attacked by this larva, as are occasionally walnut (Juglans regia) and a species of Eucalyptus. The larva of Melanchra (Mamestra) mutans, Walk., frequently does very serious damage to the leaves of young wheat, and considerable portions of the crops have been destroyed at various times, particularly in the Canterbury district. M. composita, Guenée, known as the "grass-moth" or "grass-caterpillar," does great damage and causes heavy losses to bush farmers especially. Fortunately these animals are kept in check to a considerable extent by certain ichneumons as Probolus sollicitorius, Fabr., Mesostenus albopictus, Smith, as well as the introduced (?) Ryssa semipunctata.

Liothula (Eceticus) omnivora, Fereday, has occasionally done much damage among raspberry plantations.

The caterpillar of Ctenopseustes obliquana, Walk., which usually feeds on manuka and other native shrubs, has developed a fondness for the ripe fruit of plums and apricots.

The larvæ of Cacacia excessana, Walk., attacks the outsides of apples, and these have frequently been sent in to the Agricultural Department under the impression that they were attacked by the larvæ of the introduced codlin moth (Carpocapsa pomonella). The latter, however, attacks the core of the fruit, while that of Cacœcia only attacks the outside. This insect also attacks and disfigures the cherry-laurel (Prunus lauro-cerasus).

Two native species belonging to the Caradrinidæ may be mentioned in this connection. Agrotis ypsilon, Bott., is known in New Zealand as the tussock moth, the larvæ doing considerable damage in tussock country; it is also a very common pest in vegetable gardens. In Hawaii, where it is known as the greasy cutworm, it is very prevalent, and attacks cotton and tobacco.

Cyrphus unipunctatus, Hawthorne, which is very abundant in the North Island, occasionally attacks grain crops, but is apparently kept in check to a considerable extent by birds. In North America it is one of the most serious of the cereal crop pests.

Among Coleoptera only a few instances are recorded.

Emona humilis, Newman, attacks lemon trees in the northern orchards, and eats into the wood.

Xyloteles griseus, Westwood, has been reported several times as attacking fig trees, while X. lætus, White, sometimes called the "appleborer," occasionally destroys the apples on the trees.

All three species of beetles belong to the Cerambycidæ, one of the few families reported to contain destructive pests, but none of them have become serious.

The larva of Odontria striata, White, commonly known as the "grass-grub," is a very destructive insect, especially in pastures and

lawns. It cuts the grass at the roots, and in this manner destroys the plants, so that the surface growth dies right out. The larvæ are sufficiently deep in the soil to be beyond the range of starlings and other insectivorous birds, and the chief means of destruction are either flooding the land, or rolling with a very heavy roller.

Two indigenous scale insects have been recorded as attacking introduced plants. In the Agricultural Department's Report for 1909, Diaspis santali, Maskell, is reported as becoming troublesome in orchards, where it attacks the plum trees; while Dactylopius aurilanatus, Maskell, has established itself on Norfolk Island Pines and other species of Araucaria in the North Island.

Though these few are the only examples recorded of indigenous species of insects attacking introduced plants, it must be noted that the small number is probably due to the fact that observations on the point have not been made. Anyone taking up a research on this subject would find that the list might be multiplied to a very great

extent.

Inter-relation of Native and Introduced Flora

The introduction of foreign plants into New Zealand has wrought a very radical change in the facies of the vegetation. The distinctive character of the native flora has disappeared from nearly all closely settled portions of the country, and what may be called a cosmopolitan type of vegetation has taken the room formerly occupied by the displaced species. This fact led many naturalists to the conclusion that the indigenous fauna was doomed to destruction, and would in time be exterminated by the alien introductions. Sir J. D. Hooker, who visited New Zealand in 1841, and published an account of its plant life in the Flora Nova-Zealandia, which forms the second part of the Botany of the Antarctic Expedition of Sir J. Ross, published in 1854-5, was the first who voiced this conclusion, and the pre-eminent position he occupied as the leading British botanist, deservedly and naturally caused his views to be widely accepted. He came to the conclusion that the northern or Arctic element in all the south temperate floras, including that of New Zealand, was due to the wonderful aggressive and colonising power of what he termed “the Scandinavian Flora." He says:

