6 DERIVATION OF THE FLORA OF HAWAII 



shallow water with the main group. There are also to the west and south- 

 west somewhat shallower areas connecting with the Polynesian region 

 to the southwest. 



As might be expected from their extreme isolation, both the fauna 

 and flora of the islands are very much specialized, and the question of the 

 origin of the organisms now inhabiting the islands is one of the greatest 

 interest. 



If the islands have been thrown up as isolated volcanic masses from 

 the ocean depths, it necessarily follows that, except for the comparatively 

 small number of plants and animals introduced through human agency, 

 all the organisms must have reached the islands from very remote re- 

 gions by such accidental means as air currents, ocean drift, or migratory 

 birds. The present indigenous plants and animals must be, according to 

 this theory, the descendants of such chance immigrants. 



On the other hand, if an ancient connection with some former large 

 land area is admitted, we may assume that the majority of the organisms 

 are the descendants of species which existed at the time when this land 

 connection was severed. 



The Hawaiian Islands lie between 1855' and 2215' north latitude 

 and 15450' and 16030' west longitude; and there is also a chain of 

 small low islands and reefs extending for about 18 in a northwesterly 

 direction. The whole chain of islands comprises in reality the summits 

 of a great submerged range of mountains apparently formed as the result 

 of enormous volcanic activity along a fissure in the earth's crust, which 

 began at the northwest and has proceeded in a southeasterly direction, 

 the last manifestations of activity being now found only in the active 

 craters of Kilauea and Mauna Loa, in the Island of Hawaii, the largest 

 and most southerly member of the archipelago. 



Except for certain coral formations, the islands are of exclusively 

 volcanic composition, and the soils everywhere composed of disintegrated 

 lava or volcanic ash. 



In marked contrast to this uniformity of soil constitution are the 

 conditions of temperature and moisture, due to the mountainous charac- 

 ter of the islands and the prevailing northeast trade wind. On the wind- 

 ward side there is a very heavy precipitation, and the erosion results in 

 deep, narrow valleys, with precipitous walls, the vertical cliffs, or "palis," 

 being a marked feature of those valleys, which usually end abruptly 

 against a high cliff over which descends a waterfall. On the leeward 

 side, especially in the loftier islands, the precipitation is very light, and 

 the ancient lava flows sometimes have remained scarcely changed for cen- 

 turies. A very remarkable instance of this is seen in the huge extinct 

 crater of Haleakala, on the Island of Maui. There is no record or tradi- 



