It has been already observed that this is as a rule but slight, and that in the great majority of cases the effect of prolonged drying for many months, or even for years, is at the most to give a seed or fruit originally non-buoyant a floating power of a few days’ duration. This is a subject to which I have paid especial attention in my experiments, since, of course, much depends on it in the way of dispersal by currents. It is obvious that a seed or fruit possessing impermeable coverings at the time of its separation from the parent can scarcely be compared with one where the coverings only attain their water-proof capacity by drying. Most gardeners know that seeds which dry easily take up moisture easily, and the principle applies in a varying degree to the great majority of seeds and fruits.

Darwin was inclined to attach importance to adventitious buoyancy acquired by drying; and in the Origin of Species he refers to instances offered by the fruits of the Hazel (Corylus), the Asparagus, and Heliosciadium. In Note 48 I have referred to the cases of the Oak and the Hazel; and, indeed, we have only to examine the beach-drift in various parts of the world, and to look at their respective stations, to learn that this is not an effective mode of dispersal. Buoyancy of seed or fruit is only one of many other qualities that is concerned with distribution by currents. Nature does not act in this way in seed-distribution, and there can be little doubt that the author of the Origin of Species would have been the first to abandon this view, if his researches had been continued. It should be especially noted that plants of the sea-beach, where the floating power happens to be nil, or limited only to a week or two, would have derived great advantage from the drying of their seeds or fruits if it was really effective in aiding dispersal by currents. However, with plants like Cakile maritima, Eryngium maritimum, Glaucium luteum, &c., the effect of drying is very small.

NOTE 11 (page 25)
 
The Effect of Sea-water Immersion on the Germinating Capacity of Seeds and Seed-vessels

Berkeley, Darwin, Martins, and others, long ago established the capacity of seeds to germinate after prolonged immersion in sea-water. The reader will find a resumé of their results in the appendix to Mr Hemsley’s volume on the Botany of the Challenger Expedition. The subject is well illustrated in the original papers of those authors, and in my later papers on the flora of Keeling Atoll, and on the seed-drift of the Thames.

I may here remark that the earlier observers often pay more attention to the retention of the germinating capacity after sea-water immersion than to the degree of buoyancy. For this reason I have not been able to make great use of the buoyancy results of Martins, since he frequently does not distinguish between temporary and long-sustained buoyancy, an objection also pointed out by Thuret and Hemsley.

NOTE 12 (page 27)
 
The Buoyancy of the Fruits of Galium aparine

Norman and Sernander (see p. 172) attribute considerable buoyancy to these fruits on account of the hollow cavity in each. I used to find them in England in floating river-drift in autumn; and Norman observed them on the Scandinavian beaches. They do not, however, float long, as the cavity is open; and in two sets of my experiments they sank within a few days.

NOTE 13 (page 29)
 
The Buoyancy of the Seeds of Convolvulus sepium

This plant seeded freely in 1893 in the Lower Thames Valley, as at Molesey. I kept some of the seeds afloat for thirty-three months, of which the first nine months were spent in sea-water and the rest in fresh-water. One seed, at the end of the period, germinated healthily in the fresh-water.

NOTE 14 (page 26)
 
Other Long Flotation Experiments

Whilst keeping my collections of Thames seed-drift in water from year to year, I obtained a number of records of long “flotations.” Thus in several cases, as with Bidens cernua and different species of Carex, germination of the floating fruit took place in the water after a period of two years. The same is also true of the seeds of Iris pseudacorus and of the drupes of Sparganium ramosum. The last-named remained afloat in the vessels, with the seed still sound, after four years; and the fruits of Carex paludosa germinated afloat after three years in water. Many drift fruits and seeds did not germinate freely in the vessels until the second spring, that is, after a lapse of eighteen months; and in those cases where the experiments were still further prolonged, a few germinated in the vessels in the third and sometimes even in the fourth year.

NOTE 15 (pages 33, 280)
 
The Occurrence Inland of Silene maritima

Prof. Schimper appeared to be in doubt as to the inclusion of this littoral plant amongst those found in elevated mountain districts. However, an interesting note on the occurrence of this plant on the summit of one of the inland Norwegian mountains is given by Sernander (p. 405), and is referred to by me on page 280 of this work.

