CHAPTER XIX

THE INLAND PLANTS OF THE PACIFIC ISLANDS

PRELIMINARY COMPARISON OF THE PHYSICAL CONDITIONS OF HAWAII, FIJI, AND TAHITI

Introductory remarks.—The tranquil working of the winds and currents contrasted with the revolutionary influence of the bird.—The Hawaiian, Fijian, and Tahitian groups.—Their surface-areas and elevations.—Their climates.—The mountain climate of Hawaii.—The rainfall of the three groups.—Summary.

INTRODUCTORY REMARKS.

I WILL carry my readers back to that moment when we began to investigate together the composition of the floras of the islands of the tropical Pacific from the standpoint of dispersal. It will be remembered that after collecting all the fruits and seeds of a particular island we placed them in sea-water, and that some nine-tenths of them went to the bottom at once or in a few days. We found, speaking generally, that the buoyant seeds and fruits belonged to coast plants, whilst those at the bottom of the vessel proved to be obtained from inland plants. Since that period we have been occupied in following up the clue supplied by the floating seeds and fruits. In their company we have travelled far beyond the Pacific islands. We have not only seen their fellows in other parts of the tropics, both on the coral atoll and on the continental coast, but we have met their representatives on the beaches of Europe and of temperate South America. We have followed them in their ocean traverses round most of the tropical zone, and on the way we have naturally interested ourselves in the question of the currents. We have weighed these seeds and fruits and have compared their specific weight with that of sea-water. We have cut them up and carefully examined them, and under their guidance we have explored the mangrove-swamps both of Polynesia and of Ecuador, and have penetrated the mysterious _cul de sac_ of vivipary. Having formed our opinion of them, we now bid the subject farewell, and stand once more on the same Pacific beach where, it seems so long ago, our investigations began.

For the seed and fruits lying at the bottom of the sea-water we have to appeal to other agencies than to that of the currents if we wish to inquire into their means of arriving at this island. In imagination we leave the reef-lined shores for the interior, and exchange the exhilarating surroundings of a coral beach, where “the sky is always blue and the wind is always true,” for the arid conditions of an inland plain, or for the humid conditions of the forest, where the rain is incessant and the cloud-cap and mist seemingly eternal. When we look at the motley collection of fruits and seeds obtained in such localities, we are at a loss to know where to take up the clue. After vainly endeavouring to obtain some inspiration as to the manner of commencing the inquiry, we do what all good naturalists in the Pacific islands do from force of habit when they meet with difficulties of any kind—we sit down and light our pipes. Then come a flood of old memories and old trains of thought that came to us years before on some mountain-top or in a shady gorge or on some river-bank, in regions Pacific and non-Pacific, and by degrees our ideas shape themselves and we begin to think the matter over in an orderly fashion.

When the winds first brought the spores of ferns to this Pacific island, the ocean currents brought the seeds and fruits of littoral plants, and the birds transported the seeds and “stones” of various inland species. All three agencies have been working side by side since the earliest stage in its history. Yet it is only in the work of the wind and the current that we find any indication of stability in the floral history of the island. With the work of the bird it has been very different. Since the first bird carried seeds to this locality all else has been turmoil and change. Wave after wave of migrant plants has overrun the interior of the island, and all have left their mark; but the great distributing factor and disturbing agent has always been the bird. Genera have been born and have disappeared, and in their place new genera have arisen. Whole families even have participated in the revolutions of the plant-world, and species have grown rankly in the great confusion. Last of all came man with his cultivated plants and his weeds, introducing new elements of change and discord into the island, and often upsetting the floral economy altogether. The history of man’s most troubled epoch would not be more full of catastrophes and great events than the history of the plants of this Pacific island. Yet through all these changes the winds and currents have been quietly carrying on their work, bringing the same plants to beach and hillside that they did before the age of unrest began.

