412 BOTANICAL GAZETTE [NOVEMBER 
In 1912 ForsBeEs™ published some preliminary observations of 
plant invasion on lava flows. His principal findings, which coincide 
- with the observations of the writer, may be summarized as follows: 
1. Lichen flora is much more abundant on the a-a than on the 
pa-hoe-hoe and develops on the former at a much earlier date than 
the latter, other conditions being the same. 
2. Ferns (such as Polypodium and Sadleria) and phanerogams 
(such as Metrosideros and Sophora) do not establish themselves 
upon the a-a until long after they have established themselves upon 
the pa-hoe-hoe, other conditions being the same. 
3. The species occupying a recent flow are the same as those 
occupying older flows in the immediate vicinity. 
4. Soil is formed on the pa-hoe-hoe at a much earlier date than 
on the a-a. 
5. Acacia koa, a phyllodious species adapted to semi-xerophytic 
conditions, is the prevailing tree in the leeward upper forests of the 
middle zone, finally establishing itself upon the ancient flows as the 
dominant and final type. 
Altitudinal ranges of lava flow species 
Horizontal zonation with reference to altitude is strongly 
developed on the slopes of the Hawaiian mountains. As one 
ascends a great volcano like Loa or Kea, one finds pronounced 
changes in the vegetation with every thousand feet increase in 
elevation. From the standpoint of this paper the following large 
zones or belts may be recognized: lowland (littoral to 1500 ft.), 
lower forest (1000-2000 ft.), middle forest (1800-6000 ft.), upper 
forest (6000-g000 ft.), summit (gooo-nearly 14,000 ft.). The 
summits of Kauai, Oahu, Molokai, West Maui, and Kohala rise 
to 4000-6000 ft. only and are very boggy. They are considered 
in another paper.“ The point must be emphasized that there is a 
very considerable variation in the altitudinal limitations of these 
zones on the mountains of the different islands and on different 
slopes of the same mountain. In some regions the upper forest 
3 ForBEs, C. N., Plant invasion on lava flows. Occ. Pap. Bishop Mus. 19f2.- 
™ MacCavuGHey, VAUGHAN, Vegetation of the Hawaiian summit bogs. Amer. 
Bot. 22: 45-52. 1916. 
