30 



Whether they arrived buoyed up and floated by ocean cur- 

 rents, wafted by the wind, or came as passengers on floating 

 logs or clinging to the feathers or feet of migratory birds, the 

 great distances necessarily traversed make it appear improba- 

 ble that plants or their reproductive structures reached the 

 islands frequently or in abundance. 



Hillebrand in 1880 in his "Flora of the Hawaiian Islands" in- 

 cluded approximately 1000 species of ferns and flowering plants. 

 More extensive and intensive explorations of the islands to- 

 gether with several critical monographic treatments of some of 

 the higher groups have been made since that time. While the 

 mosses and fungi have been studied, the other groups of lower 

 plants are not so well known. A careful taxonomic study of the 

 algae or lichens, for example, would undoubtedly reveal many 

 species now unknown to science. The total number of species 

 in the Hawaiian flora, exclusive of the large number of intro- 

 duced forms, while not definitely known, must certainly now 

 greatly exceed the number included in Hillebrand's "Flora." 



A great diversity of ecological conditions is found on the 

 islands, ranging from the tropical climate of the coast and low- 

 lands to the occasionally snow-clad tops of Mauna Loa and 

 Mauna Kea, and from moist, rain- and fog-swept fertile valleys 

 and windward mountain slopes to arid and semiarid ridges and 

 sand dunes on the leeward sides of the islands. This great diver- 

 sity of ecological conditions affording maximum opportunity for 

 growth and development, together with the isolation and conse- 

 quent freedom from the influence of a surrounding flora, proba- 

 bly is largely responsible for the remarkably high degree of en- 

 demism which amounts to between 80 and 90 percent. 



For purposes of a brief discussion, the flora may be consid- 

 ered under the following four categories: 



a — Native plants. 



b — Economically useful plants of early Hawaiian introduc- 

 tion and now mostly well established. 



c — Weeds, chiefly of the wayside and fields. 



d — Recently introduced plants of economic importance. 



Several unfavorable influences have had a marked effect on 

 the extent and distribution of the native flora. Hogs were in- 

 troduced in prehistoric times, and goats, cattle and horses were 

 early introduced by the whites into the islands. Many of these 