The monotonous character of an island flora that has been supplied by the winds and currents can be readily imagined. For their variety the floras of the Pacific islands are mainly indebted to the bird, the great disturber of the peace of the plant world. We cannot attach too much importance to the contrast in the results produced by these several agencies in stocking a Pacific island with its plants. On the one hand we have the tranquil working through the ages of the winds and currents. On the other hand there has been the revolutionary influence of the bird. One cannot doubt that many of the species of flowering plants now growing on the beach and many of the ferns on the upper mountain-slopes have witnessed changes within the forest-zone of the island, such as an antediluvian might record if he had lived through the ages to the present time.

Now, what are these changes? How has the bird acted unconsciously such a determining part? These are questions which I will endeavour in some way to answer as one picks one’s path slowly through the various epochs in the plant-history of these islands. We already are fairly well acquainted with the beginnings of a flora either on a coral atoll or on an ordinary tropical beach. What we have yet to learn is the subsequent history of the flora. When Dr. Treub undertook, in 1886, his now celebrated examination of the new flora of Krakatoa after the great eruption, he commenced a series of observations which will no doubt be prolonged into future centuries. Botanists a hundred and two hundred years hence will complete a long chain of observations which will be unique as a record of plant-colonisation; and science is deeply indebted to Prof. Penzig for making, in 1897, the second examination of the new flora. Though deprived of the valuable record that future generations will possess for Krakatoa, we yet have at our disposal in the completed process displayed by many a Pacific island a means of working backward and in a sense completing the history.

In order to attack this problem I have mainly confined myself to the Fijian, Tahitian, and Hawaiian floras, taking the three archipelagoes just named as the centres of the regions in which they occur. These three groups lie near the three angles of the triangular area of the Pacific over which the various archipelagoes are scattered. They are thus geographically well placed for an inquiry into the subject of plant-dispersal over this ocean, and each of their floras has been investigated by botanists of various nationalities—American, Austrian, British, French, German, and Italian. The Fijian area may be regarded as including the adjacent Samoan and Tongan groups, though the individual group or the whole area will always be in this work particularised. In the same way Tahiti will be viewed as usually representative of the larger islands of the surrounding groups of the Cook and Austral Islands and of the Marquesas; and under the designation of the Tahitian area or Tahitian region there will be generally included the Paumotu archipelago.

COMPARISON OF THE AREAS AND ALTITUDES OF HAWAII, FIJI, AND TAHITI.

Since differences in physical conditions have played an important part in plant distribution in these groups—such, for instance, as in determining the development of a mountain flora or in favouring the relative abundance of particular types of plants—it is at first essential to obtain a general idea, in the case of the larger islands of each group, of their size and elevation, and of the more conspicuous differences in their climates.

Hawaii, the largest island of the Hawaiian archipelago, has an area of 4,210 square miles. All the other islands of the group are considerably smaller—Maui, the second in size, having a surface of 760 square miles; Oahu coming next; and after it Kauai, with an area of 590 square miles. The area of Viti Levu, the largest island of the Fijis, is 4,112 square miles, being thus closely similar to that of the island of Hawaii; Vanua Levu, the second in size, is 2,433 square miles in extent; whilst the other important islands of the group are much smaller, Taviuni, the third in size, having an area of 218, and Kandavu an area of 125 square miles. Tahiti, the largest and loftiest island of Eastern Polynesia, has a surface of about 400 square miles; whilst most of the other elevated islands of the groups around are considerably smaller.

In respect of elevation above the sea, there is a great contrast between the islands of these three regions. Taking the Hawaiian Group first, we notice that the three principal mountains of the large island of Hawaii rise in the cases of Mauna Kea and Mauna Loa to between 13,000 and 14,000 feet, and in that of Hualalai to rather over 8,000 feet. Situated between these three mountains there is an extensive tableland or plateau, known as the Cattle Plains, which is elevated between 4,000 and 6,000 feet, and has an area of not less than 200 square miles. At least a third of the whole area of the island exceeds 4,000 feet in altitude. In the eastern portion of Maui the huge mass of Haleakala rises to rather over 10,000 feet; whilst Mount Eeka, in West Maui, rises in bulk to some 6,000 feet. The island of Kauai, which is elevated between 5,000 and 6,000 feet, possesses in its interior an elevated tableland 40 square miles in extent and 4,000 feet in altitude. Oahu attains in Mount Kaala a maximum elevation of 4,000 feet, but 3,000 feet is the limit of the other peaks, and much of the island is low in elevation.

