SRE INTRODUCTION. 
The preceding digression establishes one indisputable fact, viz., 
that volcanic action in the fissure of the earth’s crust over which 
the Hawaiian group has been built up proceeded gradually, some 
irregularities excepted, from west to east. Geologists might hes- 
itate to infer from this the absolutely greater age of the western 
islands, for geological evidence alone would not exclude the 
supposition that all the islands of the chain were elevated at 
the same time and that the volcanic activity only died out sooner 
in the western than in the eastern islands. But here botanical 
evidence steps in to furnish the proof that in reality the age of 
the different islands rises in progression from east to west. It 
may be stated simply in these few words, that the flora of 
Mauna Loa is the poorest and most uniform, and that of Kauai 
the richest and most individualized in species, and that on the 
whole the intervening islands follow the same ratio when 
allowance is made for difference in heights; for high mountains 
offer a greater diversity of climate, and, therefore, suitable con- 
ditions for many plants which cannot live in lower zones. 
The monotony of the forests of Puna, Kau, and South Kona, 
on Hawaii, will strike every attentive visitor and disappoint the 
botanical collector by the scarcity of the harvest. This can hardly 
be ascribed to the periodical destruction of forests by lava streams, 
for these follow with long intermissions, affect only limited areas 
at a time, descend mostly down the northeast slope, and it is 
surprising to see how quickly the ruin is repaired, how speedily 
decomposition takes place in the lava when exposed to the in- 
fluence of copious rains and the trade-winds. In 1862 I visited 
the lower end of the lava stream which in 1856 had cut its 
way through the forests toward Hilo. A belt of thirty feet in 
width on each side of it was covered with a shrubby vegetation 
which had already attained a height of three to five feet. In 
the break of the pali of Oahu at the head of Nuuanu valley, 
through which the trade-winds sweep with intense force nearly 
the entire year, one could observe hard, compact basalt gradually 
softening until it could be cut with a pocket knife. And with 
how little soil plants are content when favored by copious rains 
is exemplified by the fact that the natives of Puna, Hawaii, 
se good crops of sweet-potatoes in the hollows and cracks of 
bare lava by simply covering the budding sprigs with decayed 
leaves and herbs. In the same region I once saw a cocoanut 
lying on smooth pahoehoe lava which had germinated there and 
sent off a root for a distance of eight inches until it met a 
