[Read before the Otago Institute, 31st January, 1881.]
Among the many questions of interest which offer themselves for solution to the botanist, none possess more fascination than those dealing with the geographical distribution of plants; and if this is so in other parts of the world it is doubly so in New Zealand, where the existing conditions are almost unique. The present distribution of our flora leads up to a wider and far more interesting question, viz., its origin, and the investigation of this brings under review many collateral subjects, among which may be considered the former land connections existing between what is now New Zealand and other parts of the world.
The main question cannot be considered alone, but must be taken in conjunction with the origin and distribution of our fauna, and with the great geological changes which have been effected in past times, and which have brought about in our time a distribution of land and water very different from that which existed at the end of the Secondary or commencement of the Tertiary period.
But it would be almost impossible in the limits of a single address to discuss the subject in all its aspects, and I shall therefore confine myself to a small portion only of it, stating in the first place what has been written on this topic, and then pointing out some of the interesting facts which an examination of it reveals.
Every naturalist who has visited New Zealand has had his attention drawn to the many remarkable features of its fauna and flora, but Sir Joseph Hooker, Professor F. W. Hutton, and Mr. Wallace, are the only writers whose works I am acquainted with, who have attempted to solve the problems presented to them.
The first-named botanist in the introduction to the “Flora Novæ-Zealandiæ” has summarized the information at his disposal in a masterly essay, which forms the basis of our knowledge as to the distribution of the Flora. But he has not sought to trace the origin of our species more directly, confining himself to their affinities and to their occurrence in other countries, but not seeking to solve the question as to how they have found their way here. Between the publication of the “Flora Novæ-Zealandiæ” (in 1853) and the issue of the “Handbook” (in 1867), about 200 species of flowering plants were added to the Flora, while up to date about 150 more species have been added, bringing the total up to 1,085 species. More close and accurate investigations of many of our local botanists are
the means of continually adding to this list. Still the general conclusions arrived at in the “Flora Novæ-Zealandiæ” have not been materially altered by recent discoveries.
Sir Joseph Hooker was struck by the preponderance of Australian types among those plants which he found to be common both to New Zealand and other countries of the world. Nearly one-fourth of these plants were Australian, nearly one-eighth South American, and one-tenth common to both Australia and South America. Of the remainder about one-twelfth were shown to be European and one-sixteenth antarctic. When we find similar plants in two widely-separated parts of the globe, we are naturally led to consider how they have reached these distant localities, and if no satisfactory solution of the question is afforded by an examination of their structural means of dispersion, we are further tempted to speculate on the former land connections which have existed. The preponderance of Australian plants in New Zealand is not to be accounted for by proximity alone, as the wide extent of sea which separates the countries forms the most effectual of all barriers to the migration of the majority of plants. Sir J. Hooker points out that no theory of transport of the forms common to the two regions will account for the absence of “the Eucalypti and other Myrtaceæ, of the whole immense genus of Acacia, and of its numerous Australian congeners,” or the absence of Casuarina, Callitris, Dilleniaceæ, etc., and the variety of such large Australian orders as Proteaceæ, Rutaceæ, and Stylidieæ. Nor will any theory of variation account for these facts. And he continues: “Considering that Eucalypti (Myrtaceæ) form the most prevalent forest feature over the greater part of South and East Australia, rivalled by the Leguminosæ alone, and that both these Orders (the latter especially) are admirably adapted constitutionally for transport, and that the species are not particularly local or scarce, and grow well wherever sown, the fact of their absence from New Zealand cannot be too strongly pressed on the attention of the botanical geographer, for it is the main cause of the difference between the floras of these two great masses of land being much greater than that between any two equally large contiguous ones on the face of the globe.” Read in the light of our accumulated knowledge, the following remark is of interest: “New Zealand, however, does not appear wholly as a satellite of Australia in all the genera common to both, for of several there are but few species in Australia, which hence shares the peculiarities of New Zealand rather than New Zealand those of Australia.” That is to say, that he saw that those plants which occur both in Australia and New Zealand had not necessarily all passed from the former to the latter country, but that in many cases the opposite had occurred. After describing the affinities existing between the plants of New
Zealand and those of South America, Europe, and the antarctic regions respectively, and further pointing out some remarkable Pacific Island peculiarities in our flora, Hooker concludes by stating that the existing botanical relationships “cannot be accounted for by any theory of transport or variation,” but that they are “agreeable to the hypothesis of all being members of a once more extensive flora which has been broken up by geological and climatic causes.”
Leaving out of account minor speculations on this subject, we may next consider the second writer named, who deals—although indirectly—with the question.
Prof. Hutton's theory*, deduced from the distribution of the struthious birds in the southern hemisphere, is that there formerly existed a great “antarctic continent stretching from Australia through New Zealand to South America, and perhaps on to South Africa. This continent must have sunk, and Australia, New Zealand, South America, and South Africa, must have remained isolated from one another long enough to allow of the great differences observable between the birds of each country being brought about. Subsequently New Zealand must have formed part of a smaller continent, not connected either with Australia or South America, over which the moa roamed. This must have been followed by a long insular period, ending in another continent still disconnected from Australia and South America, which continent again sank, and New Zealand assumed somewhat of its present form.”