On the other hand, in the two largest islands of Fiji, namely, Viti Levu and Vanua Levu, we find in the first-named only two or three of the highest mountain peaks rising to between 4,000 and 5,000 feet; whilst the highest peak of Vanua Levu reaches only to about 3,500 feet. Amongst the lesser islands, Taviuni just reaches the level of 4,000 feet, and Kandavu, the next in height, about 2,750 feet. The area of the land-surface in this group that is above a level of 4,000 feet is very scanty, and for the botanist a negligible quantity, so that for purposes of comparison the Fijian Islands, as far as elevation is concerned, correspond to the lower levels of the Hawaiian Islands, that is, to the areas below 4,000 feet. The same may be said of the Samoan Islands with the exception of a limited area in the centre of Savaii, where a peak rises to 5,400 feet above the sea.

Coming to the Tahitian region, we find that Tahiti, the most elevated island, attains an extreme height of about 7,300 feet; but from its surface-configuration it is evident that not one-tenth of the area exceeds 5,000 feet; yet since its total extent is about 400 square miles there must be an elevated region of some 30 square miles in amount comparable in some degree with the uplands of Hawaii. The Marquesas, next in order in size and height, attain a maximum elevation of about 4,000 feet; whilst, amongst the Cook and Austral Groups, Rarotonga reaches a height, according to Mr. Cheeseman, of 2,250 feet. Excepting the limited elevated area of the uplands of Tahiti, there is nothing in Eastern Polynesia corresponding to the higher levels of the Hawaiian Islands over 4,000 feet. We formed the same conclusion for Fiji, and I may add that it applies to the whole area of Fiji, Samoa, and Tonga, since the solitary peak of Savaii in the second-named group, which reaches 5,400 feet, alone represents a high-level area. The uplands of Hawaii—that is to say, the elevated region between 4,000 or 5,000 feet and 14,000 feet (strictly speaking 13,800 feet)—are therefore almost unrepresented amongst the Oceanic groups of the South Pacific; and it is only in the peak of Savaii and in the limited high levels of Tahiti that we would expect to find their conditions reproduced. The great effect that this contrast implies in determining differences between the floras of the Hawaiian, Fijian, and Tahitian regions will become apparent as we proceed in this discussion.

COMPARISON OF THE CLIMATES OF HAWAII, FIJI, AND TAHITI.

Before comparing the climatic conditions in the three groups, it may first be remarked that since they lie, roughly speaking, at not very dissimilar distances north and south of the equator a great contrast is not to be expected in so far as they agree in elevation. The mean latitudes do not differ greatly, that of Hawaii being 20° to 21° N., and those of Fiji and Tahiti both about 18° S. The climate of both groups is tempered by the north-east trade in the one region and by the south-east trade in the other. Still there is a difference in the temperature and dryness of the air which noticeably distinguishes Hawaii from Fiji, and to a less extent from Tahiti. The mean temperature of the Hawaiian Islands would be 74° or 75°; whilst that of Tahiti is placed at 76° to 77°, and that of Fiji at 79°. But it is to be observed that to a person residing in Fiji after a residence in Hawaii the climate is perceptibly warmer, more humid, and more enervating. No doubt this is in part connected with the greater dryness of the air in Hawaii, where the average relative humidity at Honolulu is placed at 72 per cent., and it must be much less on the Kona coast on the dry side of the largest island. It is, however, probable that the Hawaiian climate was less dry before the destruction of the forests, and that the contrast with the Fijian climate was then less pronounced.

The great distinguishing feature, however, of the Hawaiian Islands is to be found in their mountain climate. This is not represented in Fiji, but slightly in Samoa, and to a small extent in Tahiti; and I will now refer more particularly to this important subject.

