As to the wood of which the fire-sticks are made accounts differ. According to Dr. H. Schinz the holed or female stick is of a soft wood, the pointed or male stick of a hard wood, generally of the [Sidenote: The male fire-stick made of the sacred _omumborombonga_ tree.] sacred _omumborombonga_ tree (_Combretum primigenum_). According to Mr. C. G. Büttner, neither of the sticks need be of a special tree, and any wood that happens to be at hand may be employed for the purpose; only the wood of the thorny acacias, which abound in the country, appears to be unsuitable.[714] Probably the rule mentioned by Dr. Schinz is the original one, and if in some places the wood of the sacred tree has ceased to be used to light the holy fire, the reason may be simply that the tree does not grow there, and that accordingly the people are obliged to use such wood as they can find. We have seen that a branch of the sacred _omumborombonga_ tree is regularly planted beside the village hearth, but that in default of it the people have to put up with a bough of another kind of tree, the _omuwapu_ (_Grevia spec_).[715] Such substitutions were especially apt to be forced on the Herero in the southern part of the country, where the _omumborombonga_ tree is very rare and forests do not exist, the larger trees growing singly or in clumps. In the north, on the other hand, vegetation is much richer, and regular woods are to be found. Here, in particular, the _omumborombonga_ tree is one of the ornaments of the landscape. It grows only beside water-courses, and generally stands solitary, surpassing a tall oak in height, and rivalling it in girth; indeed, so thick is the trunk that were it hollowed out a family could lodge in it. Unlike most trees in the country it is thornless. Whole forests of it grow to the eastward of Hereroland, in the direction of Lake Ngami. So close is the grain and so heavy the wood that some of the early explorers gave it the name of the “iron tree.”[716] Hence it is well adapted to form the upright stick of the fire-drill, for which a hard wood is required.