In great contrast stands the vegetation both of Kauai and of the Kaala range of Oahu. Most of Mann's and Wawra's new species come from Kauai, and Mr. Knudsen's collections have added still more to them. Even the species which that island has in common with others generally vary from them in one or more particulars. The Kauai species of the leading Hawaiian genera are in all instances the most specialized, to be distinguished by more striking characters than the others. Examples are : Schiedea, Raillardia, Dabantia, Campylotheca, Lipochaeta, Pittosporuni, Pclea. The proportion of species peculiar to Kauai with species peculiar to all the other islands is about 67 :382, or 17.5 :100." Much may be learned from a study of the origin of the plants of the archipelago. Out of a thousand species, as described by Hillebrand, there are five hundred and forty-seven exogens, thirty five endogens and eighty-four vascular cryptogams„ chiefly ferns ; of an exclusively Hawaiian origin, sixty-six per cent. Of the re mainder there are first, many tropical species widely distributed throughout Polynesia ; second, many that are allied to North American forms ; third, a smaller number resembling plants in Asia and Polynesia ; fourth and fifth, the smallest numbers, from Australia and Africa. The plants useful for food or fabrics have probably been introduced by the natives. They are such as the plantain, banana, coconut, breadfruit, pineapple, yam, taro, cotton, peach, fig, sugar cane, orange and alligator pear. Various weeds, mostly undesirable or noxious, particularly the lantana, have come with American immigrants. A few characteristic indigenous Hawaiian plants are the koa wood, lately called Ha waiian mahogany, the hau and milo, malvaceous species, silver sword and the ohelo, a huckleberry of the size and often color of the cranberry. Some plants become shrubs or trees, as the lobelia, violet and many Compositae. All the plants are either exotic or else have been derived from species brought by the waves, by animals or by man.
A good illustration of the origin of the vegetation is the screw pine, pandanus or lauhala. This is a small tree growing at the sea shore. The seeds are edible and are gathered together in bunches somewhat like a small pineapple, each one being a wedge with the small part inside. These seeds will stand satura tion in water for months without losing their vitality. Hence they may be carried hundreds or thousands of miles from the place of their nativity, and when washed inland by unusually high waves will be placed where they will sprout and grow up. I once saw a place in Kauai where hundreds of young lauhalas had started to grow near the sea shore just like the multitude of young maples in New England. In both cases the majority die, but some
will live, and upon the islands the lauhala will be the means of the increase of dry land.
There is no tree with a wider range in the Pacific than the pan danus. And it was in existence in the Triassic period in Europe. It is therefore one of the oldest and most persistent of plants, and the one best fitted to start plant life upon the isolated volcanic islands for the first time peering above the waters.
The accepted doctrine for the covering of the islands of the Pacific with vegetation is not that they were specially created where now found, nor that they are tips of a submerged conti nent, but that the barren rocks attracted the seeds brought by ocean currents from all sides, and that when the plants in the new region found the conditions favorable for a luxuriant growth they flourished exuberantly and developed into the new species said to be indigenous. And the various examples just cited prove that there is a constant development both of vegetable and ani mal life in the new habitats.
Oahu has been celebrated for the abundance of the peculiar land shells known as Achatinellidac or agate shells living natur ally upon it. There are over two hundred species of them, rep resented by Boo or i,000 varieties, and each of these forms is confined to a small section of territory in the forests of the two ranges of mountains. Each valley has its own peculiar varieties. The most widely divergent forms of one group will be found in the valleys that are most distant from each other, while intermedi ate varieties will be found in the intermediate valleys. The species living far apart cannot be connected by minute gradations without bringing in some of the forms found in the intermediate territory.
Granting that these organisms are all descended from one ori ginal stock, the diversity at present existing has been supposed to be produced by exposure to different environments, cooperating with a series of isolations ; and if the diversities have been sys tematically developed it must be possible to locate the home of the original species and the routes of their migrations. It will be interesting also to discover whether some one of the islands car ried the original animal, whose descendants migrated to other parts of the archipelago, and whether the developments have corresponded to the geological ages of the different areas. While no one has yet succeeded in discovering the order of develop ment, there is a suggestion that the ancestor of the Oahu forms came from Kauai—and it is a fact that these creatures are very scarce upon Hawaii. This order would correspond to that al ready mentioned about the plants, and so far forth both are in agreement with the geological conclusions.