It is of course assumed that this former extensive antarctic continent existed at a date anterior to the first occurrence of mammals either in Australia or South America, and consequently that all subsequent immigrants from Australia, or from the islands lying to the north, must have found their way across the intervening expanses of ocean. Professor Hutton recognizes many of the difficulties in the way of this theory, as, for example, the occurrence of grass-birds (Sphenæacus) in both Australia and New Zealand, and the existence of the genus Ocydromus (woodhens, etc.) in New Zealand, Lord Howe's Island, and New Caledonia; as the birds of both these genera are almost or quite unable to fly.
The examination of our fresh-water fish leads him to the conclusions “either that our connection with Australia was later than with South America, or that in the old continent New Zealand and Australia were inhabited by one, and South America by another species” of the grayling family. “The fresh-water fish also prove that our connection with the
[Footnote] * On the Geographical Relations of the N.Z. Fauna, by Captain F. W. Hutton. “Trans. N.Z. Inst.,” vol. v., p. 227.
Chatham and Auckland Islands was much later than with Australia.” And then he goes on to say:—“The distribution of Anguilla latirostris, which is not found nearer than China (and of A. obscura, a closely allied species, which occurs in the Fiji Islands), adds its testimony to that of Lotella and Ditrema (other species named by him), of a former connection with that part of the world, not by way of Australia; and we shall find that this remarkable connection with China and the Indian Archipelago, thus dimly shadowed out by the fishes, gets stronger and stronger as we review the invertebrate animals.”
The examination of these lower forms leads to the same general conclusions—a strong relationship on one hand with Australia, and a similar, but distinct, relationship with islands and countries to the north.
In summarizing the facts of the geographical distribution of the fauna, the following results are arrived at by him:—1. “A continental period during which South America, New Zealand, Australia, and South Africa were all connected, although it is not necessary that all should have been connected at the same time, but New Zealand must have been isolated from all before the spread of mammals, and from that time to the present it has never been completely submerged. This continent was inhabited by struthious birds,” etc., etc.
2. After a period of subsidence, a second continent came into existence, “stretching from New Zealand to Lord Howe's Island and New Caledonia, and extending for an unknown distance into Polynesia, but certainly not so far as the Sandwich Islands.” And while this continent was connected with China either directly or by a chain of islands, it must have been cut off from the New Hebrides by a strait.
3. “Subsidence again followed, and New Zealand was reduced for a long time to a number of islands, upon many of which the moa lived.” This supposition is necessary to account for the number of species of Dinornis which formerly existed, as the birds must have been “isolated from one another for a sufficiently long period to allow of specific changes being brought about.”
4. Elevation ensued, the isolated islands became connected together into one large island, which was not however connected with Polynesia, and over which the various species of moa roamed. And lastly,
5. By a process of subsidence the islands assumed something of their present form.
This theory is a most ingenious one, and is well worked out, and had available information been at hand as to the depth of the circumjacent seas, no doubt many of the conclusions arrived at would have been modified. The geological evidences are adduced in support of it, and though the dis-
tribution of the flora is not critically gone into, certain remarkable facts of the distribution of genera such as Eucalyptus, Stilbocarpa, Metrosideros and others, are brought forward by way of corroboration.
Some four years after the publication of Professor Hutton's paper, Mr. A. R. Wallace's great work on the “Geographical Distribution of Animals” came out, in which due consideration is given to the question of the origin of the New Zealand fauna, and to the discussion of Professor Hutton's views. Mr. Wallace in this work does not agree with the idea that there was a former great antarctic land connection, but believes that there was a great southward extension of land, perhaps considerably beyond the Macquaries, and that this being within the range of floating ice during the colder epochs, and within easy reach of the antarctic continent during the warm periods, there arose “that interchange of genera and species with South America, which forms one of the characteristic features of the natural history of New Zealand.” Professor Hutton's theory is primarily based on the distribution of the struthious birds, but Mr. Wallace is of opinion that the ancestral struthious type probably once spread over the larger portion of the globe, and that as higher forms, particularly of the Carnivora, became developed, it was exterminated everywhere except in those regions where it was free from their attacks, and that in these regions it developed into special forms adapted to surrounding conditions. This conclusion is supported and rendered almost certain by the discovery of remains of this order in Europe in eocene deposits, and by the occurrence of an ostrich among the fossils of the Siwalik Hills.
While considering that no other form of animal inhabiting New Zealand requires a land connection with distant countries to account for its presence, Mr. Wallace concludes, in accordance with principles well established in an earlier part of his work, that the existence is demonstrated of an extensive tract of land in the vicinity of Australia, Polynesia, and the Antarctic Continent, without having been actually connected with any of these countries, since the period when mammalia had peopled all the great continents.
