Luffa insularum
This is regarded as a maritime form of Luffa cylindrica, a plant commonly cultivated throughout the tropics. The South Pacific plant, which occurs also in Australia and Malaya, has been found in New Caledonia, Fiji, Tonga, Rarotonga, and Tahiti. In Fiji it grows chiefly on the “talasinga” plains and in places once under cultivation. I noticed it in one locality climbing over the branches of an Inocarpus tree on the banks of the Rewa. In Rarotonga it is common in the lower regions. It is, according to Nadeaud, fairly frequent on the shore and in the lower valleys of Tahiti, where it was collected by Banks and Solander, the companions of Cook. The Pacific islanders, as far as can be gathered, make little or no use of the plant; and unless it was introduced accidentally with their cultivated plants, they could scarcely have been concerned in its dispersal.
In Fiji I made a special point of investigating the mode of dispersal of this plant. The fruits, which ultimately become dry and fibrous, are to be seen hanging vertically from the plant as it climbs among the branches of a tree. The apical disk usually falls off, and many of the seeds drop out through the hole thus produced; but a few remain entangled in the fibrous material occupying the interior of the fruit. I have noticed such fruits floating down the stream of the Rewa River; but my experiments showed that they do not float more than a week, whether in fresh or salt water. The seeds, however, possess a hard, impervious shell, and are well adapted to withstand unharmed prolonged immersion in the sea. They will evidently float for months. Out of one hundred selected seeds placed in sea-water, sixty were found afloat and sound after two months. The cause of the seed-buoyancy is purely mechanical. Neither the shell nor the kernel has any floating power, the buoyancy arising, as with Convolvulaceous seeds, from the unfilled space in the seed-cavity. When in Fiji, I tested the seeds of the ordinary cultivated tropical form of the plant which had been introduced into a garden from Australia. They all sank in a few days, and on being cut across the seed displayed but little unoccupied space in its cavity. I have no doubt that the Pacific form of this plant has been at times dispersed by the currents, not, however, through the fruits, but through the seeds. It is also quite possible that it may have been introduced by a pre-Polynesian people into the Pacific.
Summary of the Chapter
(1) Man in his distribution over the Pacific islands reproduces, but in a less degree, nearly all the difficulties presented by the plant in its dispersal. In both we have the age of general dispersion followed by a suspension more or less complete of the migrating movements; and in both we have differentiation associated with the isolation.
(2) The Pacific islanders possess two sets of food-plants. In addition to those commonly cultivated in our own time, such as the yam, the taro, the banana, &c., there are a number of food-plants now growing wild, but rarely cultivated, and only used when the others fail. These plants, which include the wild yams, the mountain bananas, Tacca pinnatifida, Pandanus odoratissimus, and several others, are regarded as older than the Polynesians in the Pacific, and as having probably formed the food of a pre-Polynesian race that practised only a rude sort of cultivation.
(3) The weeds of Polynesia also fall into two groups. In the first place there are the aboriginal weeds, of which those found in this region by Captain Cook’s botanists in the latter part of the 18th century are taken as examples. These include species of Urena and Sida, besides Waltheria americana, Oxalis corniculata, Bidens pilosa, and many other weeds. In the second place, there are the numerous weeds that are known to have been introduced by the white man since the voyages of the English and French navigators of Captain Cook’s time.
(4) There is reason to believe that many weeds now cosmopolitan in the tropics had obtained their present distribution in America and in the Old World before the Polynesians entered the Pacific. It is thus that we can explain how there existed in these islands at the time of their discovery by Cook, Bougainville, and other navigators of that period, a number of weeds that have their homes in America.
(5) It is not considered that the distribution of aboriginal weeds can materially aid the ethnologist in his study of the early history of man, since birds are regarded as the chief distributors of their seeds and fruits. Whilst man has prepared the conditions for the growth of weeds, the bird has usually brought the seeds.
(6) Amongst interesting plants concerned with man in the Pacific are Aleurites moluccana and Inocarpus edulis, which are regarded as in the main distributed through man’s agency. Gyrocarpus Jacquini is viewed as a tree originally widely dispersed by the currents in the Pacific, but now becoming extinct.
CHAPTER XXIX
BEACH AND RIVER DRIFT
In the south of England.—On the coast of Scandinavia.—In the Mediterranean.—Southern Chile.—Very little effective dispersal by currents in temperate latitudes.—Cakile maritima.—In tropical regions.—River drift.—River and beach drift of Fiji.—Musa Ensete.—The coco-nut.—River and beach drift of Hawaii.—Comparison of the beach drift of the Old and New Worlds.—Summary.