NOTE 16 (page 34)
 
The Buoyancy of the Seeds or Fruits of the British Beach-plants that also occur Inland

My experiments in the case of Armeria vulgaris, Artemisia, Cochlearia officinalis, Plantago, the maritime forms of Spergularia rubra with and without winged seeds, and Silene maritima disclose little or no floating capacity even after prolonged drying. Thuret obtained similar results for the Spergularia. It is unlikely that other plants of the group possess any floating power worth speaking of. As indicated in Note 71, the fruits of Raphanus maritimus float only for 7 to 10 days.

Nature disperses the fruits of Armeria vulgaris inclosed in the persistent calyx; but in this condition they float only for 2 to 4 days in sea-water, and the buoyancy of the capsule and seed is still more limited. They are sufficiently light to be blown some distance by strong winds, and the stiff hairs would cause them to adhere to a bird’s plumage in the case of gulls nesting where the plants grow.

Reference to Matricaria inodora is made under Note 18.

NOTE 17 (page 35)
 
The Buoyancy of the Seeds or Fruits of the Group of British Littoral Plants that frequent Salt Marshes and Muddy Shores

Aster tripolium. The achenes, with or without the pappus, sink in fresh and salt water in a day or two even after a year’s drying.

The small seeds, or the seed-like nucules as in Suæda, have but little floating power even after prolonged drying.

Salicornia herbacea. Would be dispersed probably by floating portions of the plant, which, however, soon break down and the liberated seeds sink. The floating seedling thrives in sea-water and could be carried great distances (see Note 19).

Salsola kali. I experimented on this plant, both on the coast of Devonshire and in Chile, with the same results in both localities whether in the fresh state or after drying for weeks. The fruit sinks, but when the plant dries the fruit is often detached inclosed in the perianth, and floats in that condition in sea-water for a few days. Portions of the plant of various sizes bearing mature fruits all sank within ten days. It would seem at first sight, from the observations of Prof. Martins, that the fruits float for several weeks; but his experiments were mainly directed to testing the powers of germination after sea-water immersion; and it is often not at all clear whether flotation is implied or even to be correctly inferred. There is a slight suspicion of germination on the plant. Sea-birds doubtless aid in the dispersion of this plant; the dry crisp portions of the plant carrying fruits catch readily in one’s clothes on account of the prickly-pointed leaves.

Scirpus maritimus. The fresh fruits float a few weeks in sea-water in most cases, but 10 per cent. remain afloat after two months. After drying for some months 30 per cent. remain floating after two months’ immersion.

The fruits float a few days or a week. Drying somewhat increases the buoyancy. Sir W. Buller in New Zealand found in the gullet of Anas superciliosa, the Grey Duck, numbers of the fruits of Triglochin triandrum.

NOTE 18 (page 35)
 
The Buoyancy of the Seeds or Fruits of the British Littoral Plants that are confined to the Beach

Arenaria (Honckeneya) peploides. The seeds float for many months in sea-water unharmed, 75 per cent. floating after a year. They never germinate in sea-water; but on being transferred to fresh water after many months in sea-water they germinate healthily in a few days. These seeds only float a few days in fresh water, all sinking within 10 days, and even after a year’s drying they sink in a week or two. Precisely the same results were produced in my experiments in 1892 on Cornish seeds, and in 1904 on Devonshire seeds. In the great contrast between their floating capacity in sea-water and in fresh water the seeds of this plant defy the general rule that seeds that float a long time in sea-water float also a long time in fresh-water. According also to Sernander the seeds float a long time in the sea. He says that the capsules float, but since they ultimately dehisce this could scarcely be efficacious in dispersal. Floating portions of the plant also aid in its dispersal, according to the same authority (p. 174). The plant forms great extended masses on the pebbly shores of Spitzbergen (Ekstam, p. 28).