Last year the issue of Mr. Wallace's most interesting work on “Island Life,” added another contribution to our knowledge of the question under discussion, and the three chapters devoted to New Zealand put the problems very clearly before us. A very important factor, and one which had not hitherto been considered, is now introduced—viz., the relative depths of the seas surrounding Australia and New Zealand. It is shown, by the aid of a map, that if the whole of the circumjacent ocean, which is at present less than 1,000 fathoms in depth, was to be elevated above sea-level, a very
remarkable change in the conformation of the existing land would take place. New Zealand would be extended very greatly to the west and northwest, and two long narrow arms would stretch, one to Lord Howe's Island, and the other by Norfolk Island to the Great Barrier Reef, and thus a connection with North-eastern Australia would be made. The same elevation would extend the area of Australia round its western, southern, and eastern coasts, while a long tongue of land would unite it with Tasmania, and would reach to the 50th parallel S. latitude. But even with this great elevation of 6,000 feet, a wide sea would remain between New Zealand and temperate Australia. The northern extension of Australia would connect it on the one hand with Malaysia, Borneo, and Celebes, while from New Guinea a broad eastern extension would include the New Hebrides. Starting from these indications Mr. Wallace shows that we ought to expect to find that New Zealand was most probably connected at a remote period “with tropical Australia and New Guinea, and, perhaps, at a still more remote epoch, with the great southern continent by means of intervening lands and islands,” as “a submarine plateau at a depth somewhere between one and two thousand fathoms stretches southward to the antarctic continent.”
It is not my intention here to follow Mr. Wallace in all the arguments he adduces to show the origin of our fauna, but a few of his facts are suggestive and confirmatory of his theory, as opposed to that of Professor Hutton, which he again discusses at some length. Thus our struthious birds are shown to be allied, not to the rheas of South America, but to the cassowaries and emus of North Australia and New Guinea. Again, “the starling family, to which four of the most remarkable New Zealand birds belong (the genera Creadion, Heteralocha, and Calleas), is totally wanting in temperate Australia, and is comparatively scarce in the entire Australian region, but is abundant in the Oriental region, with which New Guinea and the Moluccas are in easy communication. It is certainly a most suggestive fact that there are more than sixty genera of birds peculiar to the Australian continent (with Tasmania), many of them almost or quite confined to its temperate portions, and that no single one of these should be represented in temperate New Zealand.”
But this connection with tropical Australia must necessarily have been at a remote period, before the latter received its mammalian fauna, or else that portion of Australia which was in connection with New Zealand “was itself isolated from the mainland, and was thus without a mammalian population.” And this is the essentially novel and interesting part of the theory which Mr. Wallace seeks to prove by an examination of our flora, and by the existing geological conditions of Australia.
Stated concisely, his conclusions are that for a long period of time Australia was divided into two islands, a western and an eastern. In the former of these, the peculiarly characteristic Australian genera, both of plants and animals, originated. The eastern island stretched in a long narrow line from the tropics to the south of Tasmania, and in connection with its tropical portion there was probably a prolongation of New Zealand to the north-west. By this bridge, with its southerly and south-easterly ramifications, a stream of immigrants set in from the tropical regions further north, so that numerous genera and even species of plants, as well as some animals, were spread along both shores of the sea separating New Zealand from Australia. The subsequent depression of the northern area caused a separation of New Zealand from tropical Australia, while the elevation of the comparatively shallow sea separating the western from the eastern island, united these two into the great continental island of Australia, over the whole of which the peculiar western forms spread rapidly, and apparently at a much greater rate than the tropical and eastern species did. While the presence of the Australian, Asiatic, and Polynesian elements in the New Zealand flora are traceable to this former land connection, the antarctic and South American forms are believed to be due to immigration from outlying islands and extensions of land to the south, and the European, or more correctly the arctic element, is explained by the extraordinarily aggressive character of the so-called Scandinavian flora, which has enabled it to push its colonists over the three great southern areas, viz., South Africa, South America and Australasia.
Mr. Wallace's explanations of the origin of our flora must commend themselves as extremely satisfactory to every one capable of judging of the questions under consideration. Our subsequent knowledge may modify some of his conclusions to a slight extent, but it is by the publication of such hypotheses and theories, and the application of them for the solution of difficult problems, that correct ideas are most rapidly attained. Not only is our interest heightened by such speculations, but definite issues are placed before our minds, and we are enabled to judge more and more accurately of these, and to recognize how vast the field to be traversed is. It is well to bear in mind that as our stock of facts increases, so also does our knowledge of our ignorance, and that the latter often increases in a much more rapid ratio than the former. We begin by discussing a limited question, satisfied perhaps that we have sufficient information accumulated to enable us to give a definite answer, but at every turn collateral points are raised, until at last we feel ourselves face to face with an overpowering mass of questions all demanding solution, and are at the same time conscious of our inability to grapple with them. But it is only given to the few—to a
very limited few indeed—to be able to generalize and build up into a homogeneous whole the heterogeneous materials collected by the multitude. We can all help to accumulate these materials together, leaving it to the master-minds of science to use the fruits of our labour.