In the uplands of the large island of Hawaii, on the tops of the lofty mountains 10,000 to 14,000 feet above the sea, we have a mean temperature only found far north. Snow lies often on these barren summits in winter, more particularly on Mauna Kea, which thus derives its native name of the White Mountain. The details of my meteorological observations on Mauna Loa will be found in Note 61; and only some of the general results will be referred to here.

The mean temperature for the period of twenty-three days passed by me on the summit of Mauna Loa (13,600 feet) between August 9th and 31st, 1897, was 38·5° F. The mean temperature for a period of twenty days from December 24th, 1840, to January 12th, 1841, during which Commodore Wilkes and his party were making pendulum observations on the summit of the same mountain, was approximately 33·5° (see Note 61). From these results, which are tabulated below, it will be seen that the mean annual temperature would be probably about 36°, which is scarcely comparable with any continental climate, since only a difference of a few degrees is indicated between the mean temperatures of August and of a similar period in mid-winter. I may add that although it was in the summer month of August, water froze inside my tent during twenty out of the twenty-three nights passed on the top. We may, therefore, infer that the temperature falls below the freezing point at night practically throughout the year. It will be seen from the table that the mean annual temperature for the summit of Mauna Loa, as here computed from the observations of Commodore Wilkes and myself, comes very near to that which might be estimated by employing Hann’s tables of variation in temperature with altitude on tropical mountains (see Schimper’s _Plant-Geography_, iv. 691).

WINTER AND SUMMER TEMPERATURES ON THE SUMMIT OF MAUNA LOA (13,600 FEET), IN DEGREES FAHRENHEIT.

+---------+---------------+--------------+-------+--------+--------+------------+ |Observer.| Period. | Mean daily |Lowest.|Highest.|Mean for|Approximate | | | | range. | | |period. |yearly mean.| +---------+---------------+--------------+-------+--------+--------+------------+ |Wilkes |Dec. 24, 1840- |17°-50°=33° | 13° | 55°? | 33·5° | } | | |Jan. 12, 1841 | | | | | } | | | | | | | | } 36° | |Guppy |Aug. 9-31, 1897|23·2-53·8=30·6| 15 | 61·2 | 38·5 | } | +---------+---------------+--------------+-------+--------+--------+------------+

Estimated mean annual temperature of the summit of Mauna Loa, taking that of the coast at 75°, would be 34° if the rate of increase was the same as on Mount Pangerango in Java (1° per 328 feet).

The great daily range of temperature is one of the most striking features of the climate of the summit of Mauna Loa. The extreme recorded by me was 38·7°, whilst Wilkes registered as much as 42°. As on most lofty mountains the dryness of the air, as indicated by the relative humidity, was usually great. The average percentage during my stay between 8 and 9 A.M. was 44, at midday 43, and between 5 and 6 P.M. 56. This may be contrasted with 72, the average for the year at Honolulu. In the tropics the mean for the year in the lower levels often rises to 80 and over; and it can scarcely be doubted that the Hawaiian climate is generally drier than it was before the destruction of the forests. The lowest relative humidity recorded by me on the summit of Mauna Loa was 20 per cent. Junghuhn on the summits of two mountains in Java, 10,500 and 11,500 feet in height, recorded percentages as low as 5 and 13. Further details relating to this subject are given in Note 61. The rainfall on the top of Mauna Loa is probably very slight. During my sojourn rain was noted on six days, but on only two could it be measured, and the total fall could not have amounted to over a third of an inch.

The mean annual temperature of the great forest-zone at the elevations where it displays the greatest luxuriance of growth on the island of Hawaii, that is, between 4,000 and 6,000 feet, would be estimated at 63° and 57° F., if we take the rate of decrease before employed of about three degrees per 1,000 feet. But remembering the heavy rainfall in this region and the usual occurrence of a protecting belt of cloud during the day, this might seem to be too high. According, however, to a table given by Mr. Jared G. Smith in his annual report of the Hawaii Agricultural Experiment Station for 1902, the average temperature at 4,000 feet would be 65°. I cannot help thinking this is excessive as an average for the island. In the latter part of May, 1897, the mean temperature during my sojourn of twelve days at elevations between 6,000 and 6,700 feet around the slopes of Mauna Kea was 51·2°; whilst for eight days in the first part of June in the same region the mean temperature was 58·2° at an altitude of 4,000 to 4,300 feet.

