case of plants and animals, then, an interesting field 

 for future observation exists in this country ; and fortunately, ac- 

 curate information on the whole subject has been accumulating 

 from the very outset, so that the future naturalist has no ' dark 

 ages ' to look back to, but will always have some trustworthy record 

 to refer to. Geo. M. Thomson. 



Dunedin, Aug, ii. 