When I take a comprehensive view of the vegetation of the Old World, I am struck with the appearance it presents of there being a continuous current of vegetation (if I may so fancifully express myself) from Scandinavia to Tasmania.... Scandinavian genera, and even species, reappear everywhere from Lapland and Iceland to the tops of the Tasmanian Alps in rapidly diminishing numbers it is true, but in vigorous development

throughout;...and in New Zealand and the Antarctic Islands, many of the species remaining unchanged throughout.

Darwin in the Origin of Species states that:

from the extraordinary manner in which European productions have recently spread over New Zealand, and have seized on places which must have been previously occupied, we may believe, if all the animals and plants of Great Britain were set free in New Zealand, that in the course of time a multitude of British forms would become thoroughly naturalised there, and would exterminate many of the natives. On the other hand, from what we see now occurring in New Zealand, and from hardly a single inhabitant of the southern hemisphere having become wild in any part of Europe, we may doubt, if all the productions of New Zealand were set free in Great Britain, whether any considerable number would be enabled to seize on places now occupied by our native plants and animals.

Arguing from the facts advanced by Sir J. D. Hooker, A. R. Wallace in Island Life (1880) has discussed the question at some length, and I quote that portion of his remarks which bears directly on the New Zealand flora. He says (p. 479):

The first important fact bearing upon this question is the wonderful aggressive and colonising power of the Scandinavian flora, as shown by the way in which it established itself in any temperate country to which it may gain access. About 150 species have thus established themselves in New Zealand, often taking possession of large tracts of country; about the same number are found in Australia, and nearly as many in the Atlantic states of America, where they form the commonest weeds. Whether or not we accept Mr Darwin's explanation of this power as due to development in the most extensive land area of the globe where competition has been most severe and long-continued, the fact of the existence of this power remains, and we can see how important an agent it must be in the formation of the floras of any lands to which these aggressive plants have been able to gain access.

Wallace was very strongly impressed by several instances of the rapid spread of European plants in New Zealand which had been communicated to him by Enys, Travers, and other good observers. Some of the examples given by Wallace in Darwinism may be referred to here. Thus he gives instances of the spread of water-cress in the streams of the Canterbury Plains; of white clover displacing native species and even exterminating the native flax (Phormium tenax); of Hypocharis radicata (the so-called Cape-weed of the South Island): which destroyed excellent pasture in three years, and absolutely displaced every other plant on the ground. It grows on every kind of soil, and is even said to drive out the white clover, which is usually so powerful in taking possession of the soil;

of knot-grass (Polygonum aviculare), common dock (Rumex obtusifolius), sowthistle (Sonchus oleraceus) and sorrel (Rumex acetosella),

spreading in all directions, and in many places absolutely occupying the ground they invaded.

Many of these statements are unintentionally misleading. Thus Hypocharis radicata, the most abundant and most widespread introduced plant into New Zealand, can only assert itself in land grazed over by cattle (it asserts itself in lawns), which eat out all the good grasses and the clover, and leave the others. When sheep are introduced the Cape-weed is itself quickly eaten out. Dr Cockayne is very emphatic on the subject. He says:

The often quoted stories of white clover being able to wipe out Phormium tenax, of Salix Babylonica overcoming the water-cress, of Hypocharis radicata displacing every other plant of excellent pastures in Nelson, are without foundation. P. tenax has certainly been eradicated in many places, and perhaps, in a sense, replaced by white clover, but not until fire and feeding of stock had killed the plant.

