Deserts 
from the injured surface, at once covers over and gums 
up the scar, so that but little water can be lost through 
a wound, 
Against the browsing animals, which swarm in such 
country, they are especially well protected by thorns of 
a formidable character, or in some Australian cases by 
their bark, which contains some 26 to 48 per cent. of 
astringent tannin. 
When one visits the acacia scrub in those rare places 
where it is still in its natural condition, scarcely traversed 
except by some wandering slave-raider or roving Bedouin, 
it is the abundance of game that impresses every traveller. 
Herds of zebra, ostriches, the gaunt and indescribable 
babiroussa, large-eared and long-necked gazelles, and 
other antelopes may or used to be seen continually. This 
was the case, ¢.g., in the Taru desert of East Africa. 
Hunting is difficult, for the long necks of many of the 
animals are quite invisible against the dull yellowish- 
brown background, so that they can see long before they 
can be seen by the sportsman. In such places it is more 
than probable that in the struggle between plant and 
grazing beast it is the first that is gaining. 
Those animals, not improbably, assist rather than in- 
jure the vegetation. Their manure is scattered over 
the dry soil, which is for the most part entirely of 
mineral origin, and makes it a better and richer loam 
(see p. 198). 
Such acacia scrub is extraordinarily variable. In 
some places it is almost a forest with closely set trees ; 
elsewhere the trees are scattered, and the ground be- 
tween them is dotted with scanty tufts of wiry grass 
or sedges. Especially near the desert proper one may 
find an “orchard steppe,” so called from the scattered 
little trees, about 20 to 30 feet high, which are not 
unlike apple or pear trees. 
178 