It is possible, as I have pointed out on a later page, to recognise in the different zones of vegetation the floras of a variety of latitudes; and these zones are to a large extent controlled by temperature as well as by other conditions. Thus the Fijian would be amongst familiar vegetation on the lower slopes of Mauna Kea, whilst the Maori would be at home halfway up the mountain-slopes, and the African from the upper forests of Kilima Njaro and Ruwenzori would find in the higher levels much to remind him of his native land.

The upper woods extend usually to 8,000 or 9,000 feet above the sea, and vegetation of a scrubby character occurs as high generally as 10,000 or 11,000 feet. The highest regions present only a barren rocky waste.

THE RAINFALL.

_The Hawaiian Islands._—Although on account of the extensive deforesting of the Hawaiian Islands since their discovery the contrast between this group and that of Fiji is now, as regards rainfall, somewhat emphasised, it is almost certain that in early times the contrast was much less marked. In the lower levels the natives and sandal wood traders in the past, and the agriculturists in the present, have accomplished much in this direction. Between 1,000 and 3,000 feet, whole forests were in my time disappearing under fire and axe for the coffee plantations. Above those levels up to the higher limits of the woods, cattle were destroying the forests in a wholesale fashion; whilst foreign insects were proving themselves almost as great enemies to the vegetation. I remember an enterprising agriculturist explaining to me how he cleared the land of forest around his station. A large tract having been fenced in, the cattle were introduced. After destroying the undergrowth and the young trees, the animals attacked the bark of the trees, and in a year or two, without fire or axe, the land was cleared. The consequence of this unchecked destruction of the forests was in my time becoming only too evident. When I passed through Ookala, on the Hamakua coast, at the end of May, 1897, there was a water famine. Water was sold at a quarter of a dollar a bucket, and the allowance for a family was three oil-cans a week. Stealing water was a crime and punished by the plantation authorities by dismissal or a five-dollar fine.

If we could look back for fifty or sixty years—I am now quoting from the reports of Prof. Koebele and Dr. Stubbs—we should see large forests where we now see barren slopes and plains. Originally forests covered the upland plateaux and mountain slopes of all the islands. Now much of the original forests has been removed, and large areas of naked soils and bare rocks remain. The present forest area, writes Mr. Giffard, the editor of the _Hawaiian Forester_ (August, 1904), is about 20 per cent. of the islands, a small fraction of what it was a hundred years ago. It is, however, very satisfactory to learn that American energy is now combating this evil. Already in the January number of the same journal is to be found a report by Mr. W. L. Hall, of the Bureau of Forestry, on “The Forests of Hawaii”; and now, under the charge of Mr. Jared G. Smith, institutions have been formed and experiment stations have been established for “the intelligent and skilful cultivation of the soil.” Hawaii owes much to the United States Department of Agriculture. May we in England take the cue in the case of our own Crown colonies!

Under these circumstances the comparison of the present rainfall of Hawaii must be carried out with discrimination. But it may be at once observed that to make a contrast in detail between the rainfalls of these three groups is quite beyond the province of this work; and this remark applies also to the other observations on the climatic conditions. I can only treat the subject in an illustrative fashion in connection with the general subject of their floras.

