14 BULLETIN 5 9, HAWAII EXPERIMENT STATION 
the soil is unsuited for orchard work and should not be planted with 
crop-producing trees. The volcanic soils of Hawaii vary greatly in 
their mechanical nature. Some of these are sufficiently loose "and 
underdrained to permit of their use for orchard planting without 
plowing. The black sand and a-a soils are excellent examples of 
these. The black sand or cinderlike deposits are sometimes of con- 
siderable depth and have a thoroughly decomposed surface varying 
according to the amount of moisture received and the humus de- 
veloped. The a-a soils are very similar, but may be said to differ in 
early formation, as they originally consisted of very rough lava 
flows, the surface of which has been decomposed by the natural 
elements. The rather open structure below the surface of these soils 
affords an unusually favorable underdrainage. Most trees thrive in 
such soils provided they are given an abundance of moisture. The 
excess water in sinking away draws in the air, thus aerating the soil 
and carrying an optimum supply of oxygen to the roots. 
The Macadamia in its native condition usually is found growing 
in the rich alluvial soils bordering rivers and creeks in the coastal 
districts of the southern part of Queensland and in the northeastern 
part of New South Wales, Australia. 
THE ORCHARD 
WINDBREAKS 
In the Hawaiian Islands the Macadamia orchard should be shel- 
tered from the prevailing winds. Gentle trade winds are desirable, 
but at times they may prove to be too severe for the young trees. 
Temporary protection from wind should always be given to the 
young trees regardless of whether permanent protection is necessary. 
Temporary protection may be supplied in the form of burlap tacked 
to three stakes on the windward side of the trees. On several occa- 
sions in the Hawaiian Islands young Macadamia trees varying from 
2 to 5 years in age have blown over, not as the result of their being 
uprooted, but as the result of their breaking off in the ground im- 
mediately above the spread of the root system. The outer or sap- 
wood and bark break under the hard, twisting pressure of the tree 
continued for several hours in a strong wind ; and although the tough 
heartwood may still remain unbroken, the tree eventually bends over 
and dies. Death is certain to occur when the tree is thus injured, 
even when it is propped in place immediately after being injured, 
because the growing tissue surrounding the base of the trunk has 
been ruptured beyond recovery. 
Large, permanent windbreaks when necessary should be grown 
on the windward side of the orchard. Such rapidly growing trees 
as Eucalyptus (E. robusta), mangoes (Mangifera indica), and iron- 
wood {Casuarina equisetifolia) might be used for the purpose. 
These may be set alternately in three rows 10 feet apart and the 
same distance apart in the row. The row nearest to the prevailing 
wind should consist of Eucalyptus trees which make tall, strong 
growth; the central row should be made up of two kinds of trees, 
Eucalyptus and grafted mango trees arranged alternately in the 
row. The mango has a dense and resistant top and if grafted of 
good variety has the additional value of producing good fruit in 
