Of Oahu, has an irregularly circular form with a maximum diameter of about 25 m.
Towards the close of the 19th century William Hillebrand found 365 genera and 999 species, and of this number of species 653 were peculiar to this part of the Pacific. The number of species is greatest on the older islands, particularly Kauai and Oahu, and the total number for the group has been constantly increasing, some being introduced, others possibly being produced by the varying climatic conditions from those already existing.
In the older valleys on the islands of Kauai, Oahu and Maui, as well as on the lowland plain of Molokai, the soil is deeper and usually, too, the moisture is retained by a heavy clay.
The sugar farms are mostly on the islands of Hawaii, Oahu, Maui and Kauai, at the bases of mountains; those on the leeward side have the better soil, but require much more irrigating.
A few bananas and (especially from Oahu) pineapples of fine quality are exported; since 1901 the canning of 3 The entomological department of the Hawaii Experiment Station undertakes " mosquito control," and in 1905-1906 imported top-minnows (Poeciliidae) to destroy mosquito larvae.