Beta maritima. Thuret found that the dried fruits of this plant floated only two or three days in sea-water; whilst in my sea-water experiments the freshly gathered fruits floated only one or two days. Sernander speaks of them as fitted for dispersal from shore to shore; but this could only be to a limited extent. Martins and Thuret established by experiment the capacity of the germination of seeds of other species of Beta after long immersion in sea-water; and the first seems to imply that those of Beta vulgaris float for many weeks; but I am inclined to think an error lies here.

Cakile maritima. The fruits, even after long drying, float, as a rule, only a week and sink within ten days, the same results being afforded in my sea-water experiments in 1893 on fruits from Cornwall, and in 1904 on fruits from Devonshire. The fruits are common in the stranded drift on the north coast of Devonshire and may often be seen germinating there. They are also frequent in the beach drift of the Scandinavian coasts (Sernander, p. 156).

Crambe maritima. The fruits were kept floating by Sernander more than 13 days (p. 165). Martins implies that they floated for 45 days. Darwin says that they germinated after 37 days’ immersion in sea-water, but does not specify that they floated all the time.

Crithmum maritimum. The ripe fruits readily separate into the two carpels, which are very buoyant and float in sea-water for months. In my experiments, 95 per cent. remained afloat after 10 months. It is remarkable that whilst in sea-water the spongy covering of the carpels retains its vitality, in fresh-water it becomes sickly and decays and the carpels lose their floating power, so that they float weeks instead of months as in the sea-water. The carpels are extremely light, being washed up in the spray and blown up by the wind amongst the lightest of the stranded drift of the Devonshire beaches. In a moderate gale they are often blown off the beach and up the cliff-faces.

Convolvulus soldanella. From 40 to 50 per cent. of the seeds float after six months in sea-water, and about 30 per cent. float after eighteen months, retaining up to the end their germinating capacity. Sernander implies that the plant is not found on the Scandinavian coast to the north of Nissum Fjord in Denmark. It is known, however, to occur in the south of Scotland. (I am indebted to Mr. Millett for his extremely kind assistance in experimenting on this plant about ten years since.)

Eryngium maritimum. The fruits float in sea-water, as a rule, only 3 or 4 days and all sink within a week. After drying for three months, the floating period is only increased by a day or two. Though not at all suited for transport for any distance by the currents, the carpels, on account of their long prickly calyx teeth, would readily become entangled in a bird’s plumage, and doubtless they are dispersed usually in that fashion.

Euphorbia paralias. The seeds float a long time unharmed in the sea. In my experiments at least 90 per cent. remained afloat after six weeks in sea-water. On account of their small size they are liable to be overlooked in beach drift; but they are to be found stranded on the sands of our southern coasts, and they came under my notice in abundance in the seed-drift of the Sicilian beaches.

Glaucium luteum.—The seeds have no proper buoyancy even after prolonged drying. On account of their oiliness they will float at first on still water; but they can be made to sink at once or in a day by dropping water upon them. The mode of dispersal is problematical.

Lathyrus maritimus.—The seeds are evidently able to float a long time. They were, according to Sernander (p. 178), found in quantities by J. Schmidt cast up on some sand-islets near Falster in Denmark; and the plant is regarded by Norman as distributed over the coasts of Arctic Norway through the agency of the currents. They have, as observed by Schmidt, considerable floating powers. Some small leguminous seeds, seemingly of this species, which I found in the beach drift of Woollacombe Sands, Devonshire, floated uninjured for many weeks in sea-water.

Matricaria maritima, maritime variety of M. inodora. The fruits floated in my experiments unharmed after eight months in sea-water. In an experiment made some years since on the fruits of the inland form I noted that they had little or no buoyancy; but it is necessary to repeat the observation. Sernander (p. 181) supports Norman’s view that these plants are spread by the currents in Arctic Norway. The fruits occur in the Baltic sea-drift and also in fresh-water drift. M. inodora is found on sandy beaches in Nova Zembla. I am inclined to regard the maritime form from the dispersal standpoint as a distinct species.

Polygonum maritimum.—I have made observations on this plant in Devonshire, the Lipari Islands, and the coast of Chile. As in the case of several other species of Polygonum tested by me the fruits have little or no buoyancy, but inclosed in the perianth they float three or four days. The entire plant floats; but portions placed in sea-water sank within five or six days. Shore-birds can alone explain the wide distribution of this species.

