THE COLLECTIONS FROM TAHITI AND THEIR INVESTIGATION. 33 
feet), eastward and northward to Aramaoro (4,848 feet), and thence to the coast 
along the ridge bordering Faarumai Valley on the west. Papara is bounded on 
the west by the ridge beginning at the southwestern corner of Vahiti nui that rises 
to Mount Ivirairai (5,556 feet), and to Mount Mahutaa (4,943 feet), and continues 
on to join the southern border of the great Papenoo basin; the eastern boundary 
runs coastwards from Mount Tetufera along a prominent ridge. In general, each 
political district includes at least one large valley as a salient topographical feature, 
and consequently each administrative section is also an ecological region centering 
about the deep valley area or areas. 
In another way, the island is divisible into sectors of high land that lie between 
the major valley clefts. To the west of Papenoo Valley, one such sector rises to” 
the highest peaks, Mount Orohena and Mount Aorai, and ends beyond at Fautaua 
Valley; in this there are many valleys of lesser extent and depth which fail, however, 
to reach the center so as to articulate with either Papenoo or Fautaua. Between 
the latter and Punaruu Valley is another sector in which are located Tipaerui 
(plate 15a) and Taapuna, as well as lesser elements. From Punaruu to Temarua the 
land-mass is extremely regular and is somewhat distinctly divided by Orofere Valley 
into northern and southern components. ‘The next sector extends to Vairaharaha 
and Vaihiria, and contains many long, narrow valleys. So the rest of the whole 
island is organized into land-masses and lesser valley systems, in ways that are 
sufficiently indicated by the illustrations, or that may be described in further detail 
in the discussion of a given species or variety and its distribution. 
Taking a more general view of the whole of Tahiti nui, it is convenient to 
divide this land-mass into four major quadrants that form as many well-defined 
ecological sections, so far as their general climatic conditions are concerned. The 
line running from the Isthmus of Taravao at the extreme southeast to Motu Tahiri 
at the northwest coincides with the direction of the prevailing winds laden with 
moisture. A line at right angles to this, viz, from Maraa at the southeast to the 
district of Tiarei at the northeast, completes the partition of Tahiti nui into quad- 
rants and defines the boundaries between the wet southern and eastern sectors on 
the one hand and the drier western and the driest northern regions on the other. 
For purposes of convenience in the detailed description, however, the point of 
contact between the eastern and northern quadrants is shifted to the west, so as to 
lie between Farapa and Papenoo Valleys. 
It has been stated that lesser ancient vents lie outside of the main central 
region, from which run deep valleys of a secondary order, such as Tipaerui (plate 15a). 
Naturally the valleys of this grade are more isolated from one another and from 
the primary elements as well. Many of them do indeed reach inland for a con- 
siderable distance, but their side ridges are much higher and steeper than in the case 
of primary valleys. Between the valleys of the second order are still others of 
lesser radial extent (¢. g., Papehue Valley, plate 15), but still large enough to collect 
streams of some size. Like the larger ones, these tertiary elements also differ much 
in radial extent and in the heights of their sides, in which they are cut. It is 
possible to recognize also elements of a fourth order (plate 162), while finally there are 
