FLORA OF THE GROUP. 195 



Hillebrand and others have found it convenient to group the flora of the 

 islands into different zones based mostly on the elevation they occupy. There 

 are six of these arbitrary zones that with a little experience can easily be recog- 

 nized since their floras are more or less well defined though, of course, intergrad- 

 ing from one zone to another to some extent. 



Flor.vl Zones: The Lowland Zone. 



For the purpose of this sketch of the flora of the Hawaiian Islands it will 

 suffice to speali of a few of the more important plants in each zone, beginning 

 at the sea-coast, where there is a peculiar strand vegetation, and from there make 

 an ideal ascent of the mountains, taking one zone after another until the summit 

 of the highest mountains have been explored. 



Starting with the plants of the lower zone we have species tliat thrive at 

 the sea-shore, often at the very water's edge. This is known as the littoral flora 

 and always grows along the sea-shore or the margin of brackish water, usually 

 within sound of the sea. It seems to be indifferent to the salt in the soil. 

 Almost all of the plants of this zone are ocean-borne and widely distributed 

 species. As a rule they have fleshy stems and leaves and possess great vitality. 

 They may be uprooted by the waves, borne out to sea by the tides, and carried 

 away for long distances by the currents, to be set out again by the action of 

 the waves on some foreign shore. The plants found growing on Midway, Laysan 

 and Lisiansky, and in fact all the low Pacific islands and shores, are of this 

 littoral type. On Laysan the writer collected twenty-six species that must all 

 owe their origin to the method of transplanting just described. 



Common Littoral Species. 



There is veiy little variation in temperature and conditions at the sea-shore 

 throughout the group, and as a result we generally find the condition of plant 

 life fixed and uniform on all of the islands. The same littoral species may occur 

 wide-spread about the shore of the different tropical islands, \vhile the genus 

 to which the species belongs may be represented inland where conditions are 

 more variable by several species, often one or more such species being peculiar 

 to each island where the genus occurs. An interesting example of this is found 

 in the case of the genus Scavola — the naupaka of the natives with a wide 

 spread shore species.^ The .species of the genus are all small shrubs bearing 

 white or pale blue and occasionally yellow flowers that are peculiar in that the 

 corolla is split along the upper side to its base. Owing to this peculiarity the 



^ Scwvola Lobelia. 



Description of Plate. 



1. Hawaiian Mahogany [Koa] (Acacia koa) from the koa forest near the volcano 

 Kilauea. 2. Tree Ferns (Cibotium sp.) in the fern jnngle near the Volcano House. 3. 

 Lichens on trees; a chareteristic of the forests aboTe 2000 feet. 4. Lauhala {Fandanus odor- 

 atissimus) by the sea-shore on Hawaii. .5. Staghorn Fern [Uluhe] (Glelchenia linearis). 

 6. A Staghorn Fern tangle near the volcano Kilauea. 7. Wilivvili (Erythrina monosperma) . 

 8. Apeape (Gunncra pctaloides), showing the comparative size of its sijlendid leaves. 