The structural characters of some of these fruits or seeds are in their relation to buoyancy discussed on page 115. It may be here observed that the valuable results obtained by Prof. Martins in testing the germinating capacity of the fruits and seeds of several of the shore-plants above mentioned, after long immersion in sea-water, are at times not to be depended on for the flotation indications, the persistence of the seed’s vitality being the special purpose of his research. His negative results as regards germination are not, however, always conclusive, since the period employed from April to June was quite insufficient. In many of my experiments seeds after long flotation in sea-water did not germinate for a year or more afterwards. If his investigation had been extended, the opinion that the Ranunculaceæ, the Malvaceæ, and the Convolvulaceæ are apparently least able to resist the action of sea-water would never have been formed. A very large amount of evidence now shows that most seeds or fruits that are at all well protected will germinate after long immersion in sea-water. But all experiments must be well safeguarded and extended over a year or two. The necessity of this was long since shown by Thuret. By employing double sets of seeds he ascertained that in a third of the species germination failed not only in the case of the seeds immersed in sea-water, but also in those that had not been placed in sea-water at all. Future investigators may, however, regard the buoyant qualities of seeds or fruits with their associated structural characters as offering now the true line of research. Observers beginning with Berkeley and Darwin down to the present time have quite established the fact that seeds as a rule germinate freely after long sea-water immersion.

NOTE 19 (page 35)
 
On Germination in Sea-water

During my experiments on the buoyancy of about 270 British plants, about a fourth of them (including most of those with buoyant seeds or fruits) were subjected to prolonged immersion in sea-water from periods varying from six to thirty-three months. If we except plants like Aster tripolium, Salicornia herbacea, Triglochin maritimum, &c., that live normally in salt marshes, or on the muddy banks of estuaries, only one of the whole number, namely, Ranunculus sceleratus, displayed the capacity of germination in sea-water. Amongst the plants that failed may be mentioned the following that are confined to the sea-beach—Arenaria peploides, Cakile maritima, Convolvulus soldanella, Eryngium maritimum, Euphorbia paralias, Glaucium luteum, and we may here include Crithmum maritimum of the rocky coasts. Of the beach-plants that also grow inland, Silene maritima and Spergularia rubra (excepting the form found on muddy coast flats) likewise failed. Amongst the plants of miscellaneous inland stations that failed were Atriplex patula, Bidens cernua, B. tripartita, Calla palustris, several species of Carex both from dry and wet situations, Convolvulus arvensis, C. sepium, Hydrocotyle vulgaris, Iris pseudacorus, several species of Juncus, Lycopus europæus, Mentha aquatica, Ranunculus repens, Rhinanthus crista galli, several species of Rumex, Scutellaria galericulata, Sparganium ramosum, &c.

In nearly all the plants that failed to germinate in sea-water the capacity of readily germinating in fresh water was displayed. The restraining power of immersion in sea-water was illustrated over and over again in my experiments. During the course of an experiment seeds removed from the sea-water vessel and placed directly in a vessel of fresh water kept beside the other germinated in a few days, whilst those left in the sea-water never germinated, though often kept there for months after. It was also noticeable that a previous sea-water immersion favoured early germination in fresh water. It may be added that most of the experiments were on floating seeds and seedvessels, though germination also occurred in the sunken state.

It was ascertained in the exceptional case of Ranunculus sceleratus, that although germination took place in sea-water, it was only after a prolonged soaking of months had prepared the way. Of a number of its seed-like fruits placed in fresh water and in sea-water in April and kept under the same conditions, those in fresh water germinated freely in a week or two, whilst those in sea-water did not begin to germinate until the following October. Whilst the floating seedlings produced by germination in fresh water grew vigorously and developed roots, those resulting from germination in sea-water and left in the vessel only attained a length of four millimetres in two months, developed no roots, and showed only the first leaf. The sea-water seedlings were pale green, and in their stout fleshy appearance contrasted greatly with the slender fresh-water seedlings.

