228 RoBINSON: PTERIDOPHYTA OF THE HAWAIIAN ISLANDS 
These winds together with the ocean currents make the tempera- 
ture of the Hawaiian Islands several degrees lower than that of 
the West Indies, which are in the same latitude. At sea level it 
ranges from 16° to 30° C., while at an elevation of 365 m. it is 
about 20° C. 
There are few wild plants in the islands that seem to owe their 
origin to northwest America, though a pine log of great size, 
evidently brought by the North Pacific Drift Current, has been 
known to reach the island of Maui. A correspondence between a 
number of South American and Hawaiian forms has been traced 
among flowering plants, but the affinities of the ferns seem to be 
with those of the islands to the southwest rather than with those 
of the mainland, while a large number of species are endemic. 
The extreme lightness of the spores makes their suspension in 
currents of air for long periods possible, and also may account for 
their transfer over great distances. In prehistoric times the 
journey of two thousand miles from the Society Islands was 
probably made several times in open boats, and since ferns were 
used in the religious rites of the islanders, some species may have 
been introduced in this way. 
The material for this study consisted of the collections im the 
herbarium of the New York Botanical Garden (indicated by C); 
that of the Royal Botanical Garden at Berlin, Germany (indicated 
by B), the Bernice Pauahi Bishop Museum at Honolulu, H. I, 
(indicated by BM), the National Herbarium at the Smithsonian 
Institution, Washington, D. C. (indicated by N), and the het 
barium of Vassar College, Poughkeepsie, New York (indicated by 
V). Ina few cases comparisons have been made at Kew throu 
the kindness of Mrs. N. L. Britton of the New York Botanical 
Garden (indicated by K). The writer spent seven weeks in the 
Hawaiian Islands, in the summer of 1909, in collecting ferns and 
observing ecological factors of their habitat. 
When Captain Cook made his last South Sea voyage in 17769 
during which he discovered the Hawaiian Islands, he was accom: 
panied by David Nelson, who made collections of ferns and other 
plants, now preserved in the herbarium at Kew, th 
Linnean Society of London, and that of the British 
Landings were made upon Kauai and Nihau in January } 
