260 MacCAuGHEY: THE STRAND FLORA 
The unique position of the Hawaiian Islands, as the most 
northern group of the great Polynesian island series, and as a 
region of extreme isolation, gives particular significance to 
its strand flora. The absences from this flora are as important 
criteria as are the species actually present, *and in many ways 
contribute as effectively to our knowledge of the origin and history 
of Hawaii’s strand flora. 
The attempt is here made to present a salient account of the 
Hawaiian littoral flora, both from the standpoint of content and 
dispersal, and also from the ecological viewpoint. In the latter 
phases of the subject the author has been particularly interested. 
During a residence of nine years in the islands he has made hun- 
dreds of excursions along Hawaiian strands, including the prin- 
cipal islands of the archipelago. The present papers incorporate 
the important data of these field studies. 
A noteworthy feature of the littoral floras of the tropical 
Pacific islands is their remarkable similarity. As Hedley (’15) 
expresses it: ‘The same species are repeated from atoll to 
atoll over enormous distances across the Pacific Ocean. The 
identity of the vegetation possessed by tiny islets separated by 
thousands of miles of deepest ocean is very striking, since para- 
doxically they present a greater continuity of life range than any 
continent can show.’’ Many of the more common Hawaiian lit- 
toral plants occur on practically all the islands of the archipelago, 
along an axis of nearly two thousand miles, whereas the montane 
species are highly localized. 
Just as the interior mountainous districts of a high Pacific 
island contain the majority of the endemic species, so the strand 
regions are characterized by a majority of the cosmopolitan or 
wide-ranging species. Tansley and Fritsch (’05) find two main 
causes for ‘‘the striking uniformity of strand plants through the 
tropics—first, the great similarity of life conditions prevailing on 
tropical coasts, and secondly, tropical strand plants are mostly 
adapted for distribution by ocean currents.’’ These factors will 
be considered in detail in later sections of this paper. 
As will be shown later, the Hawaiian littoral flora comprises 
many species that occur in other parts of the Pacific, and in many 
other parts of the world. The mountain flora, on the contrary, 