With regard to the germination in sea-water of the plants of the salt marsh and of the mud-flats of estuaries, the following observations may be made. With Aster tripolium the seeds germinate readily in sea-water even when its density is raised by evaporation to 1·040; and I think that by a carefully graduated series of experiments they could be induced to germinate in brine. The seeds of Salicornia herbacea germinate in sea-water more readily than in fresh water; and the sea-water seedling is much the more vigorous and healthy of the two. I kept the floating seedlings in sea-water for about ten weeks from the date of germination, when they had developed the second joint and were throwing out rootlets. After that, unless placed in salt-mud, they became sickly and died. The floating seedling can evidently disperse the species. I found with Spergularia marina, the maritime form of S. rubra, that seeds of the plants growing on a sandy beach did not germinate in sea-water, only those from plants growing on muddy coast-flats doing so. But the sea-water seedlings, unlike those of Salicornia herbacea, but like those of Ranunculus sceleratus, when left in sea-water did not thrive. The seeds of Triglochin maritimum, as well as those of T. palustre, behave very similarly in sea-water, germinating readily, the liberated seedlings thriving afloat and producing the plumule. The ultimate test of the capacity for germinating in sea-water seems to lie in the behaviour of the seedling when left in the sea-water. Unless it belongs to a characteristic plant of the salt marsh or of the estuary, like Salicornia, it makes but little attempt at growth whilst afloat in sea-water, showing no rootlets, though at times developing the plumule.

The germination of seeds in sea-water also attracted the notice of Darwin; but his results in some respects are scarcely those I should have looked for (Gardener’s Chronicle, May, 1855, and Journ. Linn. Soc., vol. i., p. 130, 1857). Out of the seeds of 87 plants placed in sea-water to test their capacity of germination when afterwards planted, in three cases, those of Tussilago farfara, Convolvulus tricolor, and the garden Orache (Atriplex), the seeds germinated under the water, the freed seedlings, as with the two first named plants, living in the sea-water for some time after. Darwin was evidently himself surprised at these results, and I am quite unable to understand them. In England and in the tropics I have carried on prolonged sea-water experiments on the seeds of at least fifteen species of Convolvulus and Ipomœa (including the beach plants C. soldanella and I. pes capræ) and have never obtained such a result. The seeds will nearly always germinate well in fresh water; but in sea-water the process begins, as indicated by the swollen seed, and then aborts, the embryo dying (see page 83). The seeds of Atriplex patula, though a long time in sea-water in my experiments, made no attempt to germinate there. Neither Prof. Martins, who experimented upon the effects of sea-water immersion on the seeds of nearly 100 plants, including many coast species, nor M. Thuret, who experimented in sea-water on the seeds of 251 plants, the experiments being in some cases prolonged for more than a year, make any reference, as far as I could gather from their writings, to any cases of germination in sea-water. Darwin’s results, however, are always significant in matters of dispersal; and perhaps one of my readers will be able to experiment again on his three plants.

When in Hawaii, I made some observations on the germination of Batis maritima in sea-water, a plan with which I was also familiar in its home in the salt-water pools of the coast of Peru. The mature fruits, on being freed from the parent plant in sea-water, float away, and in from one to two weeks they break down from decay, setting free the seeds. The seeds float in sea-water indefinitely, their buoyancy only terminating with their germination, the first seeds germinating afloat about six weeks after the breaking down of the fruit, whilst the rest continue to float in the sea-water during the next three months, some of them germinating at intervals, and all of them doing so eventually. Strange to say, although the seedlings remained healthy whilst afloat in the sea-water, they made no effort either to separate the cotyledons or to produce a plumule.

Since they occupy the “talasinga” districts described in the following note, these shore plants would be expected to extend as high as those districts extend, namely, to about 1,500 feet above the sea. This indeed represents their limit excepting in one instance; but many fall considerably short of this elevation.

