PAPERS ON BIOLOGY AND AGRICULTURE 115 



NOTES ox HAWAIIAN BOTANY WITH SPECIAL 

 KEFERENCE TO THE FUNGI 



F. L. Stevexs. Uxn'EESiTY OF Illinois 



Hawaiian botany as well as zoology is of especial in- 

 terest for several reasons. The extreme isolation of the 

 islands, which lie some 700 miles from any considerable 

 islands and nearly 2,000 miles from continental land, 

 renders the question of the origin of the flora an interest- 

 ing and important problem. Some botanists see in the 

 plant distribution evidence of j^revious land connection, 

 of land bridges whereby the ancestors of the present flora 

 and fauna arrived, while others explain the present con- 

 dition as due to the wind and water currents, even going 

 so far as' to distinguish separate waves of migration 

 correlated with the geologic record of America, the sub- 

 mergence of Panama, and the consequent changes in 

 ocean currents. The islands are entirely volcanic; 

 Kauai, the northernmost, is doubtless the oldest ; Hawaii, 

 the southernmost, doubtless the youngest. Only coral on 

 lava or lava itself may be trod upon. All of the islands 

 have been repeatedly subject to lava ovei*flows, Kauai 

 long ago, HaAvaii recently, perhaps today. These over- 

 flows have naturally profoundly influenced vegetation. 

 In Kauai all has been quiet for ages, and immense can- 

 yons have been cut in the once hot lava. On Hawaii many 

 lava flows during the last century and countless ones 

 earlier have solidified into stationary stone rivers, often 

 30 to 60 miles long by several miles wide. These flows of 

 all ages on Hawaii and their eroded counterparts on 

 Kauai give most fascinating fields for ecological study. 

 The character of erosion has produced wond-erful can- 

 yons, cliffs and gorges, and miles of knife-edge ridges 

 with abnipt changes in elevation and sudden transitions 

 in rainfall. The top of Mt. Waialeale, Kauai, is the wet- 

 test place in the world, having a precipitation of 549 

 inches in 1920; other sections, Uuu Kea, had only 7.9 

 inches in the same year. These conditions also afford 

 wonderful ecological opportunities. Sharp localization 

 of flora is found on the two sides of a mountain or the 



