Chapter XIV, there is rarely anything to suggest a derivation of the

inland from the coast species, both being, from the standpoint of dispersal, of independent origin.

About half of the plants have fleshy or sappy fruits (drupes and berries) that would attract frugivorous birds, such as we find in Xylosma, Elæocarpus, Eugenia, Scævola, Wikstrœmia, &c., whilst the others have often dry capsular fruits, with minute seeds as in Metrosideros, or with larger seeds as in Dodonæa. Some of them, like Pisonia, have fruits that excrete a viscid material that causes them to adhere firmly to plumage. Birds both granivorous and frugivorous have been actively at work; and there are few difficulties relating to dispersal connected with the genera, except with such as Gossypium and Elæocarpus.

I will adopt the method employed in the preceding chapter of discussing in detail from the standpoint of dispersal some of the genera that came most frequently under my notice, or in which I am greatly interested, and of dealing briefly with some of the rest. Those dealt with in other connections will not be treated.

ELÆOCARPUS (Tiliaceæ).

This is a genus of trees containing, according to the _Index Kewensis_, about 130 species, most of which are confined to tropical Asia, including Malaya; but a fair number occur in the Pacific region, in Australia, New Zealand, and the islands of the tropical Pacific, and the genus is also found in Japan. It will thus be seen that Elæocarpus is not only a continental but also a typical insular genus. It has reached not only some of the most isolated island-groups of the Pacific, but it is to be found also in the smaller islands of the Indian Ocean, there being an endemic species in Mauritius. Amongst the Pacific Islands, a region with which we are more immediately concerned, it has been recorded from the Solomon Islands, New Caledonia, Fiji, Tonga, Samoa, Rarotonga, and Hawaii. It is strange that the genus is not accredited to Tahiti, but since it is represented in Rarotonga we may regard it as not altogether absent from East Polynesia. Reinecke does not include it amongst the Samoan plants, but Horne, in a short list of plants collected in Upolu about 1878, mentions Elæocarpus græffei, a Fijian species (_Year in Fiji_, p. 285).

New Caledonia represents the principal centre of the genus in the tropical Pacific, thirteen species being accredited to it in the _Index Kewensis_. Seemann found six species in Fiji, a number that does not seem to have been added to by Horne. Of these one is found in Tonga and Samoa, and of the rest perhaps most are peculiar; but one of them is closely allied to a second peculiar Tongan species. Tonga possesses the two species just alluded to, whilst Rarotonga and Hawaii have each a peculiar species.

From an interesting comparison made by Mr. Burkill of some of the Polynesian species, it would seem that Elæocarpus, if not actually possessing a widely-spread polymorphous species in the tropical Pacific, presents us with the next stage in the differentiation of the species. Thus, he says in his paper on the flora of Vavau that an endemic Tongan species, E. tonganus, is allied to three different species—E. græffei from Fiji, E. floridanus from the Solomon Group, and E. glandulifer from Ceylon—three species, he remarks, which are “so closely allied that it is possible to regard them as insular subspecies.” It would thus appear that some of the species of the Western Pacific are almost in touch with Asiatic species. It would be of importance to determine whether some affinity can be detected between the species of this part of the Pacific and some of the widely-ranging species of Indo-Malaya, such as E. ganitrus and E. oblongus. Mr. Burkill goes on to say that the solitary Hawaiian and Rarotongan species are closely allied, an inference which is of interest as indicating the route by which Hawaii received its species. The genus, we may fairly infer, once possessed a widely-ranging polymorphous or very variable Asiatic species in the tropical Pacific; and we see it now in the next stage of specific differentiation in various far-removed regions. In this connection Seemann significantly remarks that all the Fijian species are evidently very local in the group.

It will be appropriate here to refer briefly to the station and mode of occurrence of the species. They occur most typically as forest-trees, often of considerable height. In New Zealand, according to Hochstetter, they form a feature in the temperate rain-forest; and, as we learn from Kurz, they are similarly conspicuous in the tropical rain-forests of Pegu. To this seeming indifference to the varying thermal conditions of different latitudes we shall have subsequently to refer again. The tree of the Hawaiian Group, as Hillebrand tells us, is common in the forests of Oahu and Kauai, but is scarce in Maui and Hawaii, a singular distribution that may be due to the inflorescence being “often monstrously deformed by oviposition of some dipterous insect.” The Rarotongan species, according to Cheeseman, is common throughout the island from the sea-level to the tops of the hills. In Vanua Levu I found that these trees preferred the crests of wooded mountain-ridges or the partially vegetated mountain peaks. They came under my notice in the forests of the island of Fauro, in the Solomon Group, associated with other large trees of the genera Canarium and Calophyllum.

Much interest is attached to the mode of dispersal of this genus, since in some species the size of the drupes and of the included “stone” is so great that, judged by those species only, it might be deemed impossible to attribute the existence of the genus in isolated oceanic groups to the agency of frugivorous birds. We are, however, compelled to appeal to the bird, since, as my experiments in Fiji indicate, the genus has little or no capacity for dispersal by currents, the “stone” when containing a seed always sinking, whilst the entire fruit either sinks at once or floats heavily for a few days.

The degree of fleshiness of the drupes of Elæocarpus varies in different species, being sometimes slight and at other times pronounced, but, speaking generally, they would be expected to attract frugivorous birds. The colour of the fruits of some species is dark and purplish, whilst in others it is a bright blue. In the last case the fruits are very conspicuous and sappy. A Solomon Island species collected by me and a Malayan species observed by Ridley had bright blue fruits, and Cheeseman refers to the Rarotongan species as possessing fruits of this hue. Their colour, therefore, would often aid in attracting birds, and we are not surprised to learn that they form a favourite food with fruit-pigeons, parrots, and other frugivorous birds in different regions. Amongst the fruits found by Professor Moseley in the crops of fruit-pigeons in the Admiralty Islands were those of Elæocarpus; whilst in the Solomon Islands I noticed that the blue fruits of the “Toa,” a species of the genus, were a favourite food of the same birds (_Bot. Chall. Exped_., iv. 307, 308; Guppy’s _Solomon Islands_, 293, 295). We learn also from Hochstetter and from Sir W. Buller that the drupes of the “Hinau” (Elæocarpus) form a favourite food of the parrots and fruit-pigeons of New Zealand (Hochstetter’s _New Zealand_; Buller’s _Birds of New Zealand_).

