398 BOTANICAL GAZETTE [NOVEMBER 
island. The Puu Waa-waa region, like some of the pit craters and 
kipukas, is a botanical oasis in the midst of a desert and harbors 
much material of unquestionable antiquity. 
VOLCANIC DusT.—In order to treat comprehensively the ecologi- 
cal aspects of the lava regions, it is necessary to include a statement 
concerning volcanic dust (fig. 13). The Hawaiian volcanoes have 
Fic. 13.—Pumice fields, Kilauea volcano; chief plants, Metrosideros polymorpha 
and various xerophytic species; white patches in foreground, lichens; in distance, to 
right, is ohia forest, Metrosideros polymorpha. 
been conspicuously quiescent in their activities during historic 
times; the outpourings of lava have been relatively gentle and 
non-explosive. There is much evidence, however, which indicates 
tremendous explosive eruptions at various periods in the history 
of the volcanoes, and at least one of these (Kilauea, 1790) has 
fallen within historic times. 
Among the most abundant of the varied products of these 
explosive eruptions, in the Hawaiian Islands as in the case of vol- 
canoes generally, is volcanic dust. Extensive deposits of dust 
