480 
PACIFIC SCIENCE, Vol. XX, October 1966 
TRANSECT 1 
• 0 0 00000 COO 05 comcoi 00 10010 
,,,,,, 11,111111 ;V V \' V . V \\ . ' \\K \a A\ V \v Av .V \\ / / / / 
.nO.V 
0 fM0 
0 
0 
Eucalyptus 
Ground cover 
Soil type 
I. alba 
I J /■//... 
. . .Themeda^Hekropogon 
group 
m 
38b 
....Black clay soil 
.£ papuana 
\\\ \\\ \\\ . . . 
. . Ihemeda-Capillipedium 
group 
...Texture-contrast soil 
A conferti/ loro 
\l/ T \l/. . . 
. . Jhemeda~Sehima 
group 
. . .Sehima ^ Heteropogon 
series 
....Red regosol 
Fig. 2. Diagram of the transects, showing the distribution and mutual proportions of the Eucalyptus 
species, and the distribution of the ground cover groups and of the soil types. 
trunk. The horizontal roots of E. papuana are 
often oval in section with the long axis vertical, 
and divide at or near the base in several hori- 
zontal roots above each other (Fig. 4). 
Horizontal roots run for distances up to 
about 25 m more or less parallel with the 
surface, often not deeper than 0.2 m, only 
very gradually tapering. Near the base vertical 
roots branch off from horizontal roots, and are 
particularly common in some specimens of E. 
alba. In some cases these roots run down verti- 
cally more than 1.5 m, but more often they 
gradually bend away obliquely, and may even 
bend up and penetrate the topsoil again, where 
they continue horizontally. 
The way in which the main roots of E. alba 
branch off from the base of the trunk is dif- 
ferent from that of E. papuana and E. conferti - 
flora, where they gradually emerge from the 
base. In the case of E. alba the trunk is usually 
a little swollen, but sometimes is considerably 
so. With a trunk diameter of 24 cm, the diam- 
eter of the base may vary between 30 and 45 
cm. Just below the surface the base is con- 
stricted, under which constriction the main 
roots branch off. 
The taproot, if present, may reach a depth 
of 1.3 m but is usually shorter. It branches off 
under acute-angle, thick roots, which show the 
same features as described above for the ver- 
tical roots. One specimen of E. alba was found 
which lacked the cluster of horizontal roots 
but which had a very stout taproot. 
Tree roots with diameters of 1 cm or less, 
whose origin could not be traced, were found 
scattered at depths of 1.3 m, and rootlets with 