The question of size acquires considerable importance when we come to consider the transport of the seeds of the genus to a group of islands lying, like Hawaii, in the middle of the Pacific Ocean. The protection of the seed is also another important matter. There can, however, be no doubt that the hard woody or often osseous “stone” sufficiently protects the seed. With regard to size, if we were to judge from the dimensions of the fruits of some of the Fijian species, where, as I found, the “stone” measures from 3 to 5 centimetres (1-1/4 to 2 inches) in length, we might be led to form a very erroneous opinion of the capacity of the genus for conveyance through the agency of frugivorous birds to Hawaii. But when we turn to the Hawaiian species we find the difficulty much diminished, though still serious, the fruits being smaller and possessing a “stone” 2-1/2 centimetres or about an inch long. In other regions, however, the genus may possess fruits yet smaller in size. The Tongan endemic species, as described by Burkill, has fruits 1·7 cm. or 7/10 of an inch in length; and closely similar dimensions are given by Kirk for a New Zealand species. In both these cases the “stone” would not be more than half an inch or 1·2 cm. in length, and this would also apply to the Solomon Island species above mentioned. In another New Zealand species, where the drupe is only half an inch, the “stone” would be still smaller. It is thus evident that the fruits of different species vary greatly in size in different regions, and that there is no difficulty in assuming that a small-fruited species could be dispersed over the Pacific by frugivorous birds, and carried either to Hawaii or New Zealand.

It might be an interesting point to determine to what extent a species in an oceanic island could effect its own isolation by developing a “stone” too large and too heavy to be transported across an ocean by birds, such as seems to have happened with some Fijian species. But a similar curious question is raised by the deterioration of a drupe in its capacity for dispersal by frugivorous birds, when, as in the case of the Hawaiian species of Elæocarpus, the drupes become dry and almost sapless. As remarked in Note 68, this same feature is to be noticed in the fruits of some of the Hawaiian endemic genera. This, of course, would be quite in accord with what we should expect from the standpoint of dispersal.

I will conclude these remarks on Elæocarpus with a reference to the similarity of its distribution with that of Freycinetia. Both genera are at home in the temperate rain-forests of New Zealand and in the tropical rain-forests of the Pacific islands and of Malaya. Their capacities for dispersal are so different and so unequal, the dispersal of Freycinetia being seemingly so much more readily effected, that we can only suppose that time has long since discounted any special advantage one genus possesses over the other as regards distribution.

DODONÆA (Sapindaceæ).

This genus of small trees and shrubs includes between fifty and sixty known species, of which about forty are confined to Australia; but a few species are found over the tropical and subtropical regions of the world, extending sometimes into temperate latitudes. There are, it seems, only three species known from the oceanic groups of the tropical Pacific: one, the cosmopolitan Dodonæa viscosa, that occurs in every island of volcanic formation; and two others associated with it in the Hawaiian Group, to which they are restricted. We have thus repeated in this genus what is true of several other genera in Hawaii, such as Metrosideros and Wikstrœmia, namely, the occurrence in that group of a widely-ranging species accompanied by other species peculiar to those islands. In the case of Dodonæa in Hawaii we should not expect to find it very difficult to connect the endemic species with the widely-ranging D. viscosa, which is a very variable species. The extreme forms in different parts of the world are so different in character that Bentham viewed this species as probably including the whole of the extra-Australian species, excepting perhaps the Hawaiian endemic species and one or two South African and Mexican plants (_Bot. Chall. Exped._, iii. 136).

Of the two Hawaiian peculiar species, one, Dodonæa eriocarpa, is a mountain shrub found in most of the large islands and occurring sometimes at elevations of 6,000 to 8,000 feet. The other species, D. stenoptera, is, according to Hillebrand, a very distinct species found only on Molokai. Bentham was only acquainted with the first-named, and his hesitation to include it as one of the innumerable forms of the widely-ranging D. viscosa is very suggestive. However, whether or not one or both of these peculiar forms are connected in their origin with this species, it is certain that the genus has been established for ages in Hawaii; and from D. viscosa we can learn how a species of the genus can cross an ocean, and also how from a widely-ranging species exhibiting extreme variability species peculiar to a group of islands could have been derived.

The great variability of Dodonæa viscosa is associated with great adaptability to different stations. Thus, as Mr. Hemsley tersely puts it, it is one of those plants that thrive on the sea-coast as well as inland, and in almost any soil or situation—provided, it may be added, that the station is well exposed to the sun. Although Mr. Ridley characterises it as a regular sea-shore plant in the Malay peninsula, and although Prof. Schimper places it in the Indo-Malayan strand-flora, it is as an inland plant that it is most characteristic of the Pacific islands; and the key to its powers of adaptation to different stations is to be found in its xerophilous habit. It is essentially a plant of sunny places, and is equally at home on the parched inland plain, in the open wood, on the sandy beach, on an old lava-field, or on rocky declivities. It is not a plant of the rain-forest, preferring dryness to humidity and sunshine to shade.

The following remarks on the mode of dispersal of the wide-ranging Dodonæa viscosa will serve to roughly indicate the capacity of the genus for distribution. It is a subject, however, that requires further detailed investigation. The light, inflated, winged capsules of this species, about an inch across, could be blown for long distances along the ground and carried for short distances in the air by strong winds, but, as is also remarked by Prof. Schimper (_Ind. Mal. Strand-flora_, p. 157), they are much too large to be transported by winds across a broad tract of sea. The currents, however, may have aided in the dispersal of the species in the case of island-groups 500 or 600 miles apart. Although the membranous capsules before dehiscing would be unable to withstand the “rough-and-tumble” of ocean-transport for more than a few days, the seeds possess some floating powers of a purely accidental nature due to the imperfect filling up of the seed-cavity in some of the seeds. In an experiment made in Hawaii I found that only half the seeds floated in sea-water. Prof. Schimper, in an experiment conducted in Germany with seeds that must have been well dried by keeping, found that they floated for from ten to sixty days. This limited capacity for flotation might possibly allow the species to reach Tahiti by easy stages from Fiji; but it is not sufficient to explain its occurrence in the more isolated Hawaiian Group. The fruits and seeds of this plant never, however, came under my notice in the floating or stranded seed-drift of Fiji; and I am not inclined, for this and the reasons above mentioned, to consider that the currents have been very effective agents in dispersing this plant over the Pacific islands.

Hillebrand endeavoured to account for the wide distribution of Dodonæa viscosa by “the glutinous capsules which would easily adhere to the plumage of birds.” It may be here remarked that in the dried state specimens of the plant have a varnished appearance as respecting the leaves, branchlets, and capsules. In the living condition this is represented by a glutinous or viscid condition of the surface of these portions of the plant, rendering them adhesive to the touch. I found, however, that only the immature capsules are markedly “sticky,” and that in any case the adhesive power was quite insufficient to allow of adherence for any length of time of fruits of this size to a bird’s feathers. Mr. Ridley, who allows much latitude to birds in matters of dispersal, remarks that the stickiness only appears when the specimen is dry (_Trans. Linn. Soc. Bot._, 1888-94, p. 289). It is, nevertheless, likely that the crustaceous seeds, which do not exceed 1/5 of an inch (5 mm.) in size, when swallowed by a bird granivorous in its diet, might be voided unharmed, and the dispersal of the species assured. It is in this fashion, I imagine, that the plant reached distant groups like Tahiti and Hawaii.