• Canavalia obtusifolia, variety, 700 feet, rare.
• Cassytha filiformis, 950 feet.
• Cerbera Odollam, 1,200 feet: 2,600 feet in one exceptional case on the slopes of Mbatini.
• Colubrina asiatica, 400 feet.
• Cycas circinalis, 1,100 feet.
• Derris uliginosa, 1,000 feet, rare.
• Ipomœa pes capræ, 1,300 feet.
• Morinda citrifolia, 700 feet.
• Scævola Kœnigii, not common inland, and rarely over 100 feet above the sea; but it may occur miles from the beach, as near Vatu Levoni, where a few stunted plants were growing five miles from the coast.
• Vitex trifolia, 1,300 feet, usually more or less unifoliolate and procumbent.

Unless otherwise stated all the plants above named are common inland, as also are Premna tahitensis, Tacca pinnatifida, Tephrosia piscatoria, Hibiscus tiliaceus, &c.; but I have made no note of Thespesia populnea occurring far off the beach.

NOTE 21 (pages 42, 43)
 
On the Dwarfing of Shore Plants when extending Inland into the “Talasinga” Plains in Vanua Levu.

Premna tahitensis, 9 or 10 feet high at the coast, may here be only 3 feet high. Other trees like Morinda citrifolia become also stunted. Cerbera Odollam, a moderate-sized tree at the coast, may in the “talasinga” plains be only 4 to 6 feet high, but it here displays distinct varietal characters. Whilst the shore trees of Cerbera Odollam have broad leaves (length 3 times the breadth) with obtuse points, and short, stout flower-peduncles (1¹⁄₂-2 inches), the inland or “talasinga” species has long lanceolate leaves (length 7 or 8 times the breadth), and long, slender flower peduncles (3 inches). However, intermediate forms are common, the broad-leaved coast tree approaching the inland plant and vice versâ.

Amongst the most conspicuous features of the north and north-west or lee sides of the large islands of Vanua Levu and Viti Levu are the extensive rolling plains that extend from the sea-border for some miles inland to the foot of the mountains. It is to those of the first-named island that the following remarks strictly apply; but no doubt they will serve equally well for those of the other island. In the first volume on the geology of Vanua Levu, reference is frequently made to this subject, and the reader may profitably look at the remarks there made.

Here the mountain-forests more or less abruptly cease, and we have an undulating region of grass, reeds, and ferns dotted over with Casuarinas, Pandanus trees, Cycads, Acacias, and shrubby growths. Though the list of plants characteristic of these plains is not small, they are not, as a rule, numerous in any one locality, and the general appearance is one of aridity. A dry, crumbling soil, often deeply stained by iron-oxide, is plentifully exposed; and blocks of basic volcanic rocks in all stages of disintegration are strewn over the surface in many localities. Rivers, fed by the heavy rainfall of the forested slopes of the mountains, traverse these regions, but, as a rule, receive no tributaries; and the districts have, in fact, well earned the name given to them by the natives of the “talasinga,” or sun-burnt, lands.

The vegetation, though sparse and scanty in comparison with that of the forests, is sufficiently varied when it comes to be more closely examined. In one locality we may have extensive tracts covered with Gleichenia, Pteris, and other ferns of the bracken habit. In another, tall reeds (Eulalia) and grasses cover large areas. Here, more than one species of Tacca (T. pinnatifida and T. maculata) thrive. There, the Turmeric (Curcuma longa) abounds. Trailing over the soil in one place we notice Ipomœa pes capræ, in another the Yaka (Pachyrrhizus trilobus), and in another the procumbent unifoliolate form of Vitex trifolia. Amongst the shrubs and small trees we observe in different localities the Sama (Commersonia echinata), the Mbulei (Alstonia plumosa—one of the rubber plants), Mussænda frondosa, Melastoma denticulatum, and Nelitris vitiensis, the Nunga-nunga. Dodonæa viscosa, found in similar regions in Australia and New Zealand, abounds in places; and here and there may be seen species of Hibbertia, another Australian genus. Fagræa Berteriana, the Mbua tree, grows abundantly in certain districts, as in the Mbua plains, and Gardenias are at times abundant. One or two characteristic beach-plants have been already mentioned, and amongst others particularly frequent in these plains are Cassytha filiformis, Cerbera Odollam, Morinda citrifolia, and Premna tahitensis.