Thanks to Professor Lyons, the Government meteorologist, the rainfall has long been systematically investigated. It may be said to range anywhere between 10 and 300 inches. As in most groups within the trade-wind belts, there is a great contrast in the rainfall between the weather and leeward sides of the islands, which is well exhibited in the large island of Hawaii. Whilst in the Hilo district on the wet side of the island the annual rainfall near the coast is about 120 inches, on the Kona coast of the dry side of the island it may be anything between 20 and 50 inches and it may fall to less than 10. The effect of elevation is, however, evident on both the weather and lee sides of the island. Thus at a height of 1,650 feet in the Hilo district it is as much as 180 inches, and at a greater elevation 210 inches. At a height of about 1,600 feet at Kealakekua, on the dry side of the island the average yearly rainfall, according to the results kindly supplied to me by the Rev. S. H. Davis, was for the six years, 1891-6, 60 inches. On the beach, as he says, it is “very much less,” probably not 30 inches. Dr. Maxwell, in his report on “Irrigation in Hawaii,” mentions a locality in Maui where the rainfall at the sea-shore was 28 inches, and at a height of 2,800 feet up the mountain side as much as 179 inches. In the region of the cloud-belt, which coincides with that of the forest-zone on the slopes of the great mountains of Hawaii and extends up from about 3,000 to 7,000 or 8,000 feet above the sea, the average annual rainfall would probably be rarely under 200 inches, and in some localities it might approach 300 inches. There are some particularly wet mountains, and amongst these may be placed the high table-land of Kauai (4,000 feet) and the flat summit of Mount Eeka (6,000 feet) in West Maui. Here in a region almost of eternal mist we have developed a special bog-flora.

Hillebrand describes the flat top of Mount Eeka as “wrapt in a cloud of mist nearly the whole year.” Whilst descending this mountain I was overtaken by the darkness at a little under 5,000 feet above the sea. Through the night there was a continuous soft rain, or rather a heavy wet mist, and I passed it under conditions suggestive of living in a sponge. Everything was reeking with moisture. The air was saturated with it, and water dripped from every leaf and branch, whilst the ground on which I stood was soft and yielding and soaked with water like a sponge. The surface was cut up by numerous narrow water-channels ten to twenty feet deep and only a couple of feet wide, their very existence almost concealed by ferns, whilst torrents rushed along at the bottom and kept up a strange music through the night. This was the longest night I have ever experienced, as my standing-ground was very limited, and with a water-channel a foot or two away on either side I had to keep on my legs until the dawn.

Above the cloud-belt, at elevations of 10,000 feet and over, the rainfall is evidently very small. I have before remarked that during my stay of twenty-three days (August 9-31) on the summit of Mauna Loa (13,600 feet) the rain did not exceed one-third of an inch in amount. I have by my side the report to the Weather Bureau, compiled by Prof. Lyons, on the rainfall of this large island of Hawaii for the entire month (August, 1897); and it enables one to make a comparison, in some respects unique, of the distribution of the August rainfall on Mauna Loa, from its base to its summit, where it occupies the breadth of the island. Whilst on the east or wet side from the coast up to 1,500 feet amounts ranging from 11 to 15 inches were measured, on the west or dry side between one and two inches were registered at the coast, and 10 inches at Kealakekua, about 1,600 feet above the sea. But the level of maximum precipitation would lie much further up the mountain slopes on either side, probably at an altitude of 4,000 or 5,000 feet, and here the rainfall for the month could not have been less in either case than 20 inches. Above this line of greatest rainfall the amount of atmospheric precipitation would become less and less until beyond the upper forest zone above 10,000 feet to the summit (13,600 feet) the quantity would be very small; and judging from my observations, that covered three-fourths of the month, the rainfall on the top of the mountain for August would not have far exceeded half an inch.

The dry climate of the summits of Mauna Kea and Mauna Loa is reproduced on the tops of the Java mountains and on the summits of the Owen Stanley Range in New Guinea. Sir W. Macgregor found a fine and dry climate on the top of the mountains last named, beyond the limits of the forests, which extend to 12,000 feet above the sea. Below lay the cloud belt, a zone of moss and fog, where at an elevation of 7,000 to 8,000 feet everything was reeking with moisture (_Journ. Roy. Geogr. Soc._ 1890). Observers at the coast often little imagine, when looking at a cloud-concealed mountain peak, that although the cloud-belt from below looks black and lowering and rain is falling heavily in the gloomy forests, there is on the upper side a region of bright sunshine, and that the peak stands out, unseen by them, above a sea of clouds sparkling brilliantly in the sun and dazzling in their whiteness. It will be seen from the table given in Note 61, that during my sojourn on the summit of Mauna Loa the sky was cloudless or almost free from cloud during nearly half the time. The mean cloudiness in the forenoon for twenty-two days was 1·3 and for the afternoon 3·5, whilst the nights were cloudless.

