400 BOTANICAL GAZETTE [NOVEMBER 
about 50 observers, scattered at various points on the islands. 
As these observers are stationed in or near human settlements, 
and as these settlements are situated in regions of at least moderate 
rainfall, it happens that there are no records covering the areas 
which form the central theme of this paper. The great upper 
slopes of Loa, Kea, Hualalai, and Haleakala, having a total area 
much greater than that of the peripheral lowlands, are uninhabited 
waste lands and without meteorological data comparable to that 
of the agricultural. lowlands. 
The Hydrographic Survey, interested primarily in the rain 
sections and the streams, has naturally avoided the great arid and 
streamless areas which are considered in this paper. Hence it is 
not possible to present extensive tables showing accurately the 
precipitations on these arid districts. 
It is necessary to emphasize the importance of the trade winds 
as the rain-bearing winds of the islands. These winds blow from 
the northeast almost continuously through a large portion of the 
year. The main axis of the archipelago lies from northwest to 
southeast, so that the islands lie across the path of the trades, and 
hence develop strongly differentiated windward and leeward 
climates. The warm trades sweep across vast stretches of ocean 
before reaching the islands, and are consequently saturated with 
moisture. Upon striking the cool mountain slopes very heavy 
precipitation ensues, often totaling several hundred inches.* In 
this zone the luxuriant rain forest reaches its finest development. 
The leeward slopes, however, are robbed of this torrential rain; 
the winds that reach them are usually dry and parched, and the 
climate is arid or semiarid. 
SNoW AND IcE.—The high mountains of Maui and Hawaii are 
often snow-capped. This is particularly true of Kea, literally the 
“white mountain,” which is prevailingly snow-crowned from 
November to March and intermittently at other seasons. At 
the season of greatest snowfall the snow line often reaches down 
as low as gooo ft.; at other seasons there are frequently extensive 
patches of snow at the higher levels. Near the extreme summit 
+The greatest annual precipitation officially recorded in the Hawaiian Islands is 
561 inches, in 1916, on Waialeale, Kauai, by the Hydrographic Survey. 