I have very briefly attempted to show what are the principal theories enunciated to account for our flora. I now propose to examine some of the modes by which plants become distributed, particularly noticing their application to New Zealand plants, and further, to show a little more in detail than Mr. Wallace could afford to do in a general work, the relations of our flora to that of Australia.
In examining such a problem as the distribution of plants, it is manifest that one of the most important considerations to be taken into account is their mode of dispersal, and chiefly, of course, the mode of dispersal of their seeds. Some plants, such as the strawberry, no doubt have the power of spreading themselves over wide areas by means of their long trailing shoots, as we see this plant doing at the present day wherever it has been introduced. But even the strawberry appears to be dispersed much more by its seeds than its suckers, and it is the seed therefore which must be considered chiefly. The most important agents concerned in the dispersal of seeds are (1) the wind; (2) birds or other animals; and (3) ocean currents. Besides these, icebergs may have been the means of bringing some plants to our shores; rivers have certainly distributed them from higher to lower levels; and lastly, human agency has been an efficient cause in late years. But for the first of these extra causes—viz., icebergs—we have no data beyond very general ones to go upon, and the other two have little bearing on the wide question of the origin of the flora.
The wind is certainly a most efficient agent in the dispersal of seeds, and many plants have their seeds specially adapted for the purpose of being so distributed. The order Compositæ shows the greatest specialization in this respect, the calyx-limb being modified in a large proportion of the species into a pappus, which acts as a parachute. The order is the largest in the New Zealand flora, numbering 24 genera and including 167 species, but from its wide-spread means of dispersion is of less value than less highly differentiated orders. The majority of our plants of this order are either Australian or are allied to Australian forms, a few being of very wide distribution. Another contrivance for wind-dispersion is found in the persistence of the stigma in the form of long feathery awns on the achenes. This is represented in the genus Clematis, a genus occurring in all temperate climates, and of which the New Zealand species, as well as the Australian, are all endemic. Its origin here is therefore an open question. The genus Atherosperma, belonging
to a specially South American order, is similarly characterized, but its occurrence here has no special significance, as Australia possesses an endemic species as well as New Zealand. The genera Epilobium and Parsonsia both have tufts of hair on their seeds to aid in their dispersal; the former is a very wide-spread genus in all temperate regions, and some of its species are common to both hemispheres; while the latter is an Asiatic and Australian genus. The only other contrivances which aid in the wind-dispersal of our New Zealand plants are wings on the fruits or seeds. These occur, but feebly developed, on the nuts of Fagus, and on the seeds of Knightia, Dammara, and Libocedrus. The first of these occurs in both the north and south temperate regions; but our and the Australian species are all probably of antarctic origin. The second genus has one New Caledonian representative, and the third is Australian, Malaysian, and Polynesian in its distribution, while Libocedrus is found only in New Zealand and South America.
While special adaptations for wind-distribution are apparently few in New Zealand plants (if we except the Compositæ), there are no doubt many seeds which are readily blown about by reason of their small size and lightness. I have no data to guide me here, but will instance the order Orchideæ, all the species of which have minute, light seeds, and all the genera of which are either Australian or from further north, or have an Australian facies.
The second mode of dispersal mentioned is by means of birds, and this is accomplished in three ways—“either by swallowing fruits and rejecting the seeds in a state fit for germination, or by the seeds becoming attached to the plumage of ground-nesting birds, or to the feet of aquatic birds embedded in small quantities of mud or earth.” With regard to the first of these modes, it is probable that the bright colours of most succulent fruits serve to render them conspicuous and attractive to birds, which are thus led to swallow them. But most seeds, enclosed in fleshy pulp, are furnished with a hard shell or test, and most fruit-eating birds have a very soft gizzard, incapable of grinding-up the food which they eat, and so it happens that these birds become the unconscious means of distributing plants producing such succulent fruits. I find that altogether some 59 genera of plants in New Zealand produce succulent fruits, mostly drupaceous, that is, having the inner layer of the pericarp hard or stony, so as to protect the seeds. And of these no less than 41 genera are common to these islands and Australia or the tropics of the Old World. Only 18 of these genera occur also in America, and their range is either very wide, as in the case of Myrtus, Eugenia, Solanum, Cassytha, and Astelia, or they are of antarctic distribution, and have in most cases invaded
Australia and countries to the north as well as New Zealand. Coriaria, Fuchsia, and Callixene are the only New Zealand genera with succulent fruits which occur in South America, but not in Australia, or any other land to the north of New Zealand. When it is remembered that most of our land birds are either characteristic of the Australian region or are allied to Australian forms, a certain amount of light is thrown upon this subject. It must not, however, be supposed that the possession or the want of succulent fruit is a character of great importance or significance; it is probably a very minor character, as even in the same species (e.g., Gaultheria antipoda) we may find great differences in the extent to which succulent tissue is developed in the pericarp of the fruit. Still it constitutes one of those minor coincidences, the sum of which, when taken together, throws considerable light on this and kindred questions.