_The Rainfall of Fiji._—The rainfall of Fiji is known to be very large. In illustration I will take Vanua Levu, the second largest island, partly because of my familiar acquaintance with it, and partly because I have at my disposal measurements for both the lee and weather sides of the island—the first dry and characterised by a scanty and peculiar vegetation, the second humid and densely forested. At Davutu, near the sea-level on the weather or wet side of the island, the average yearly fall for a period of sixteen years up to 1898 was 160 inches (these observations were made in the grounds of the manager’s house and I am indebted to Mr. Barratt for allowing me to inspect them). The mountainous backbone of the island, which has an elevation ranging usually from 2,000 to 3,000 feet, is generally in the rain-clouds. During the months I was occupied in examining the geology of these mountains, it was a common experience to be drenched to the skin all day long, and I cannot doubt that the annual rainfall in the higher levels must often reach 300 inches. Those familiar with the “sun-burnt” lands or “talasinga” plains that mainly form the north or lee side of the island, would expect a great difference in rainfall as compared with the south or weather side. There is a marked difference, it is true, but it is far less than we might have looked for. At Delanasau on the north coast, less than a hundred feet above the sea, the mean rainfall for seven years (1871-77), according to the observations of Mr Holmes, was 113 inches, and the range 80 to 159 inches (see Horne’s _Year in Fiji_). In discussing the origin of the arid-looking plains on the north or lee side of the island in Note 22, I have shown that the explanation is to be found not so much in the rainfall as in the dryness of the air as indicated by the relative humidity.

The rainfall varies greatly in and around Vanua Levu, but there is little doubt that by far the greatest bulk of the rain is precipitated on the upper weather slopes of the mountainous backbone of the island. Taviuni, which lies off its weather coast, is probably the wettest among the smaller islands of the group. In 1877, when 80 inches were recorded by Mr. Holmes at Delanasau on the north side of Vanua Levu and 73 inches at Levuka in the island of Ovalau, 251 inches were measured in Taviuni at Ngara Walu 564 feet above the sea; and in 1875 the rainfall recorded at Taviuni was 212 inches, and at Delanasau 126 inches (Horne).

Fortunately, the Fijian islands have not been long enough occupied by the whites to produce much effect on the rainfall through the destruction of the forests. A significant warning, however, has been given in the vicinity of Levuka. The woods of the hills around the town, as we learn from Mr. Horne, were cut down to prevent them from affording shelter to the unfriendly natives of the interior, the result being to reduce the number of rainy days in a few years from 256 to 149 per annum.

_The Tahitian rainfall._—The annual rainfall of the coast districts of Tahiti is placed at about 50 inches (_Encycl. Brit._ vol. 23); but, as is observed by Nadeaud and Drake del Castillo, the rain-clouds gather round the peaks, and the precipitation is much greater in the interior than at the “littoral,” with a corresponding result in a striking difference between the vegetation of the two regions. Probably, therefore, the rainfall for the year on the wooded mountain slopes and at the heads of valleys where the vegetation is most luxuriant would be over 100, and perhaps as much as 150 inches in places. (The annual rainfall in Rarotonga is, according to Cheeseman, about 90 inches.)

It is evident that in the three groups of Hawaii, Fiji, and Tahiti, the rainfall varies greatly with situation and with elevation; but the contrast is much greater in Hawaii than in Fiji. Thus there would be scarcely any place on the lee side of Vanua Levu where the average annual fall would be less than 80 or 90 inches, except perhaps in the Undu Promontory, whilst on the lava-bound coast of the west or lee side of Hawaii, it may be reduced to 20 inches and less. There is no doubt that this was to some extent the case in pre-European times, since Fiji must have possessed for ages, on the northern sides of the larger islands, its arid “talasinga” or “sun-burnt” plains; and in the island of Hawaii there must have always been vast, scantily vegetated lava fields at the sea-border. It is probable, however, that it is in the older islands of the Hawaiian group, those where the volcanic forces have been long extinct, that the rainfall has been chiefly affected by deforestation. Speaking generally, in pre-European times the climatic conditions of the lower levels of the group, that is below 4,000 feet, which are alone comparable with Fiji, were less contrasted with the climatic conditions of the Fijian islands than they are at present. By reason of their great elevation, the Hawaiian islands present a mountain climate not found in Fiji, and scantily represented in Tahiti. It is, therefore, in the flora of the Hawaiian uplands that we should expect to find the great distinguishing feature between that group and Fiji.