There is, of course, the possibility that man has in past times aided in the distribution of Dodonæa viscosa over the warmer regions of the globe. But such an agency seems largely discounted in the case of an isolated archipelago like Hawaii by the occurrence of endemic species. Nor does the usual station in the Pacific islands support the view that it was introduced by the aborigines. According to Hillebrand, it possesses a variety (var. spathulata) in Hawaii which seems also to occur in Tahiti and New Zealand. Nadeaud observes that in Tahiti it grows as a bush on dry crests, and as a small tree, ten feet in height, in the mountains.

Nor do the aboriginal names of Dodonæa viscosa point in the direction of man’s agency. It possesses a different name in every group, and is evidently not a plant with which the ancestors of the Polynesians were familiar in the home of the race. Thus it is named “aalii” in Hawaii, “apiri” in Tahiti, “ake” in Rarotonga, “lala vao” in Samoa, and I may add “usi” or, as Seemann writes it, “wase” in Fiji.

Looking at these various facts, I am not inclined to exclude altogether any one of the three agencies above discussed; but I should imagine that, placed in their order of effectiveness, we should have first birds, then the currents, and lastly man.

METROSIDEROS (Myrtaceæ)

Whilst this genus of trees and shrubs has its home in New Zealand and Australia, there is an extremely variable Polynesian species, Metrosideros polymorpha, ranging over all the volcanic groups of the tropical Pacific, from Fiji to Pitcairn Island and from Hawaii to the Kermadec group, but seemingly only in the Hawaiian group associated with endemic species. According to the _Index Kewensis_ the genus comprises about forty known species, of which two-thirds are confined to New Zealand and Australia in equal proportions; whilst, among the rest, six species belong to New Caledonia, two to Hawaii, and three to Malaya, and there are solitary species in Chile, Madagascar, and South Africa.

I will attack the problem connected with the distribution of the genus through the widely-ranging Polynesian species, Metrosideros polymorpha. “This genus,” wrote Dr. Seemann, “is in a fair way of becoming in Polynesia what Rubus is in Europe. It is very much given to variation, and it is very difficult to find out the limits of the different species.” In making these remarks he had this species in view, and his adoption of Gaudichaud’s specific name of “polymorpha” to cover almost all the Polynesian forms has been generally followed. Although so widely distributed over the Pacific, it is in the Hawaiian Islands that this tree attains its greatest development, growing gregariously and often forming almost exclusively entire forests; and it is here that it displays the greatest variation. But it was remarked by Seemann, and this was confirmed by Hillebrand, that almost all the Hawaiian forms occur in the Society or Tahitian Islands.

In connection with the great variability of Metrosideros polymorpha must be considered its variety of stations and its great range in altitude. Hillebrand describes seven Hawaiian forms of this species, and their various stations and characters are well illustrated in his descriptions. Thus, whilst the trees may attain a height of forty feet in the forests, in elevated exposed situations they may be small and gnarled or low and shrubby; whilst in the bogs and swamps of the high levels of Maui and Kauai the plant grows as a prostrate shrub. It is not at all unlikely that the two peculiar Hawaiian species of the genus had a common origin from a widely-ranging species, which, if not the present M. polymorpha, was its immediate ancestor. One of them was, indeed, included by Dr. Seemann within the wide limits of this species, and the other was accepted with a doubt.

To illustrate the great vertical range in the Hawaiian Group of Metrosideros polymorpha, I will take it as I found it in the island of Hawaii. Here it ranges from the coast up to about 8,000 feet above the sea. But it is in the middle forest-zone at elevations of 2,000 to 4,000 feet, where it is often associated with the Koa and Olapa Trees (Acacia koa and Cheirodendron Gaudichaudii), that it is most at home and attains its greatest size. Higher up at heights of 5,000 to 7,000 feet in the more open forests it is still in the company of the trees just named together with Sophora chrysophylla and Myoporum sandwicense. At 8,000 feet it becomes very stunted and is accompanied usually by bushes of Cyathodes and other plants of similar bushy growth. In the lower parts of its range, from 2,000 down to 1,000 feet, it forms forests with the Kukui Tree (Aleurites moluccana), mingled also with smaller trees such as the Hawaiian Olive (Osmanthus), and the Kopiko (Straussia). Below 1,000 feet, and wherever bold promontories reach the coast and the inland forest descends to the sea, we find it associated with such trees and shrubs as the Lama (Maba sandwicensis) and different Akeas (Wikstrœmia). On the partially vegetated surfaces of old lava-flows near the coast it grows beside bushes of the Ulei (Osteomeles anthyllidifolia) and of Cyathodes.

Compared with its behaviour in Hawaii, Metrosideros polymorpha takes a relatively unimportant part in the vegetation of Fiji. As Horne observes, the trees are most common in the dry parts of the two largest islands and grow in the poorest soil. I found them in Vanua Levu usually in open exposed situations, generally in the dry “talasinga” plains on the north side of the island, where they were associated with Acacia Richii, Dodonæa viscosa, and Casuarinas; and sometimes they occurred in a shrubby form on the rocky peaks of the highest mountains. In Rarotonga also, as we learn from Cheeseman, it is on the tops of the rocky peaks and along the crests of the ridges that this species, which is abundant in the island, is frequently found.

I may here allude to the curious fact observed by me on the upper open wooded slopes of Mauna Kea at elevations of 6,000 to 7,000 feet, and therefore on the outskirts of the true forest-zone. Here the Ohia Tree, as the Hawaiians name Metrosideros polymorpha, often grows in close association with the Olapa Tree (Cheirodendron Gaudichaudii). In one locality, for instance, a large Olapa was growing in the fork of an Ohia at about eight feet from the ground, and sending down roots on either side. Sometimes the trunks of the Olapa and the Ohia were to be seen growing in such close contact as to look like one tree. In one such case a young tree, four feet high, of Myoporum sandwicense was growing in a fork of the Ohia, whilst in a fork of the Olapa a plant of Vaccinium penduliflorum, three or four feet in height, had established itself. This remarkable instance of epiphytic growth also proved to be quite a revelation with regard to the dispersal of seeds in this island. Amongst these four associated plants, which include three trees and one shrub, all except the Ohia, which was probably the original tree, have fruits that would attract frugivorous birds; and in succession these birds had first dropped a pyrene of the Olapa in the fork of the Ohia, and afterwards the seeds of Myoporum again on the Ohia, whilst finally the Vaccinium seeds were dropped into the fork of the Olapa after it had developed into a tree.