Besides swallowing the fruits of plants and rejecting the seeds, birds carry seeds attached to their plumage. A few grasses may be thus carried by means of their hispid awns, and the seeds of some Pittosporums may adhere by their glutinous surface, but with these exceptions I only know of two genera which owe their means of dispersal to any special contrivance which enables their seeds to adhere to passing objects; these are Acæna and Uncinia. In the former genus, the four angles of the persistent calyx are produced into spines, which in the majority of the species bear small barbs at their apex, and the fruit thus adheres very readily; the genus is confined to the southern hemisphere, except in America, where it has spread as far as Mexico and California, and in Polynesia as far as the Sandwich Islands. The occurrence of the barb is a very peculiar feature in the New Zealand species. The common piripiri (A. sanguisorbæ) is a native of Australia, Tasmania, and Tristan d'Acunha, as well as New Zealand, and the calyx-spines are always barbed. A. adscendens, another barbed species, occurs also in Fuegia and the Falkland Islands, while A. novæ-zealandiæ, a third barbed species, though endemic, is altogether too near A. sanguisorbæ to rank as an exception. The other four species are also endemic, and of these A. depressa bears barbs, while the other three, A. microphylla, buchanani, and inermis, are almost entirely without them. The barbs, while no doubt of use in adhering to the feathers of birds, are best fitted to stick to the hair and skin of passing animals, and I think that in these smooth-spined Acænas we have a case of loss of an organ through disuse.
The other specially furnished genus is Uncinia, sedges which occur chiefly in the southern hemisphere, but range as far north as the mountains of Abyssinia. The seed in every species is furnished with a long hooked bristle which springs from the base of the nut, and projects out of the utricle or sac enclosing the fruit. Our species are mostly endemic, but one
is almost identical with a Fuegian species, and one or two with Tasmanian forms. It appears to me probable that the singular Chatham Island Lily (or Forget-me-not), Myosotidium nobile, is derived from an originally barbed plant, and that by long isolation it has lost the barbed bristles on the nuts characteristic of the Australian genus Cynoglossum, its nearest allies, just as it has lost the hispid character considered so distinctive of other Boragineæ.
The last mode specified in which birds carry seeds, is—attached to the mud or earth which clings to their feet. This subject has already been so carefully and conclusively worked out, particularly by Mr. Darwin in the “Origin of Species,” that I need not do more than refer to it. Sir J. D. Hooker, in the recently-published (1879) account of the botany of Kerguelen Island (Challenger Expedition Reports), considers that the few species of flowering plants of that island, presenting, as they do, a decided Fugian facies, have been thus brought by land birds. These are very abundant on the Falkland Islands, where the vegetation is identical with that of colder South America, and favoured by the prevalent westerly gales and the numerous stepping-stones, probably in the form of islands formerly existing, these land birds have probably found their way to Kerguelen Island. And he goes on to say that “the absence of such birds from the present avi-fauna of the island offers no obstacle to such a speculation, as such immigrants would on arrival speedily be destroyed by the predatory gulls and petrels of the island.” It is probable that some of the antarctic and South American forms occurring in New Zealand, and also in Tasmania and South-east Australia, have been thus introduced; and this probability is increased if we assume, with Mr. Wallace, that changes similar to those which have occurred in the arctic regions have also taken place in the antarctic, viz., that great alternations of climate have occurred in past ages, during some of which the now ice-clad antarctic continent bore an abundant flora of south-temperate forms, obtained probably from South America, the nearest continental area.
The third mode of plant-dispersion alluded to is by means of ocean currents. This subject has also been carefully examined by Mr. Darwin, and the results of his interesting experiments are detailed in the “Origin of Species,” and have been largely employed by Wallace in accounting for the flora of oceanic islands, such as the Azores. I need not recapitulate these results here, but will merely point out that the length of time during which many seeds will float and retain their vitality, and also the probabilities of such seeds being carried to localities suitable for their germination, are probably much greater than the popular idea would assign to them. In former epochs, when there was a greater land extension, and, perhaps, a more tem-
perate climate in the antarctic regions, this mode of distribution may have sufficed to introduce some species into New Zealand, but it appears somewhat improbable that it still continues to any considerable extent. A correct knowledge of the oceanic currents which impinge on our coasts, will alone enable us to form an estimate of this means of plant immigration, and this information I do not possess.
