Heller : plants of the Hawaiian islands. 767 



To the 139 introduced species enumerated by Hillebrand, 

 some 20 more have been added by the writer. The bulk of 

 them were collected in the vicinity of Honolulu. 



Of the few native trees mentioned as growing in the lowland 

 zone, Erythrina monosperma and Beynoldsia Sandwichensis appear 

 to have become extinct, at least on the eastern side of the 

 island. On this island, the five zones into which Hillebrand 

 divides the flora of the Islands, are not very applicable. The 

 lowland and lower forest zones are distinct enough. The lat- 

 ter, characterized by the Kukui tree, ascends to between 1, 500 

 to 2,000 feet. Polypodium pellucidum, which Hillebrand records 

 as occurring in the fourth, or upper forest zone, I have found 

 only in the lower zone. The other forms of higher elevations, 

 are all referable to new species, described in this paper. 



The third, or middle forest zone, extends to the summits of 

 the mountains. In this zone it is said that "the prevailing 

 trees are indeed Metrosideros polymorpha and Acacia Koa, but. 

 although they reach here their greatest development in size 

 and number, they are not confined to this zone, but extend 

 above, and descend below it." On the contrary Acacia Koa is 

 here more fully developed within the lower forest, and extends 

 very little above it. Metrosideros is found sparingly in the lower 

 forest, but is nowhere of any size, and higher is inclined to be 

 shrubby. As the summits are approached, it disappears alto- 

 gether. 



The upper forest zone, as limited by Hillebrand, and the bog 

 flora seem to be altogether wanting. 



The flora of Oahu may be divided primarily into two divis- 

 ions, that of the lowland, and that of the mountains. It is pos- 

 sible that the former may again be divided into windward low- 

 land flora and lee side lowland flora, but as I did not collect on 

 the windward side, this is a mere matter of conjecture. The 

 mountain flora falls into three divisions. Two of these are 

 found on the main range, and the third is on the Waianae 

 range. The broad, low valley of Nuuanu, with the deep gap 

 at the Pali, prevents the spread of species along the entire 

 length of the main range, thus forming the boundary line of 

 two floral areas. Many species grow on the east side of Nu- 

 uanu, which do not occur on the mountains on the west side, 

 and vice versa. 



Another peculiarity about the distribution of species, is that 

 a species may occur in any given valley, but is not found in the 

 valleys adjacent. One explanation of this fact may be that 