The mode of dispersal of the seeds of Metrosideros polymorpha now invites our attention. Since the fruits are dry, dehiscent capsules possessing minute fusiform seeds, we are not able to appeal directly to the agency of frugivorous birds to explain the wide dispersal of this species. The seeds are light in weight and remind one a little of those of the succulent fruits of Freycinetia. For purposes of dispersal, however, they must be placed in the same category with other plants with dry, dehiscent fruits and small seeds, such as the Vota (Geissois ternata) of Fiji, a tree that in those islands grows in similar stations. On a later page I have suggested that the seeds of the Vota are dispersed by large bats that visit the trees for the sake of the honey in the red flowers. With Metrosideros polymorpha birds act probably in the same way. We are, in fact, informed by Mr. Perkins that the nectar-feeding birds of the Hawaiian Drepanids now obtain their main supply of this food from the blossoms of this tree. If bats or birds visit the large red flowers of Metrosideros polymorpha for the same purpose, it is not difficult to imagine that they might carry away in their fur or in their plumage some of the small seeds shaken out of old dehiscent capsules. In this connection we may note that the Kaka Parrot (Nestor meridionalis) of New Zealand is said to feed largely on the scarlet blossoms and nectar of Metrosideros robusta (Evans’ _Birds_, p. 374).

The seeds of Metrosideros polymorpha might no doubt be carried by winds from one mountain-top to another and across narrow straits, but only whilst adherent to a bat or a bird could they be carried across a wide tract of ocean. Speaking of the genera Metrosideros and Lobelia in connection with their occurrence in the Kermadec Islands, Sir J. Hooker long ago referred to their minute seeds as not adapted for transport across oceans unless their minuteness and number fitted them for it (_Journ. Linn. Soc._, i. 127). The point that is raised here for these genera in the Kermadec Group can be raised for the same two genera in Hawaii and for a multitude of other small-seeded genera in those islands.

ALYXIA (Apocynaceæ).

This genus of climbing or straggling shrubs tells its own story of the widely dispersed Indo-Malayan genera in the Pacific islands. Containing about forty known species, it is distributed over the tropical regions from Madagascar and the Mascarene Islands eastward to the Paumotu Group and Pitcairn Island in mid-Pacific, and has its focus in the area comprised by Malaya, Australia, and New Caledonia. In the _Index Kewensis_ about eight species are assigned to New Caledonia, seven to Australia, and seven to Malaya. One species, Alyxia stellata, ranges over nearly the whole of the area of the genus from tropical Asia, through Malaya, across the South Pacific to Tahiti. It will be for the future investigator to determine how far the present distribution of the genus can be connected with one or two widely-ranging polymorphous species. The data at my disposal seem to show that in the open Pacific, at all events, the history of the genus has gone a step beyond this stage.

Of the seven or eight species recorded from the Pacific islands east of New Caledonia, only two or three seem to be now recognised as restricted to particular groups, namely, one in Hawaii (Schumann), one in Fiji, and one in Rarotonga. The other species indirectly connect together all the groups, although no single species occurs over the whole region. Thus the Hawaiian species, Alyxia olivæformis (Gaud.) has in recent years been found in Upolu, in the Samoan Group, by Dr. Reinecke, an exceedingly interesting though unusual specific link between these two archipelagoes. Two species, A. stellata and A. scandens, range over the South Pacific from Fiji to Tahiti, the last-named also occurring in the Paumotu or Low Archipelago; whilst Rarotonga possesses a form closely allied to the first-named, and to it Cheeseman has given specific rank. Another species, A. bracteolosa, links together the contiguous Fijian, Tongan, and Samoan groups. This distribution is what we should have expected if one or two polymorphous species had originally ranged over the Pacific and were advancing towards that stage of differentiation when each group possesses its own peculiar species. (It may be here remarked that an undetermined species of Alyxia is accredited by Maiden to Pitcairn Island, which indicates that the genus has extended east in the Pacific almost as far as the extreme limit of the Polynesian region.—_Australas. Assoc. Reports_, Melb., 1901, viii.)

All visitors to these islands that are interested in their floras will be familiar with the Alyxias; and there are few of their plants that the natives take more pleasure in pointing out to white men. They are readily recognised on account of their black moniliform drupes and their milky sap. All over Polynesia, whether in Hawaii, Tahiti, Samoa, or Fiji, the aborigines value the plants on account of the delicate fragrance of their foliage and bark. These materials they use for personal decoration and in making wreaths, stripping off the bark of the young branches with their teeth in the same fashion in Fiji and Hawaii and probably in all the Pacific islands. Throughout Polynesia, excluding Fiji, they bear the same name, which takes the form of “maile” in Hawaii and Samoa, and of “maire” in Tahiti and Rarotonga—a name which the Maoris, remembering the Alyxias of their tropical home in the South Pacific, have applied to New Zealand species of Olea and Eugenia. The Fijian generic name for Alyxia is “vono.”

A word may be said about the station of these plants in the Pacific islands. In Hawaii they occur in the middle and lower forests, and usually between 2,000 and 4,000 feet in elevation. In Tahiti they frequent the crests and precipitous rocky slopes of the mountains at elevations of from 3,000 to over 6,000 feet. The Rarotongan species often forms extensive thickets in rocky localities on the hills. In Samoa they are found usually in the mountain forests. In Fiji they grow on the outskirts of the virgin forests and on rocky sparingly vegetated mountain peaks. I found them often in Vanua Levu growing amongst the open vegetation on the summits of isolated mountains at elevations of 2,000 to 2,500 feet, where they were associated with other plants like Elæocarpus, Pleiosmilax, and Scævola, possessing similar fleshy fruits likely to be dispersed by frugivorous birds.

The Alyxias indeed seem well suited for dispersal by birds. The black fleshy drupes would readily attract them; and the solitary seed protected by a very tough horny albumen might be ejected unharmed in their droppings.

--------------

It would be possible to enter into similar detail with several other genera of this period; but here I can only direct attention to their principal indications, permitting myself a little more license when discussing the means of dispersal.

ALPHITONIA (Rhamnaceæ).—Amongst other genera with polymorphous species closely following the lines taken by Metrosideros in the Pacific is Alphitonia, a small Malayan and Polynesian genus of tall trees, containing at most three or four species, one of which (A. excelsa) has almost the range of the genus and is found in most of the Pacific archipelagoes. So variable is this widely-ranging tree that Bentham suggested that there was only one species in the genus (_Bot. Chall. Exped._, iii. 133), a suggestion especially interesting in connection with the _rôle_ taken by polymorphous species in the Pacific. As bearing on the mode of dispersal of this species, it may be observed that my Fijian experiments show that the fruits are not fit for transport by currents. With the mature drupe the outer coverings become pulverulent, and the fruit breaks down, freeing the pyrenes which do not float; nor have the seeds any buoyancy. Although the dry drupes would seem unattractive to birds, it is to birds we must look for the dispersal of the genus.

