1917] MACCAUGHEY—HAWAIIAN FLORA 401 
of Kea, at an elevation of 14,000 ft., is a small perennial pond, 
Wai-a’u, about 125 ft. in diameter. This pond is situated in an 
ancient crater basin and is fed by the melting snow. It is frozen 
during a major part of the year, even in midsummer. Ice occurs 
in the deep fissures and caverns in the neighborhood of the sum- 
mits of Kea and Loa throughout the entire year, and during late 
winter it is relatively abundant. 
SUMMIT REGIONS.—The treeless character of the summits has 
already been mentioned. The timber line is very low, indeed 
, unusually low as compared with that of mountains in other parts 
of the world. Hatt’s’ explanation so accurately summarizes the 
local conditions that it is reproduced herewith: 
Elevation has put a sharp limit to the forests on the islands of Hawaii 
and Maui at from 6000 to 8000 ft. This leaves very large areas of Mauna Loa, 
Mauna Kea, Hualalai, and Haleakala devoid of forest, and they have always 
been so. The mountains of the other islands, being under 6000 ft., are forested 
to their summits. Six to 8000 ft. is a surprisingly low timber line, considering 
the favorable conditions of soil, moisture, and temperature which prevail at 
that altitude in Hawaii. The sufficient reason seems to be that the species 
composing the native forests are all representatives of the torrid zone, and in 
these islands, which lie right at the edge of the Tropics, find their limit at the 
low altitude named. 
SEEPAGE.—The physical structure of the lava flow is such that 
Seepage takes place with extreme rapidity, and in the typical 
flow country there is absolutely no surface water. This abnormally 
high percolation greatly heightens the physiological aridity of the 
lava as a substratum for plant life. Both the a-a and the pa-hoe-hoe 
types of lava are highly ramified with crevices, caverns of all sizes, 
and long tunnels or lava “‘tubes.’’ Thus a vertical section of the 
mountain would reveal a copiously spongy texture, with large 
caverns sloping toward the sea. Dawna’s® account may be appro- 
priately quoted in this connection: 
Over the leeward sides . . . . where rains are infrequent, a black desert 
everywhere prevails, and there is, with rare exceptions, only an alternation 
between the smoother fields of cooled lava and the rougher districts of scoria. 
Yet over the barest fields there is always a sprinkling of verdure, growing 
5 Hatt, W- L., Forests of the Hawaiian Islands. 1904 (p. 16). 
6 Dana, J. D., Geol. U.S. Explor. Exped. 10:1849 (pp. 159-160). 