Dr Cockayne's reference is to a well-known passage in Darwinism: A curious example of the struggle between plants has been communicated to me by Mr John Enys, a resident of New Zealand. The English water-cress grows so luxuriantly in that country as to completely choke up the rivers, sometimes leading to disastrous floods, and necessitating great outlay to keep the streams open. But a natural remedy has now been found by planting willows on the banks. The roots of these trees penetrate the bed of the stream in every direction, and the water-cress, unable to obtain the requisite amount of nourishment, gradually disappears. Enys is partly right in this statement. I have recently noticed that a species of Nitella, whether native or introduced I do not know, is killing out the water-cress in some of the streams about Christchurch.

W. T. L. Travers, addressing the Wellington Philosophical Society in 1871, in referring to the destruction of the native alpine and subalpine flora of Nelson province said:

Indeed I have no doubt, from the comparative rarity of many plants which were formerly found in abundance in such districts, that in a few years our only knowledge of them will be derived from the dried specimens in our herbaria.

In another place, quoted by Cheeseman, he stated:

Such, in effect, is the activity with which the introduced plants are doing their work, that I believe if every human being were at once removed from the islands for even a limited number of years, looking at the matter from a geological point of view, the introduced would succeed in displacing the indigenous fauna and flora.

I have no doubt that had Travers been living to-day he would have completely reversed this judgment. The opinion of all botanists in New Zealand to-day is that when the direct, or—to a large extent—

the indirect influence of man is eliminated, the native vegetation can always hold its own against the introduced. Those plants which have thriven abnormally in this new country, and have impressed visitors by their abundance, are found in settled and cultivated districts, and belong chiefly to what are known as weeds of cultivation, that is, plants which have become adapted to conditions caused by the direct and indirect action of human beings, and which only thrive where those conditions are maintained.

In a paper on plant acclimatisation in New Zealand which was published in 1900 I said:

Seeds of such plants as violets, primroses, cowslips, bluebells, heaths, etc., and of fruits like the bilberry (or blæberry) and cranberry, have been sown by numbers of persons during the past 50 or 60 years in all sorts of situations, but they have not established themselves. They cannot always succeed even when growing in open competition against the indigenous vegetation, and they never make the slightest headway against many of the vigorous introduced forms. Even where individual plants become established, they nearly always fail to produce seed, and this is the chief reason why such species do not become naturalised. In their native countries their flowers are visited and fertilised by certain species of insects, and these are totally wanting here. Our indigenous insects are unable to fertilise them, and so they do not produce seed. There are no doubt other differences which affect their success in the struggle for existence. The rapidity of germination of their seeds, the subsequent rapidity of growth of the young plants, and many other factors, which have not been sufficiently looked into in this connection, all bear on this question. I have in past years sown quantities of the seeds of many flowering plants of Great Britain along the wayside in one of the suburban roads leading through our Town Belt, but from none of them have plants appeared except from those of foxgloves, whose strong coarse foliage enables it to hold its own against most of its neighbours. If the others have germinated they have nearly always been smothered by cocksfoot or other coarse grass. In gardens many of our European flowers seed now on account of the general prevalence of humble-bees, but many others remain unfertilised.

Most of the common naturalised plants are capable of self-fertilisation if they are not habitually self-fertilised. For instance the following are found producing seeds in midwinter from flowers which never open and which are more or less imperfect in structure: Shepherd's Purse (Capsella Bursa-pastoris), winter-cress (Barbarea vulgaris), bitter-cress (Cardamine hirsuta), hedge-mustard (Sisymbrium officinale), wart-cress (Senebiera didyma), chickweed (Stellaria media), mouse-ear chickweed (Cerastium glomeratum and C. triviale), groundsel (Senecio vulgaris), sowthistle (Sonchus oleraceus), spurge (Euphorbia Peplus), and perhaps others. This faculty of producing more or less imperfect self-fertilised flowers is almost an essential feature in all such plants, many of which are thus enabled to produce fruit at all seasons of the year, and almost independent of the weather. Another point is that most of them produce very small and