PISONIA (Nyctagineæ).—Like Dodonæa, Metrosideros, and Alphitonia, the cosmopolitan genus Pisonia possesses a polymorphous species that displays its variation in every Pacific group and occupies a considerable number of stations. The earlier botanists in the Pacific differed much as to the species of this region, and this led Mr. Hemsley to observe in his paper on the Tongan flora that it is difficult to understand the various Polynesian and Australian species except on the assumption that there is one very variable species. Recognising this difficulty, Drake del Castillo deals somewhat summarily with nearly all these forms, uniting them under one comprehensive species, P. umbellifera (Seem.), thus constituting “une espèce très-polymorphe” that ranges (generally in maritime districts) over tropical Asia and the islands of the Indian and Pacific Oceans, extending to North-East Australia and to New Zealand. On account of the unusual capacity for dispersal possessed by this species—a subject to be immediately discussed—the tendency to specific differentiation has been kept in check, though the process has gone farther in some groups than in others, as in the case of Hawaii, where Hillebrand’s endemic species has, however, been included by Drake del Castillo in his polymorphous species, P. umbellifera.

The fruits of this genus possess no capacity for dispersal by currents. They never came under my notice either in floating or stranded seed-drift, and have little or no buoyancy. Prof. Schimper, experimenting on the well-dried fruits of Pisonia aculeata, a seaside shrub common in America and in the Old World, and destined probably to be brought by the systematist into touch with the polymorphous P. umbellifera, found that they sank in a day or two (_Ind. Mal. Strand-flora_, p. 156). Dismissing the agency of the current, he looked to that of the bird for the explanation of the dispersal. The probability of the effectiveness of this last-named agency has long been surmised. It attracted the notice of Darwin and especially invited the attention of another student of plant-dispersal, Dr. H. O. Forbes. The long, narrow, often fusiform fruits are invested by a somewhat coriaceous perigone and range from less than an inch to three inches in length (2-7·5 cm.). They excrete a very viscid fluid often in quantity, and sometimes also possess glandular spines. The Hawaiians, according to Hillebrand, used this material as bird-lime for catching birds, and the fruits, he says, will stick fast to the paper in the herbarium for years. In that group I often found the fruit adhering firmly to my clothes. Writing of these trees on Keeling Atoll, Forbes observes that their sticky fruits are often such a pest to birds roosting in their branches that they have proved fatal to herons and boobies by collecting in their plumage. “It is easy to perceive,” he remarks, “how widely this tree might be disseminated by the birds that roost on it” (_The Eastern Archipelago_, p. 30). In New Zealand, as we learn from Kirk, the viscid fruits of Pisonia brunoniana attract small birds which become firmly caught and die miserably. A cat has been known to wait under a tree watching its opportunity of preying on the entangled birds. Sir W. Buller states that the New Zealand fruit-pigeon feeds at times on the green fruits of P. umbellifera; and we can infer that it occasionally carries off some of the riper fruits in its feathers.

WIKSTRŒMIA (Thymelæaceæ).—This is a small genus of shrubs and small trees, with red or yellowish drupes fitted for dispersal by frugivorous birds, that is confined mainly to tropical Asia, Australia, and Polynesia. Following Seemann and Drake del Castillo, we may say, that like several other genera of this period, this genus possesses in the tropical Pacific a widely-ranging species, W. indica, that occurs in Hawaii, the Marquesas, Tahiti, Samoa, and Fiji, growing amongst the vegetation immediately behind the beaches and in the plains and open wooded districts inland. In Hawaii it is associated with half a dozen peculiar species, and in Tonga there is also an endemic species. The widely-ranging species has its home in the Indian Archipelago and in the Asiatic mainland, and occurs also in Australia. According to Gray, the American botanist, it is represented by a different variety in almost every group in the tropical Pacific, and it presents us therefore with another example of a polymorphous species which links Polynesia directly with Malaya. As bearing on the dispersal of the genus by birds, it may be added that Mr. Perkins in the _Fauna Hawaiiensis_ speaks of some of the Drepanids and of a species of Phaeornis as feeding at times on the fruits of these plants.

PEPEROMIA (Piperaceæ).—All observers of tropical plant-life will be familiar with this genus of low herbs growing on tree-trunks, on the soil, on rocks, and on stonewalls, and comprising about 500 known species distributed over the warmer regions of the globe and sometimes extending into cooler latitudes. In Polynesia it attains its greatest development in Hawaii, where Hillebrand enumerates about twenty species, of which, after excluding doubtful forms, at least a third must be endemic. Tahiti, Samoa, and Fiji are each known to possess three or four species, of which one is usually restricted to the group. Two species, P. reflexa and P. leptostachya, link together nearly all the groups of the tropical Pacific, including Hawaii, the first cosmopolitan, and the second hailing from North-East Australia and indicating that the genus has entered Polynesia from the west.... These plants possess spikes of small berries containing a single seed, and are evidently, like other Piperaceæ, dispersed by frugivorous birds. It is to be noted that the presence of a West Indian and Mexican species in the Bermudian caves is attributed by Mr. Hemsley to frugivorous birds (_Bot. Chall. Exped._, Introd. 49, i. 62). In Vanua Levu they occur on the bare rocky peaks of some of the mountains under such conditions that the seeds could only have been brought by birds. Thus, on the bare surface of a large block of tuff forming the highest peak of Koro-Mbasanga, 2,500 feet above the sea, I found only two plants, Oxalis corniculata and a species of Peperomia.

EUGENIA (Myrtaceæ).—This is a very extensive genus split up into different subgenera, and comprising some 600 or 700 known species scattered over the warm regions of the globe. Their fleshy, usually red, berries contain as a rule one or two large seeds, and attract birds and animals of all descriptions. The feature most interesting to us is the dispersal of the genus over the Pacific islands eastward to the Low Archipelago and northward to Hawaii. The track by which it has entered the Pacific from the west is indicated in the distribution of the species. The genus is only well represented in the Western Pacific, whilst eastward and northward of Samoa and Tonga the distribution is fitful and irregular, it being evident that the extension beyond these two groups has been accomplished with difficulty.

There are at least twenty-five species in Fiji, of which perhaps half would be peculiar; in Tonga eight species, of which two may be endemic; in Samoa thirteen species, of which four are peculiar; in Rarotonga none; in Tahiti a single non-endemic species; and in Hawaii two species, of which one is peculiar. Only truly indigenous species are here recorded, and Eugenia malaccensis, which has accompanied the aborigines in their migrations, is not included. A solitary species, E. rariflora, connects together all the principal archipelagoes from Fiji to Tahiti and the Gambier Islands, and northward to Hawaii. Nine species are known to be common to the region in which lie the three groups of Fiji, Tonga, and Samoa; and since some of these species occur in the groups further west they may be regarded as keeping up the connection with the original home of their ancestors in the Malayan region.