_Summary of the Chapter._

(1) Whilst the winds and the currents have been working tranquilly through the ages, bringing always the same vascular cryptogams and shore-plants to the Pacific islands, the bird has ever been a disturbing factor in the inland flora, and changes often of a revolutionary character have taken place from time to time within the forest-zone.

(2) In the discussion of the inland plants of these islands, the Fijian, Tahitian and Hawaiian areas are taken as centres of development and dispersal, and as including the groups around.

(3) On account of the contrast in physical conditions presented by these archipelagoes, differences with which some of the most distinctive features of the floras are to be connected, a comparison of the islands from this standpoint is first necessary.

(4) Since the largest islands of the Fijian and Hawaiian areas are from five to ten times the size of Tahiti, the largest island of the Tahitian region, we would expect to find in the two first-named groups a much more varied flora.

(5) There are three huge mountain-masses in the Hawaiian group which rise to between 10,000 and 14,000 feet, and there is in the aggregate a large area elevated more than 4,000 feet above the sea. These elevated regions are almost unrepresented in the southern groups, the Fijian islands being only comparable with the lower levels of the Hawaiian islands below 4,000 feet, and the same is true of all the groups with the exception of a limited area in Tahiti, where the mountains reach a height of 7,300 feet, and of the solitary peak of Savaii in Samoa, which attains an altitude of 5,400 feet. Thus the conditions for a high-level or mountain flora which exist in Hawaii are not to be found in Fiji, but slightly in Samoa, and to a limited extent in Tahiti.

(6) From their position with regard to the equator and with reference to the trade-winds a great contrast between the climates of these three regions—the Fijian, the Tahitian, and the Hawaiian—is, as far as the islands agree in elevation, not to be expected, and in fact does not exist. The Fijian climate, however, is now warmer and more humid, and the general rainfall is greater than in the case of Hawaii, but it is probable that these differences were much less pronounced before the destruction of the Hawaiian forests, which has been in progress since the discovery of the group.

(7) Anywhere around the coasts of the larger Fijian islands we might expect an annual rainfall of not less than 80 or 100 inches. In the Hawaiian group the rainfall at the coast may be anything between 10 and 100 inches, but is generally less than 50 inches. In Tahiti, at the coast, it is 50 inches. In all cases the rainfall increases greatly with elevation. In the Fijian mountains the rainfall probably varies between 200 and 300 inches. In the Hawaiian forest-zone it would range probably between 100 and 200 inches, though this is probably exceeded in a few localities. In the Tahitian uplands it would doubtless exceed 100 inches and approach 150 inches.

(8) Quite a different climate prevails on the lofty summits of Hawaii 13,000 to 14,000 feet above the sea. Here the snow lies in winter, and the mean annual temperature is only a few degrees above the freezing point, probably about 36° F. The difference between the mean summer and winter temperatures is very small, and does not exceed five or six degrees. Water freezes here during nearly every night of the year. The daily variation of temperature is very large, the average being probably about thirty degrees. Great dryness of the air prevails, the average relative humidity in August, 1897, being about 43 per cent. There is but little rain. The sun shines fiercely, and the sky is usually clear.

(9) All Pacific climates are represented in the Hawaiian mountains, that of Fiji on the lower slopes, that of New Zealand half way up, and that of the Antarctic islands on the summits.

(10) When contrasting the floras of Fiji, Tahiti, and Hawaii, it will be necessary to restrict our comparison in the case of Hawaii to the lower slopes below 4,000 or 5,000 feet; and we should expect the Hawaiian mountain flora to be scantily represented in Tahiti, and scarcely at all in Fiji and Samoa.