20 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
The temperature at the head of Punaruu Valley, at daybreak, was noted as 
12.7° C., truly a low figure for the tropics. 
Personal observations were made in the case of certain points along Fautaua 
Valley, from its mouth up to a point about halfway to the geometrical center of the 
island. Maximum and minimum readings at these points, as well as certain isolated 
observations, are given in table 6. The scale of a continuous-recording instrument 
placed at the highest station shows a diurnal curve that agrees with the coastal 
records as regards the times of highest and lowest points. Indeed, the comparable 
curves are almost exact counterparts in their characteristics, although the absolute 
values are about 6° or 7° C. lower for the higher station. 
TaBLe 6.—Temperature records at different levels in Fautaua Valley, Tahiti. 
July 12. July 7-12. 
j Distancehn emo 
Station. mate ar 
from sea.) |. = Minimum 
altitude. : Temper- . Temper- Maximum 
Time. Time. tempera- 
ature. ature. temperature. 
ture. 
miles. feet. h. m. NXE h. m. Xn Xe 26; 
Road at entrance........ 0.25 25 22 ep ein 28595. |steei eisvsysetcs bvsuzie aksts Jesbes 
Along footpath.......... 0.75 50 DBE) Sop 11 28.5 7 30a.m 20.5 29.4 20.0 
Dead tree, snail area..... 325) 425 33 SY joy fin 25.0 8 15 a.m. 18.3 Xf 18.3 
Near rock, uppersnailarea| 4.25 550 3 47 p.m. 25.0 8 33a.m 18.8 2 tf 18.3 
“Fort Faa-rahi”........ B78 Nie 1A Sporn || 23.0 19 Basa, || a7Q Wreorwes LO 
22.2 on ground. 4 
It is therefore evident that although the temperatures of various points along 
the shore are practically the same, the atmosphere becomes cooler at the rate of 
about 5° C. for every thousand feet of ascent towards the central peaks. The reason 
for the absence of Partule from the highest central areas of the island is found in 
the fact that lowered temperature inhibits their activity. 
It must be noted, before passing on, that the relation between increase in alti- 
tude and decrease in temperature must necessarily be modified by other circum- 
stances. When valleys trend north and south there will be in general a lower 
temperature for any given level than in a valley that runs east and west, into which 
the sun’s rays enter during a larger part of the day. And furthermore, ceteris 
paribus, a valley with high and steep sides will be cooler than a shallow depression, 
or one whose sides slope gradually upwards. 
Throughout Polynesia the rainfall is abundant, and humidity (like the tempera- 
ture) is relatively high and constant. ‘The factors are the great areas of ocean from 
which moisture is drawn, and the heavy trade-winds that carry this moisture to the 
land-masses, where, on the cooler mountain heights, clouds are formed and rain 
falls heavily. After about 9 a. m. every day, the clouds begin to mass upon the 
mountain peaks and cover a lesser or greater part of an island until late in the after- 
noon. Very rarely, and then only during the season of diminished rainfall, does the 
profile of the central mountains of Tahiti appear during the middle of the day. 
Yet even in an island like Tahiti, situated in a region of great heat and humid- 
ity, the conditions of moisture vary in different parts of the land-mass, owing to 