Having considered very briefly these modes of plant dispersal, and noticed the geographical distribution and relationships of those genera which have been affected chiefly by their modifications of form, I would take a brief glance at the endemic forms which occur so abundantly in our islands. As these have probably all originated in or near the localities where they now exist, they can only aid us in the solution of the present question by their affinities. Many of these affinities are very difficult to establish, but in the majority of cases where the relationship of our endemic species to the flora of other countries is evident, it is found that Australian forms greatly predominate. Long isolation, together with complete change in their environment, has probably served to modify many of the immigrants, so that their affinities have become obscured, and this has acted in many cases so effectually as to mask them altogether. Usually variation first appears in the habit of the plant, and we see this in the form of the foliage, etc., of Ranunculus lyallii, our coriaceous Veronicas, Olearias, Ligusticums, etc. The same change is seen in recently-introduced plants, as in the common watercress (Nasturtium officinale), which in New Zealand rivers shows a tendency to assume a very different habit from its European parent. Protection against some forms of insect enemies, probably Orthop-terous, appears also to have played an effectual part in modifying the epidermal structures of many of our species, and may partly account for the prevalence of coriaceous-leaved and woolly plants, among the alpine species in particular. But we have little data here to go upon; and before passing on to the last part of this address I will just point out a few peculiarities of structure in our plants, which are of interest and full of suggestiveness.
One of these is the scarcity of spiny or prickly plants. As the function of spines and prickles is probably that of defence against mammalian enemies, we can readily understand the paucity of such contrivances in our plants. Even the apparent exceptions go to prove the rule in nearly every case. Where such defensive modifications do occur, we notice that the plants are usually to be found outside of New Zealand, and are most probably of foreign origin, their weapons of defence having been developed in countries where they were of service, and the New Zealand immigrants not having had sufficient time to lose them. Thus Discaria toumatou has its
branches and branchlets reduced to spines; but the genus is wide-spread in the southern hemisphere, and our species is almost identical with an Australian one. So strong a case cannot be made out with regard to Aciphylla, or spear-grass, whose leaves and bracts are all spinous, and constitute a most powerful means of defence. The genus is certainly found in Australia, but the spines are not developed to any extent in the Australian species, while our bayonet-leaved species are endemic. Hymenanthera, with excessively rigid branches, and Eryngium, with spinous leaves and bracts, are both genera which range into Australia, in the latter case the species being identical. The same remark applies to many of our harsh cutting-grasses or sedges, belonging to the genera Cladium, Gahnia, Lepidosperma, Carex, etc., all being genera having wide distribution outside of New Zealand, and some having identical species in Australia. Again we have apparent anomalies in Dracophyllum, with its pungent-tipped leaves (a character common, however, to the Australian species), and in Desmoschænus, the common, large, scabrid sedge of our sand-hills. Very few species have the fruit protected against grazing animals. The only cases I know of are Sicyos angulatus, of which the nut is covered with barbed spines, but which is a species common to Australia and parts of America; and Entelea arborescens, with a spinous capsule. This last plant is probably descended, after much modification, from a stray immigrant of a remote period, its nearest ally being Sparmannia, a Cape of Good Hope genus.
Even the following facts, slight and almost unappreciable as they are, tend to show that the absenee of grazing animals tends to modify species to a considerable extent. We have in New Zealand two species of manuka (Leptospermum); of these, L. scoparium, with pungent tips to its leaves, also occurs in Australia; L. ericoides, which wants the prickly tip, is endemic. Similarly there are two species of Leucopogon, of which L. frazeri, with a short spine or mucro at the apex of the leaf, occurs in Australia, and L. fasciculatus, with smooth leaves, is endemic. Lastly there are five heaths of the genus Archeria; of these, two occur in New Zealand and one in Tasmania, all having obtuse leaves; the other two occur in Australia, and have very acute almost spinous leaves.
The next matter bearing on this subject to which I now request your attention is the relation of our flora to that of Australia, as pointed out by Mr. Wallace in his latest theory, which is, that New Zealand was at one time connected with the Asiatic region by way of tropical Australia, while the whole of eastern Australia was an island separate from what is now Western Australia by a comparatively shallow sea. This, he affirms, is proven by the depth of the now intervening seas, by the geological forma-
tions of all the countries concerned, by the occurrence of so many New Zealand genera and species in Eastern Australia, and the absence from New Zealand of so many characteristic Australian orders and genera. It would be out of place here to go into these points minutely, because to do so would involve a mere recapitulation of Mr. Wallace's able and conclusive arguments, and I shall therefore confine myself only to a short examination of the relations of our flora to that of Eastern and Western Australia respectively. I have to apologize if I now descend into statistics, as the subject can hardly be treated in any other manner.
