The leaves of the _Augea capensis_ are very strong in sap, but the plant is so salty that even the camels will turn away from it. This plant is found in many parts of the Karroo. An untidy-looking shrublet, the _Sarcocaulon rigidum_, is fairly abundant. A peculiarity of its structure is the sharp-pointed spines, which are specially modified stalks of former leaves. Leaves of vivid green cover these plants in the spring, and at times they are numerous enough to influence the colour of the landscape. Pink flowers appear on them in October. _The gravel plains._--The rising plains of the inner Namib, which have an altitude of 1,800 feet, some fifty miles from the coast, are swept by furious sand-laden winds for the greater part of the year. The sea-fogs rarely reach these areas, and, as the rainfall is a negligible quantity, no sign of life may be encountered for many miles, only a vast, monotonous waste of gravel and sand meets the eye. Occasionally one lights upon the typical _Sarcocaulon rigidum_, the Candle-bush or Bushman’s candle. This plant has been specially adapted to meet the conditions of the desert, and it is able to defy the hottest sun and the fiercest sandstorms. Layers of corky tissue, impregnated with a mixture of fat, wax, and resin, form the bark. This horny casing is the plant’s armour against the attacks of its enemies. It burns steadily like a wax candle with a yellow, smoky flame, even when cut fresh from the ground. THE CENTRAL PLATEAU Beginning with Ovamboland, we find considerable forest tracts of acacia, with giant baobabs, and palms and fig-trees in the more open park-like spaces. The palm zone is found some distance south of the Kunene. Grasses cover the extensive plains after rains. On the uplands of Damaraland the genus Acacia plays an important part in the composition of the flora; in many places it predominates among the bushes and also among the trees.[10] With the acacias are found other notable species, including _Combretum primigenium_, and the large _Ficus dammarensis_. The handsome Ana tree, _Acacia albida_, is frequently met with. The mountain valleys have a much more luxurious vegetation than the hills, since they are watered by the many rivulets that abound after rain.