When these talasinga districts approach the forests, patches of wood occur at intervals, and we observe here the Candle-nut Tree (Aleurites moluccana), the Vunga (Metrosideros polymorpha), and the Thau-kuro (Casuarina nodiflora). Such are some of the botanical features of these districts; but the reader will acquire a sufficiently correct general notion of the floral physiognomy of these regions if he bears in mind their most conspicuous characters, those of an undulating region more or less covered with ferns, tall reeds, and grass, and dotted over, either separately or in clumps, with Casuarinas (C. equisetifolia), Screw-pines (Pandanus odoratissimus), Cycads (C. circinalis), and Acacias (A. Richii, &c.).

However, the peculiar vegetation of these plains often ascends the lower slopes of the mountains, reaching to various elevations. In Vanua Levu it often ceases at 900 or 1,000 feet, but it may only reach to 400 or 500 feet, and, on the other hand, not uncommonly it ascends to as much as 1,500 feet, the greatest elevation recorded by me being 1,600-1,700 feet in the Sealevu district. It extends miles inland, and where conditions are suitable it may reach the heart of the island.

Different explanations have been offered of the origin of the peculiar vegetation of the leeward slopes of these islands. It is, however, a phenomenon that is presented over much of the globe by islands lying in the track of regular winds, the weather, or wet, side being densely wooded, whilst the lee, or dry, side is covered with grass, ferns, and similar vegetation. The predisposing cause must be climatic; and although Mr. Horne’s explanation attributing it to the effect of fires and to a faulty system of native cultivation (pp. 80, 132) may be doubtless true in certain localities, the influences at work here must be the same as are at work in other islands and on continental coasts in other parts of the world.

But for all that it is not easy to give a definite explanation even from a meteorological standpoint. Those who are interested in this subject will recall the desert districts of Australia and the dreary sandy wastes of the coast of Northern Chile and Peru; and they will be cautious in venturing on a definite explanation even with such relatively unimportant examples of the same principle as are exhibited by the islands of Fiji. Dr. Seemann, writing of these “talasinga” plains (p. xii), remarks that “their very aspect is proof that rain falls in only limited quantity,” the mountainous backbone of the islands intercepting, as he holds, much of the rainfall. But the subsequent observations of Mr. Holmes, at Delanasau, in the “talasinga” district on the north-west side of Vanua Levu, have shown that there is by no means a small rainfall in this locality, the average rainfall, for instance, for the seven years ending December, 1877, being 113 inches, which must be quite two-thirds or three-fourths of the fall on the weather side of the island (see p. 215); whilst the average number of days on which rain fell was 156. The true cause would seem to lie in the excessive dryness of the air on the lee side of the islands between the rains, and the whole matter may, perhaps, be one rather for the hygrometer than for the rain-gauge. I have no comparative data bearing on this point; but Mr. Holmes, whose observations as here quoted are from Horne’s Year in Fiji, found that the mean relative humidity for 1875 at 1 P.M. was 63, which is certainly very low for the tropics. I may remark that, as far as personal experience goes, the climate on the lee side of Vanua Levu is much more enervating, much less healthy, and the air is far more “drying” than on the side exposed to the trade-wind.

Geological characters, as I found, explained nothing in this connection, the “talasinga” vegetation sometimes occurring on basaltic areas, at other times on the “soapstone” or calcareous mud-stone, and again on coarser tufaceous rocks. In my volume on the geology of Vanua Levu (p. 57), it is pointed out that the extensive disintegration of the basaltic rocks, that are exposed on these plains in places, affords evidence of the great antiquity of these “talasinga” districts in their present unforested condition. The extent to which these rocks have weathered downward is remarkable. In some places they are decomposed to a depth of ten feet and more. The same inference is to be drawn from the occurrence of fragments of limonite, or bog-iron ore, over these plains, marking as they do original swampy tracts that, with a few exceptions, have long since disappeared. Such deposits indicate that these plains have been for ages in the same condition. ... It may be added that, according to Mr. Lister and Mr. Crosby, the features of the “talasinga” plains occur in the Tongan Group on the leeward sides of the islands of Eua and Vavau.

