(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.
CHAPTER XX
THE EPOCHS IN THE FLORAL HISTORY OF THE PACIFIC ISLANDS
The Age of Ferns
The epochs in the plant-stocking.—The age of ferns and lycopods.—The relative proportion of vascular cryptogams in Hawaii, Fiji, and Tahiti.—The large number of peculiar species in Hawaii.—The mountain ferns of Hawaii.—The origin of peculiar species.—Dr. Hillebrand’s views.—Their origin connected not with greater variety of climate in Hawaii, but with isolation.—Summary.