There are one or two interesting points relating to the temperate genus Silene, which is represented on these mountains. The four Hawaiian species show a great range in altitude. Thus, whilst S. struthioloides finds its home in Hawaii and Maui at elevations of 5,000 to 9,000 feet, another species (S. lanceolata) thrives equally at elevations of 5,000 or 6,000 feet on the central plateau of Hawaii and at heights only of 300 to 500 feet above the sea. Although I have not yet come upon any direct reference to the mode of dispersal of the small seeds of this genus, there is little doubt that their rough tuberculated surfaces would favour their attachment to plumage. A very significant observation, however, is made by Jens Holmboe in a paper on littoral plants in the interior of Norway. He refers to the occurrence in no small quantity of Silene maritima on the top of “Linnekleppen,” 331 metres high, one of the highest peaks of Smaalenene, and distant about 29 kilometres from the nearest coast (Strandplanter i det indre af Norge, “Naturen,” Bergen, 1899). Sernander (p. 405), commenting on this observation, remarks that since bare hill-tops are frequented by birds, such an agency in this instance is not impossible.
I will conclude these remarks on the non-endemic Hawaiian mountain genera possessing only peculiar species, with a few observations on the genus Vaccinium in the Pacific. This genus is known to be distributed over the northern hemisphere and to occur on the uplands of tropical mountains, as, for instance, on the summits of the Java mountains and on the high levels of the Equatorial Andes at altitudes even of 15,000 to 16,000 feet. There are apparently only some four or five species known from the Pacific islands, from Hawaii, the Marquesas, Tahiti, Rarotonga, Samoa, and the New Hebrides, and it would almost seem that these can be reduced to one or two species. Although not yet recorded from Fiji, the probability of the genus being represented on some of the mountains is pointed out by Seemann. Of these Pacific forms a single species, V. cereum, is spread over the East Polynesian region including the Marquesas, Tahiti, and Rarotonga; and, according to Hillebrand, V. reticulatum, one of the two endemic Hawaiian species, is nearly related to it. Even the New Hebrides species (V. macgillivrayi) resembles it, according to Seemann, in general appearance. That there has been a single Pacific polymorphous species is, as shown below, not impossible; but Reinecke, in describing in 1898 the Samoan species, V. antipodum, was under the impression that it was the only species known from the southern hemisphere, and says nothing of its affinity to other Pacific plants.
A few words on the station and habit of Vaccinium in the Pacific islands may be here of interest. In Hawaii there are, according to Hillebrand, two species, a high-level form, V. reticulatum, occurring at elevations of 4,000 to 8,000 feet, and a low-level form, V. penduliflorum, ranging between 1,000 and 4,000 feet. I may, however, remark that the last species occasionally came under my notice at elevations of 6,000 to 7,000 feet. This species exhibits much variation, and Gray, Wawra, and other botanists have evidently not been always able to distinguish between the two species in their varying forms. It is not only distinguished from the high-level species by its lower station, but also by its epiphytic habit, a circumstance that, as pointed out below, may explain some of the differences, since such a habit is bound up with the difference in station. It seems, therefore, safer to regard them as station forms of one species which is closely allied to V. cereum, the species of the South Pacific, an inference which, if well founded, would make highly probable the view that there has been a single polymorphous Pacific species.... In Tahiti, as we learn from Nadeaud, V. cereum occurs on the mountain-tops at altitudes exceeding 800 metres (2,600 feet). In Rarotonga, according to Cheeseman, it is found on the summits of most of the higher hills extending almost to the summit of the island, 2,250 feet above the sea. The Samoan species, V. antipodum of Reinecke, which that botanist considers as probably one with V. whitmei, a Polynesian (Samoa?) species originally described by Baron F. von Müller, grows in the central mountains of Savaii at an elevation of 1,500 metres (4,920 feet).
These Pacific species of Vaccinium, as on tropical mountains of the continents, occasionally assume an epiphytic habit, and it is here, as above observed, that lies one of the distinctions between the Hawaiian species. V. penduliflorum, the low-level form, occurs typically in the forests, where, according to Hillebrand, it grows on the trunks of old trees. The trees, however, may be quite in their prime, and I have observed it growing in the fork of the trunk of an Olapa tree (Cheirodendron gaudichaudii). It is in this connection of significance to notice that a variety found in open glades and on grassy slopes is described by Hillebrand as terrestrial in habit. The other high-level form, V. reticulatum, grows gregariously on open ground, and is typically terrestrial in its habit. The Samoan species, as we learn from Reinecke, grows on trees, as on the branches of Gardenia. The epiphytic habit of species of Vaccinium is especially discussed by Schimper in the case of plants growing on the Java mountains. He there shows (Plant-Geography, i. 14) that species which are epiphytes in the virgin forest become terrestrial plants in the treeless alpine region. This interchange of station, which is exhibited by several other plants, including orchids and ferns, is connected with their xerophilous characteristics, and is given by Schimper as an example of the interchange of physiologically dry habitats.