Looking at these facts of distribution of the genus Eugenia in the open Pacific, it is evident that whatever dispersal of the genus is now in progress in this ocean is mainly confined to an interchange between the groups of Fiji, Tonga, and Samoa in the Western Pacific, and doubtless between the islands further west of these groups. The smaller islands lying between and around these three groups participate in the distribution of the species common to all. Thus Wallis Island, according to Drake del Castillo, possesses two of these species. Over the rest of the ocean the dispersal of the genus seems to be no longer effective, since Eugenia rariflora, which links together Fiji, Tahiti, and Hawaii, shows signs of differentiation in nearly every group. In Hawaii, where it is very rare and is only recorded from two of the islands, it has developed a small-leaved variety. In Tahiti it displays the same variation; and Seemann observes that there are differences between the Tahitian and Fijian species which may be almost specific in value. It would also appear that both in Hawaii and Tahiti the fruits have become less attractive to birds, being described as “dryish” and “dry,” which is, as Dr. Seemann remarks, certainly not true of the Fijian plant.

In Fiji the Eugenias, as small trees and shrubs, find their home usually on the banks of streams and rivers, on the outskirts of forests, and occasionally at the coast. One of them, E. richii (Gray), is a characteristic littoral tree in the group. A tree near it in character was found by me of common occurrence in the interior of coral islets in the Solomon Group (_Solomon Islands_, p. 297). E. rariflora occurs also in the interior of coral islets in Fiji and amongst the vegetation at the back of the mangrove-swamps.

Coming to the mode of dispersal of the genus in the Pacific, I may remark that all the species, with the doubtful exception of the Fijian and Samoan Eugenia neurocalyx (the Lemba of Fiji), are wild trees and shrubs useless to man, but much appreciated by pigeons, pigs, &c., on account of their fleshy fruits. Since exact observations on the possibility of their dispersal by currents seemed to be wanting, I made some experiments in Fiji. Out of six species, which included E. corynocarpa, rariflora, richii, and rivularis, the mature fruits of most species sank in sea-water in from seven to ten days. However, those of the beach tree, E. richii, floated for a fortnight. The cause of sinking in all cases lay in the decay of the outer fleshy covering. As I have observed in river and sea drift, fish bite at the floating fruits, and in this manner the seeds would soon be liberated and sink. The seeds of all the plants sank at once in my experiments except with one species, where the seed loosely filled its test and thus a floating-power of a few days was acquired. Currents, it is apparent, could never account for the dispersal of the genus over a broad extent of ocean, though in a few cases, as in that of the littoral tree above noted, it is quite possible that the fruits could be successfully transported across a tract of sea 200 or 300 miles in width.

It has long been known that fruit-pigeons are fond of the fruits of wild species of Eugenia, and I found the Solomon Islanders and the Fijians well acquainted with the fact. The fruits of a tall Eugenia tree, near E. richii, common in the interior of the coral islets of Bougainville Straits in the Solomon Group, were found by me in quantities in the crops of fruit-pigeons shot by Lieut. Heming and Lieut. Leeper on the islets (_Solomon Islands_, pp. 293, 297; _Bot. Chall. Exped._, Introd. 46, iv. 312). Dr. Seemann remarks that in Fiji the red fruits of E. brackenridgei are eaten by pigeons. The somewhat thin coverings of the seeds of this genus would seem to offer but a slight protection in a bird’s stomach, though in one species the test was almost crustaceous.

Most species possessed only one or two large seeds in each fruit, though this number may vary in the same individual. Thus, out of ten fruits of Eugenia rariflora in Fiji, six had one seed, three had two seeds, and one had three seeds. In the fruit of E. neurocalyx, however, the seeds range from three to five.

It is the question of size that is of importance in considering the possibility of birds transporting the seeds over a broad tract of ocean. Eugenia rariflora, the species found all over the Pacific, has seeds that measure in the Fijian plant one-fourth to one-third of an inch (6 to 8 mm.) across; and in Hawaii, according to Hillebrand, they would perhaps be rather smaller. In point of size there is less difficulty with regard to the transport by birds across the ocean to Hawaii of the seeds of Eugenia rariflora than with the “stones” and seeds of some other genera, like Elæocarpus, Osmanthus, and Sideroxylon, that must have been conveyed there by the same agency. The fruits of several of the Fijian species are of the size of a large cherry; but it is noteworthy that in those species like E. corynocarpa and E. neurocalyx, where the fruits are large and the seeds about an inch in size, the plants are confined to the Western Pacific only, namely, to the Fiji-Samoa region.

There is therefore no difficulty, from the standpoint of size, in accounting for the distribution by birds of the widely-ranging Eugenia rariflora over Polynesia; but at first sight there seems to be a real difficulty with regard to the protective coverings of the seed. Yet Nature speaks with no hesitating voice in the matter. The West Indian and Florida species, E. monticola, regarded as indigenous in the Bermudas, must have reached that group through the agency of birds that carried its seeds over quite 800 or 900 miles of sea; and it may here be noted that South Trinidad, lying some 600 miles off the coast of Brazil, and Rodriguez, distant about 330 miles from Mauritius, each possess species (_Bot. Chall. Exped._, Introd., 12, i. 32, ii. 128). If fruit-pigeons can transport Eugenia seeds across 600 or 800 miles of ocean, there would be no difficulty in accounting for the stocking of the Fijian, Tongan, and Samoan Islands with the genus from regions to the west. But the occurrence of the genus in Hawaii seems to compel us to assume that the seeds have been carried in a bird’s stomach over 1,500 to 2,000 miles of ocean. This difficulty, however, does not really exist. Eugenia rariflora, the Polynesian species found in Hawaii, frequents, as before observed, coast districts and coral islets in Fiji, and if we suppose that the low islands of the Fanning and Phœnix Groups, lying between Hawaii and Samoa, have served as stepping-stones, a capacity of crossing 1,000 miles of ocean would be alone required. This is not much in excess of the distance that must have been traversed by the bird that first brought the seeds of Eugenia monticola to the Bermudas.