New Zealand possesses altogether 310 genera of flowering plants (303 A.R.W.), of which 248 (251 A.R.W.) are found in Australia, and of this number 146 range into Western Australia. But of these, no less than 114 genera are more or less widely distributed outside the Australasian region, leaving only 31 genera, peculiar to New Zealand and Australia, which range into Western Australia. I append the names of these genera below,* but my knowledge of the Australian flora is much too limited to enable me to say how many of them have their head-quarters in Eastern or how many in Western Australia. In this connection greater interest attaches to those species which occur in both New Zealand and Western Australia. There are altogether 215 New Zealand species (belonging to 134 genera) found in Australia, many of them being antarctic or South American forms which occur very sparingly on the mountains of Victoria and Tasmania. Of these 215 species, 106 (belonging to 79 genera) range into Western Australia, but subtracting 68 species (52 genera) which have a very wide distribution, we find that we have still 38 species of limited dispersion to consider. Of these 24† belong to genera whose head-quarters are outside of Australia, and their spread into Western Australia is probably more recent than into New Zea-
[Footnote] * New Zealand genera confined to New Zealand and Australia, which occur in Western Australia:—1, Pittosporum; 2, Plagianthus; 3, Phebalium; 4, Stackhousia; 5, Pomaderris; 6, Discaria; 7, Swainsonia; 8, Leptospermum; 9, Actinotus; 10, Olearia; 11, Brachycome; 12, Craspedia; 13, Cassinia; 14, Ozothamnus; 15, Scævola; 16, Draco-phyllum; 17, Logania; 18, Persoonia; 19, Pimelea; 20, Poranthera; 21, Prasophyllum; 22, Pterostylis; 23, Cyrtostylis; 24, Caladenia; 25, Arthropodium; 26, Leptocarpus; 27, Calorophus; 28, Microlæna; 29, Deyeuxia; 30, Echinopogon; 31, Schædonorus.
[Footnote] † 1, Ranunculus lappaceus; 2, R. plebeius; 3, R. rivularis; 4, Claytonia australasica; 5, Linum marginale; 6, Pelargonium australe; 7, Tillæa purpurata; 8, Myrio-phyllum variæfolium; 9, M. pedunculatum; 10, Epilobium glabellum; 11, Daucus brachiatus; 12, Senecio lautus; 13, Microseris forsteri; 14, Sebæa ovata; 15, Myosotis australis; 16, Mimulus repens; 17, Salicornia australis; 18, Carex inversa; 19, Deyeuxia forsteri; 20, D. quadriseta; 21, Danthonia semi-annularis; 22, Schædonorus littoralis; 23, Glyceria stricta; 24, Bromus arenarius.
land; 7* belong to genera which are chiefly found in Eastern Australia, from whence the species in question have probably spread themselves east and west; and 7† more are of genera of which I do not know the centre of dispersion.
A close examination of the whole leads strongly to the conclusions that the basis of the floras of Eastern Australia and New Zealand are somewhat identical; that both have received immigrants independently after their separation, from north and south,—Australia by reason of its northern land connections with New Guinea receiving the greatest number of tropical species, and New Zealand from its southern extension the greatest number of antarctic and American species; that the West Australian flora proved more aggressive than the Eastern, and thus overran the whole continental area, giving it its peculiarly characteristic facies; and that of the Eastern species only those having considerable powers of dispersion have succeeded in spreading themselves westwards.
In considering the geographical distribution of a flora it is usual to bring under review only the phanerogamic or flowering plants, because the spores of Cryptogams furnish them with a most remarkable power of dispersion by wind. Yet even the distribution of our ferns and other vascular Cryptogams bears its testimony in support of the theory of the origin of the flora enunciated by Mr. Wallace. Excluding the endemic species there are about 30 per cent. of remaining forms which are spread extensively over a great part of the globe, about 4 strictly American, another 30 of tropical, Asiatic, or Polynesian occurrence, and about 36 per cent. almost exclusively Australian. Of the 85 species common to New Zealand and Australia, only 15 occur also in West Australia, and these are all species of very wide and general distribution.
In bringing to a conclusion these somewhat disconnected remarks, I shall endeavour to show how they may be pieced together so as to give some idea of the present standing of the whole question. In examining such a matter, some starting point or line of demarcation must be taken, for were we to go far enough back we should have to account for the very existence of flowering plants themselves. There are those who believe that all our species have been produced by development from a few forms originally created in this region of the world, while others ignore the idea of
[Footnote] * 1, Vittadinia australis; 2, Erechtites prenanthoides; 3, Erechtites arguta; 4, Erechtites quadridentata; 5, Pterostylis squamata; 6, Microlæna stipoides; 7, Echinopogon ovatus.
[Footnote] † 1, Poranthera microphylla; 2, Thelymitra longifolia; 3, Schænus axillaris; 4, Cladium glomeratum; 5, Cladium gunnii; 6, Dichelachne stipoides (Stipa teretifolia); 7, Dichelachne crinita.
development altogether. Wherever flowering plants did originate, it was most probably not in New Zealand; and all the information we possess on the subject leads to the conclusion that the parent forms of our flora were introduced from other lands during a long succession of ages, and that the process is still going on.
As has been already stated, there are about 1085 species of flowering plants known to occur in these islands, and of this number about 800 are endemic, that is, confined to this region. The relative numbers given in Hooker's “Flora Novæ-Zealandiæ” are 730 and 507, but the additions during the last thirty years have chiefly been of endemic forms. These species have been developed by the peculiar conditions to which the parent forms have been subjected during long periods of isolation. What these conditions have actually been we do not know, but in the majority of cases the changes brought about have only been of specific value. Even where they amount to generic importance the affinities can in nearly every case be traced, and we can form an approximately correct opinion as to the relationships indicated.
