AN ECONOMIC STUDY OF ACACTIAS. 3 
CHARACTERISTICS OF VARIOUS SPECIES. 
SOIL AND MOISTURE REQUIREMENTS. 
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Acacias form one of the most conspicuous associations of al! those 
which group themselves close to deserts. While they do not con- 
stitute a true desert species, they nevertheless carry tree life well 
into the desert regions, becoming shrubby and scattered. In fact, 
some species, such as Acacia greggi, one of the most valuable lac-insect 
bearing species, will thrive with only 3 inehes of rainfall; some 
grow on inland sand dunes far from ocean influences. With a few 
notable exceptions, the acacias are preeminently adapted to poor 
soil and rainless summers and to semiarid conditions, though most 
of them respond to good soil and abundant moisture. Their great 
drought-resisting qualities come from their deep, strong root systems 
and from their leaves, which are chiefly phyllodes, or flattened 
stems, with sensitive specialized powers of movement by which - 
evaporation may be greatly lessened. 
A light, warm, well-drained soil, if cultivated, will produce rapid 
growth, and the rich and heavy sole which some of the eucalypts 
demand for their best development are not necessary: for the acacias. 
The most prominent exception to this is Acacia melanoxylon, or “black 
wood,”’ which produces choice timber but has httle value for tanning 
unless the tannic acid is concentrated by the extract method. This 
is a river-bottom species, associated with Eucalyptus globulus and 
other trees of that type. 
Acacias readily adapt themselves to a heavier precipitation ond 
more tropic conditions than characterize their native soil, as proved 
by many years of growth in the Hawaiian Islands and on the Natal 
coast of Africa. Indeed, many species, as with the eucalypts, when 
introduced elsewhere, may grow even more rapidly than in their 
native region. But mainly the significant fact about the tree, so 
far as moisture conditions are concerned, is that it does not require 
a heavy annual rainfall nor any summer rain. It is this character- 
istic which renders it valuable on the southern Pacific coast and in 
the Southwest. It must be kept in mind that the trees are only 
half hardy as regards frost, and will not endure a temperature below 
16° F. or 20° where the cold is likely to be sustained. 
So far as known, no other semitropic trees of high economic value 
possess to so great an extent the ability to thrive upon and to 
improve a great variety of arid and sterile soils. Through their 
agency large areas of land unfit for ordinary cultivation, and at 
present producing only a scanty pasturage at best, may be reclaimed 
and utilized. Recent discoveries in the nitrogen-fixing qualities of 
the legumes point to the possibility of a hitherto unrecognized value 
mm acacia growing. 