Other genera like Morinda and Scævola, possessing fleshy fruits dispersed by frugivorous birds, have been mentioned in different connections in other parts of this work, and will not be further dealt with here. But before concluding this chapter I will refer briefly to one of the disquieting mysteries in the flora of the Pacific which is presented to us in the genus Gossypium. Three species are, or were, truly indigenous in this region. One is Gossypium drynarioides, a small endemic tree found by Nelson, the companion of Captain Cook, in Hawaii, which was very rare in Hillebrand’s time, and is perhaps now extinct. The second is G. tomentosum (Nuttall), which is also peculiar to Hawaii, where it is found on the beaches. I am following here the _Index Kewensis_; but it should be remarked that this species occurs also in Fiji, though Seemann regards it as introduced. The third is G. religiosum (L.), found by Captain Cook’s botanists growing wild in Tahiti, and hailing from the tropics of the Old World. The seeds of the first species are covered with a short brownish tomentum, and could never have been of any value. The tawny wool of the seeds of the second species has a staple too short for cultivation; whilst the Tahitians do not seem to have made any use of the third species. It is difficult to draw any conclusion concerning the presence of these plants in the Pacific islands at the time of their discovery; nor can Dr. Seemann, who was especially well informed in these matters, aid us much in our endeavours to solve the mystery. From the aboriginal names we get no clue. The Hawaiian name of “huluhulu” seemingly refers to the hairy covering of the seed; whilst the Tahitian “vavai” and “ovari” simulate the Fijian “vauvau,” which is merely the reduplicated form of “vau” (the word in many shapes for Hibiscus tiliaceus in Malaya and Polynesia), and is applied by the Fijians to Hibiscus esculentus and to the introduced species of Gossypium.

When in Hawaii I ascertained that neither the seeds of the littoral plant, Gossypium tomentosum, nor those of two cultivated species possessed any fitness for dispersal by the currents, the scraped seeds sinking at once, whilst when covered with the wool they floated only for a few days. Further references to G. tomentosum in Hawaii are given in the index of this volume.

_The Last Stage of the General Dispersal of Plants of the Malayan Era._

We arrive now at the close of the era of the general dispersal of tropical plants, mainly Malayan, over the Pacific, and this brings us down to our own age. The few genera that are still dispersed have no peculiar species in particular groups. The species which often range over all the groups, and retain as a rule their characters in most of them, do not therefore display, except in a few cases, that extreme variation which would give them a place in the ranks of the polymorphous species. The dispersing agencies, in fact, are sufficiently active to check marked variations, and the process of isolation has scarcely begun.

We perceive the reason of this when we look at the nine genera which are taken as samples of this period, viz., Rhus, Osteomeles, Viscum, Plectronia, Boerhaavia, Polygonum, Pipturus, Boehmeria, and Dianella, most of them being known to be dispersed by birds at the present day. Six of the genera possess fruits likely to attract frugivorous birds; whilst one of them, Boerhaavia, has sticky fruits that would be apt to adhere to plumage. Actual observations in the cases of Rhus, Viscum, and Plectronia establish the fact of their dispersal by fruit-eating birds; and there is no difficulty in postulating the same agency for Osteomeles, Pipturus, and Dianella. A method by which Boerhaavia fruits would be transported in the plumage of birds has been observed by Mr. Lister; whilst the nutlets of Polygonum are known to afford food to a variety of birds and to be thus distributed.

In this period the plants all hail from the Asiatic side of the Pacific. Three of the genera, Plectronia, Pipturus, and Dianella, belong almost exclusively to the Old World. Five occur in both the Old and New Worlds, but, as with Rhus, Viscum, Boerhaavia, and Boehmeria, are represented by Old World species in the Pacific, or, as with Polygonum, possess a cosmopolitan species (P. glabrum) ranging over the warm regions of the globe. Even Osteomeles presents no exception to the rule, since the Pacific plant is the only one of its species that is not American.

We have in Polygonum glabrum the only aquatic or semi-aquatic plant widely distributed over the Pacific islands that can lay claim in all groups to be indigenous. It is associated in Hawaii with species of Potamogeton and Naias, aquatic genera that have, however, a limited distribution in Polynesia.

I will now make a few remarks on each genus such as bear on their distribution and on their mode of dispersal in the Pacific.

RHUS (Anacardiaceæ).—The representation of this genus by indigenous species in oceanic islands not only in the Pacific but also in the Atlantic, as in the Bermudas, is of especial interest in connection with dispersal by frugivorous birds, since the drupes are typically dryish and might appear to be not very attractive to birds. There are two Old World species known from the Pacific islands: one being R. simarubæfolia (Gray), distributed over the South Pacific groups from Fiji to Tahiti and hailing from Malaya; the other, R. semialata (Murray), alone recorded from the Hawaiian Group and derived probably from China or Japan. This indication that the groups of the North and South Pacific have derived their species, the first from Temperate Asia and the second from Tropical Asia, is of some interest. In Samoa, according to Reinecke, the fruits of R. simarubæfolia, which are of the size of a pea, form the favourite food of the fruit-pigeons. That birds disperse the seeds of the various Sumachs is familiarly known. In the United States, as we learn from Barrows, Beal, and Weed, crows, woodpeckers, and other birds feed extensively in winter on the fruits of different species of Rhus, including the Poison Ivy (R. toxicodendron). The crows discharge the seeds in pellets after retaining them for about thirty minutes. Some seeds we must infer would pass into the intestines, where they might be retained for ten to twelve hours (see Chapter XXXIII.), which would be long enough, according to Gätke’s views of bird-velocity, to enable them to be transported over a thousand miles of ocean.

OSTEOMELES (Rosaceæ).—One of the most interesting cases of dispersal in recent times over the Pacific islands is that of O. anthyllidifolia. Of the ten known species of the genus, nine are confined to South America; whilst the Pacific species, which is not recorded from America, has been found in Upper Burma, Japan, the Liukiu and Bonin Groups, Hawaii, Pitcairn Island, Mangaia, and Rarotonga. The remarkable distribution of the Pacific plant at once attracts attention. I was very familiar with it in Hawaii, where it forms one of the commonest bushes in open-wooded and thinly vegetated districts at elevations usually ranging from the coast to 3,000 feet. Its small, white, somewhat fleshy fruits would attract birds, and the hard pyrenes would be able to pass unharmed through a bird’s digestive canal. It seems probable that, like Rhus semialata, this plant entered the Pacific Ocean from the north-west, taking the route by Japan and the Bonin Islands, and following the trend of the archipelagoes over Polynesia (see _Bot. Chall. Exped._, Introd. p. 18; _Journ. Linn. Soc. Bot._, vol. 28, 1891, &c.).

VISCUM (Loranthaceæ).—A single species, V. articulatum, which has its home in Southern Asia, is found in most of the Pacific groups, such as Hawaii, Marquesas, Tahiti, Rarotonga, Fiji, &c. The dispersal of the genus by frugivorous birds is well known.