NOTE 23 (page 43)
 
Schimper’s Grouping of the Indo-Malayan Strand-flora

It is divided into four formations—the Mangrove, the Nipa, the Barringtonia, and the Pes-capræ. The two last make up my Beach-formation, the Barringtonia formation comprising the trees, shrubs, &c., immediately lining the beach, and the Pes capræ including the creepers and bushes of the beach itself. In the Pacific islands it is not always easy to preserve this distinction. The Nipa formation corresponds in some respects with my Intermediate or Transition formation, lying as it does between the mangrove-belts and the woods of the interior; but the swamp-palm (Nipa fruticans) that forms it in the mass is not found in Fiji or, indeed, in the Pacific islands, excepting the Solomon and Caroline Groups.

NOTE 24 (page 44)
 
Grouping of some of the Characteristic Plants of the Strand-flora of Fiji

(a) Beach-formation.—Calophyllum inophyllum, Thespesia populnea, Triumfetta procumbens, Carapa moluccensis, Canavalia obtusifolia, Vigna lutea, Pongamia glabra, Sophora tomentosa, Cæsalpinia Bonducella, Acacia laurifolia, Barringtonia speciosa, Terminalia Katappa, Gyrocarpus Jacquini, Pemphis acidula, Morinda citrifolia, Guettarda speciosa, Wedelia biflora, Scævola Kœnigii, Cordia subcordata, Tournefortia argentea, Ipomœa pes capræ, Cassytha filiformis, Hernandia peltata, Pandanus odoratissimus, &c.

(b) Mangrove-formation.—Carapa obovata, Rhizophora mucronata, Rhizophora mangle, Bruguiera Rheedii, Lumnitzera coccinea, Scirpodendron costatum, &c. (See below.)

(c) Intermediate or Transition-formation.—Hibiscus tiliaceus, Heritiera littoralis, Smythea pacifica, Derris uliginosa, Entada scandens, Barringtonia racemosa, Cerbera Odollam, Clerodendron inerme, Vitex trifolia, Excæcaria Agallocha, &c.

N.B.—It is not possible to draw a definite line between the plants of the mangrove swamp and those of the tracts around. Several of the plants placed in the intermediate formation, such as Heritiera littoralis, Entada scandens, Excæcaria Agallocha, &c., are just as much at home amongst the mangroves. In the same way it is often difficult to distinguish between the Beach and the Intermediate formations, and plants like Cerbera Odollam, Hibiscus tiliaceus, and Vitex trifolia belong equally to both.

NOTE 25 (page 47)
 
The Strand-flora of the Tahitian Region

Drake del Castillo’s Flore de la Polynésie française deals mainly with the Society or Tahitian Islands, but also with the Marquesas, Paumotus, Gambier Islands, and Wallis Island. The last-named, however, lies in Western Polynesia, and is not dealt with in this connection. There is no reason to believe, judging from the general character of the islands and from Cheeseman’s memoir on the Rarotongan flora, that the strand-plants of the islands of the Cook and Austral Groups, which also belong to this region, differ materially from those of the Tahitian islands proper. Rarotonga, however, possesses Entada scandens, not recorded as a growing plant from any other part of East Polynesia, excepting perhaps Mangaia in the same group.

NOTE 26 (page 48)
 
The Fijian Shore-plants not found in Tahiti

Although most of these plants, such as Barringtonia racemosa, Clerodendron inerme, Entada scandens, Excæcaria Agallocha, Heritiera littoralis, Smythea pacifica, &c., have fruits that float for months, and could have reached Tahiti as readily as some of the beach-plants that have successfully established themselves, there are a few like Dalbergia monosperma, Derris uliginosa, and Scirpodendron costatum, the fruits of which only float for weeks, and it is possible that they may have been unable to reach there.

NOTE 27 (page 49)
 
The Intruders into the Beach-flora from the Inland Plants of Tahiti

Drake del Castillo mentions several, such as species of Boerhaavia, that could only be occasional intruders; but it is noteworthy that Gardenia tahitensis appears to be a genuine recruit from inland. The xerophilous habit of the Pacific Gardenias and their station, usually near the coast, however, would render this possible.

NOTE 28 (page 52)
 
The Littoral Plants of the Hawaiian Islands