The greatest proportion of these endemic species is of distinctly Australian origin; there are also a number showing Polynesian affinities, and many of antarctic relationship. The remarks therefore which apply to the plants common to New Zealand and the regions specified, will apply to the originals from whence our endemic species have sprung. In accounting now for the species which are common to New Zealand and other parts of the world, we may notice first, that there is no absolute need on the part of the botanist, as there is on the part of the zoologist, to assume the existence in long past ages of former land connections with countries lying round about. But we have now reason to believe that there were former land extensions, which served to widen the area of New Zealand as it existed in olden times, and to bring it into closer proximity with other countries. From the antarctic circle a constant succession of south-westerly and southerly winds and currents may have served from time to time to convey seeds, and birds carrying seeds in their crops and attached to their feet, etc.; while icebergs may have aided in carrying masses of earth, spores, and seeds of certain antarctic species of plants. The antarctic continent, of which the now existing portions are probably only fragments, had in all likelihood alternations of climate such as we know to have existed at its antipodes, and during some of its warmer epochs it would be invaded by plants from South America. These would thus become spread round the south pole, from thence to be distributed radially to the countries lying north, as the climate again altered. Not only would antarctic forms thus find their way into New Zealand, but it is by this means that South American forms were likely
introduced, and it is by this spreading north from a common centre that we must account for so many species which are found both here and in the Tasmanian and Australian alps. Why some species should become modified and others remain persistent, I do not know. Thus our Fuchsias and pepper trees are distinct from the species found in South America, though certainly derived from that region, while our tutu plants (Coriaria angustifolia and thymifolia) are identical with others found on the Andes. We cannot work out these problems with our present information, for the necessary factors are wanting.
The northern extension of New Zealand indicated by Mr. Wallace as existing formerly, would bring it into very close proximity to North-eastern Australia, which may then have been in form of a long, narrow island, running nearly north and south; and also close to extensive sub-continental areas, of which only the remains are now left in the Polynesian Islands. And not only did those forms which are common to New Zealand and Australia, and New Zealand and Polynesia, find their way thus southwards, but it was probably by this chain that the plants of European and Asiatic affinity now found in our islands were introduced. But it was only at a much later period that an upheaval took place of the comparatively shallow seas separating the eastern and western portions of Australia; and that those forms now so characteristic of Australia, and which had been long developing under the peculiar conditions of their isolation in the western portion, overran the whole continent and stamped their features so markedly on its flora. And it is to this explanation that we must look in accounting for the presence of so many plants in New Zealand and Eastern Australia which are not found at all in Western Australia. A few specially Australian plants may have at later periods found their way into this colony, as the prevalent winds here are from the west, and birds are still found which have apparently strayed across the intervening expanse of ocean, but their number must be almost inappreciable, and cannot affect the general result.
While many of the immigrants thus introduced may have transmitted their characters almost unaltered through many successive generations, so that we still rank their descendants as belonging to species yet to be found outside New Zealand, others gave rise to variations and sports, and in course of time the accumulation of these variations has amounted to specific importance, and in some cases even to generic.
I believe that some such explanation as that sought to be given here, will account for the present geographical distribution of our flora, but it will be long before we can trace the parent forms of many of our plants, and detect the alterations and variations they have undergone. A knowledge of
the tertiary and secondary floras of New Zealand and Australia will help much towards elucidating this problem, but the palæo-botany of this part of the world is yet in its infancy, and very little is known on the subject.
It may be considered that too much stress is laid in this explanation on the elevation and subsidence of great masses of land, but a little consideratien will show that this is not the case. The deeply gouged-out character of our western lakes and sounds shows that they were cut out by ice, and to account for this we must either assume that the land stood very much higher than it does now, or the climate was very much more frigid. But even in the latter case we must assume a considerable elevation, as glacier action would cease at or very near sea-level, and our sounds are gouged down to great depths below present sea-level. Further, most of the low-lying eastern portions of this island have been formed at comparatively recent times by the denudation of our mountain chains, and most of this eastern coast is rapidly—one might almost say visibly—rising out of the sea. Again, the occurrence of fringing and barrier reefs in tropical seas is an almost certain mark of subsidence, as coral zoophytes cannot live at greater depths than about 120 feet, so that when we find these hugh masses of rock surrounding islands, and standing out of an ocean in some cases 1,000 fathoms or more in depth, we are bound down to the conclusion that the base on which the zoophytes commenced their labours was only a few fathoms from the surface, though now 6,000 feet deep.
In bringing these remarks to a close, I may just point out that a probably most important factor has been throughout left out of our calculations, viz., the physical changes which have affected the whole of our globe during comparatively recent geological epochs. Many theories have been advanced of late years to account for the glaciation of parts of the northern hemisphere, and the theorists have in some cases called in as auxiliaries all the powers of heaven and earth. But we may be sure that whatever causes could lead to results which are so apparent in one large portion of the world, must have at the same time caused great alteration in all other parts. But until we know with more certainty than we do at present what these great causes were, we cannot estimate what their effects on this portion of the world have been.