PLECTRONIA (Rubiaceæ).—I have found it more convenient to place this genus here, although there are probably one or two species peculiar to Fiji. This genus of shrubs, which is spread over the warm regions of the Old World, is represented by two widely distributed species in Polynesia, Plectronia odorata (B. and H.) and P. barbata (B. and H.), the first alone extending to Hawaii. I was very familiar with P. odorata in Hawaii and was much interested in its mode of dispersal, since the species has also been found in Fiji, Tahiti, the Marquesas, and Pitcairn Island (Maiden). In one locality, where an old lava-field was partially covered by its bushes then in fruit, the doves were feeding greedily on the drupes, the “stones” of which, as well as the partially digested fruits, were to be seen in quantity in their excrement near a water-hole. The stones are very hard and about a third of an inch (8 mm.) in length, and are exceedingly well suited for transport by frugivorous birds. It was very probably to one of these species of Plectronia that Peale alluded when he wrote of the berries of a species of Canthium forming the principal food, on one of the Paumotu Islands, of Numenius tahitensis, a curlew that has its home in Alaska, migrating south in autumn to Hawaii, Tahiti, and the Paumotu Group (Wilson’s AVES HAWAIIENSES).

BOERHAAVIA (Nyctagineæ).—Two or three Asiatic species of this genus, B. diffusa, B. tetranda, &c., are spread all over the Pacific islands from the Fijis to the Paumotus and northward to Hawaii. Similar or allied species occur on the coral islands of the Indian Ocean, as on Diego Garcia and on Keeling Atoll. Though these plants have often been accidentally spread by man with his cultivated plants, it is probable that sea-birds have regularly aided in their dispersal. The fruits, on account of their small size and their glutinous sticky surfaces, are well suited for transport in a bird’s feathers. Mr. Lister, as quoted by Hedley (from _Proc. Zoolog. Soc._, 1891), made an interesting note in this connection on one of the islands of the Phœnix Group, where he found a fruit of Boerhaavia tetrandra entangled in some of the down that had been preened by a booby (Sula piscatrix) out of its feathers whilst roosting in a clump of Tournefortia trees.

POLYGONUM (Polygonaceæ).—This genus is represented by the cosmopolitan Polygonum glabrum, the only aquatic or semi-aquatic plant that is generally distributed in the Pacific islands. It occurs in fresh-water swamps and beside streams and ponds in Tahiti, Tonga, Fiji, Hawaii, &c., and was gathered by Banks and Solander when Captain Cook first visited Tahiti. That this plant has been distributed by geese, ducks, and waterfowl over the tropics of the globe can scarcely be doubted. In England I have found the nutlets of Polygonum convolvulus, P. persicaria, and P. aviculare in the stomachs of a wild duck and a curlew; and they came frequently under my notice in the crops and intestines of different kinds of partridges and of wood-pigeons. Though most of the fruits were generally injured, a few of them were not uncommonly obtained in a sound condition.

PIPTURUS (Urticaceæ).—This is a genus of small trees and shrubs found in the Mascarene Islands, Malaya, Australia, New Zealand, and throughout Polynesia. Besides P. albidus, which is confined to Hawaii and Tahiti, there are two Malayan species, P. argenteus and P. velutinus, which are widely distributed over the islands of the South Pacific, extending to Tahiti and the Marquesas. The fleshy receptacle and small achenes of the compound fruit of Pipturus give it the appearance of a white immature strawberry, and as such it would be likely to attract frugivorous birds. Plants of this genus are included amongst the numerous plants from the bast of which the natives used to prepare their native cloth or from which they obtained the fibres for their fishing-lines.

BŒHMERIA (Urticaceæ).—There is an Asiatic species widely spread in the South Pacific and another closely-allied species in Hawaii; but I possess no data relating to the dispersal of the genus. The fruits are dry and consist of an achene in a persistent perianth.

DIANELLA (Liliaceæ).—This is a genus of herbs, possessing often pretty blue berries, that extends over tropical Africa, tropical Asia, the Mascarene Islands, Malaya, Australia, and New Zealand, and is found in all the larger Pacific archipelagoes. Of the twelve species named in the _Index Kewensis_ only two belong to America, occurring respectively in Cuba and Venezuela. There are two species in the islands of the tropical Pacific: (_a_) Dianella ensifolia, found in Hawaii and ranging over the Mascarene Islands, India, China, Malaya, and tropical Australia; and (_b_) D. intermedia, recorded from most of the groups of the South Pacific (Fiji, Tonga, Rarotonga, Tahiti), and occurring also in Norfolk Island and New Zealand. These two plants occur in similar stations all over Polynesia, sometimes growing in the grassy plains on the dry side of an island, at other times extending up the thinly wooded mountain slopes and reaching the hill-crests some 2,000 or 3,000 feet above the sea. Their berries would readily attract birds; and their seeds, about one-fifth of an inch (5 mm.) in size in the case of D. ensifolia, could be carried uninjured in the stomach and intestines of a bird.

_Summary._

(1) A later period in the era of the general dispersal of Malayan plants over the Pacific is indicated by the genera that contain species found outside each group as well as species restricted to it.

(2) In this period the extremely variable or polymorphous species plays a conspicuous part, as represented in such genera as Alphitonia, Dodonæa, Metrosideros, Pisonia, and Wikstrœmia.

(3) The first stage is displayed by a solitary widely-ranging species found over most of the Polynesian archipelagoes, and varying independently in every group.

(4) The next stage is shown where the polymorphous species, having done its work of distributing the genus, ceases to wander and settles down and “differentiates” in all the groups; and the genus thus includes both peculiar and widely-ranging species in each group. Most of the genera possessing polymorphous species are in this stage.

(5) The following stage is displayed by those genera like Elæocarpus, Eugenia, and Peperomia, where peculiar species are especially developed in particular groups, and we get subcentres of distribution for the genus, that is to say, small gatherings of peculiar species. A few species, however, still keep up a connection with neighbouring island-groups. Should this be severed we get the type of genus belonging to the earlier period of the Malayan era as described in the preceding chapter, a genus possessing only peculiar species and destined, after ages of further isolation through the failure of the dispersing agencies, to give rise to a new generic type or types.

(6) Frugivorous birds were chiefly active in dispersing these genera over the Pacific. Some of the genera possess seeds or “stones” of such a size that at first sight their transport by frugivorous birds to Hawaii seems improbable; but, as in the case of Elæocarpus, it is shown that this difficulty does not apply to all species of a genus, some of them having much smaller seeds or stones.

(7) The close of the era of the general dispersal of Malayan plants over the Polynesian Islands is indicated by those genera that are represented more or less entirely by widely ranging species. Though such species may vary among the different groups, they rarely take the rank of polymorphous species, the agencies of dispersal being sufficiently active to check marked variations.

(8) Several of the genera of this concluding stage, like Rhus, Viscum, and Plectronia, are known to be dispersed by frugivorous birds, whilst others, like Osteomeles and Dianella, are equally well suited for this mode of dispersal.

(9) Distinct indications are afforded by the genera Rhus, Osteomeles, and Dianella that the Hawaiian Group has been often supplied with its plants directly from the Old World by the Asiatic mainland, whilst the groups of the South Pacific have received different species of the same genus by Malaya and tropical Australia.