Of the mode of dispersal of Vaccinium by frugivorous birds, much has been written and much will be familiar to my readers. The berries of V. reticulatum are known to be the principal food of the Hawaiian mountain-goose. But probably birds of the grouse family have been the chief agents in distributing the genus over the continents. I have frequently found the fruits in the stomachs of the Black Cock (Tetrao tetrix), the Scotch Grouse (Lagopus scoticus), and the Capercailzie (Tetrao urogallus); but the same story comes from all over the northern hemisphere. The Willow Grouse (Lagopus albus), which travels round the globe, is known to feed on them. Hesselman in Sweden and Ekstam in Nova Zembla have especially investigated the dispersal of Vaccinium by Tetrao tetrix and Lagopus (see Sernander, pp. 6, 226); and according to Mr. Douglas and others the different species of Tetrao that frequent the subalpine regions of the Rocky Mountains and the uplands of Columbia and North California subsist on Vaccinium fruits. This family is not now represented in the Hawaiian avifauna; but it is noteworthy, as indicated by the differentiation of the Pacific species of Vaccinium, that dispersal of the genus is there almost suspended except within the region of Eastern Polynesia. It is probable that numerous other birds, except the Hawaiian goose, aided the original dispersal.
The Mountain Genera with both Endemic and Non-endemic Species.—I pass on now to consider those Hawaiian mountain genera that possess species some of which are confined to the group, whilst others occur in regions outside the islands. They are not many, as may be seen from the table before given, and but few of them are entirely restricted to the high levels, a range in altitude that may be frequently associated with great lateral extension of the genus over different latitudes. Here the agents of dispersal have through some species in each genus preserved a connection with the outer world, though it may be restricted to the limits of the Pacific islands.
Cyathodes tameiameiæ, an Epacridaceous species found also in the uplands of Tahiti, occurs, according to Hillebrand, on all the Hawaiian Islands, from 1,800 feet up to the limit of vegetation 10,000 feet and over above the sea. I found it, however, at even lower levels. On the Puna coast of Hawaii, associated with Metrosideros polymorpha, Osteomeles anthyllidifolia, and other inland plants, it descends on the surface of ancient lava-flows to the coast wherever the bolder spurs reach the sea-border. The other species, C. imbricata, is more exclusively confined to the greater altitudes. It is endemic, and may possibly be a station form of the other species.
The six species of Lysimachia are found at different elevations, one near the sea-shore, others at altitudes of 2,000 to 3,000 feet, and others again at elevations of 6,000 feet. Chenopodium sandwicheum occurs at all elevations from near the coast to the high inland plains of Hawaii and to the upper slopes of Mauna Kea, that is to say, up to altitudes of 6,000 or 7,000 feet. Hillebrand observes that it is a low decumbent plant at the coast, and may become arborescent with a height of 12 to 15 feet in the upper forests of Mauna Kea.
The species of Santalum (sandal-wood trees) also display great vertical range in these islands. Though S. freycinetianum, which is also a Tahitian species, is most at home in the forests 2,000 to 4,000 feet above the sea, it has, as Hillebrand informs us, a dwarfed form that extends far up the mountain slopes of Mauna Loa and Hualalai to elevations of 7,000 or 8,000 feet, and another dwarfed shrubby variety that grows only near the sea-shore. Another species, S. haleakalæ, occurs as a tall shrub on Haleakala at elevations of 8,000 to 10,000 feet. Among the sedges, most of those of the genera Carex and Rhynchospora are found at altitudes of between 3,000 and 7,000 feet, and two grasses of the genus Deyeuxia occur at elevations of 6,000 to 8,000 feet.
Amongst these Hawaiian mountain genera with both endemic and non-endemic species there are no plants possessing fruits which from their size could be with difficulty regarded as dispersed by birds. The mode of dispersal of these plants is in some cases indeed not far to seek. Thus in the stomach of an Hawaiian goose (Bernicla sandwicensis), shot by my companion Dr. Krämer on the slopes of Mauna Loa, I found a number of the “stones” of Cyathodes tameiameiæ, the plant being abundant in fruit in the immediate vicinity. It is highly probable that the seeds of Santalum have been carried over the Pacific by frugivorous birds. We learn from Dr. Brandis that Santalum album in India is mainly spread through the agency of birds (Bot. Chall. Exped., iii. 13). The drupes of the Pacific species, S. freycinetianum, that occurs alike in Hawaii, the Marquesas, and Tahiti (Drake del Castillo), measure about half an inch. There can be little doubt that with this tree, as with the species of Cyathodes above mentioned, which also links together Tahiti and Hawaii, there has been up to recent times an interchange by means of frugivorous birds between these two regions, some 2,000 miles apart.