_The sandy plains and dunes._--Further inland _Salsola Zeyheri_ is common. This low, tight-looking shrub, grey in colour, about 2 to 3 feet in height, has considerable value, since it forms good food for the camels used for transport purposes. Coarse dune-grasses are found in sheltered patches. The _Mesembrianthemum_ is a characteristic Namib plant; it grows on rocks as well as sand. _The rocky hills._--Here we find a more varied vegetation. The well-known Kokerboom (_Aloe dichotoma_) is a conspicuous feature. It is interesting to notice that the name Koker or Quiver (D. _koker_, a case sheath; G. _Kocher_, a quiver) was given to this tree because the Bushmen and Hottentots used the pithy branches to make quivers for their poisoned arrows. Even more numerous than the _Aloe dichotoma_ are several species of _Euphorbia_. Schinz, it may be noted, has described the eastern edge of the desert as a Euphorbia-steppe.[8] The _E. gummifera_ is, perhaps, the most noticeable plant, and in the Garub region this species abounds. It forms compact bushes, 3 to 6 feet in height, and its grey twigs have rather an unpleasant scent, while they contain an unusually rich supply of milk juice. The _E. cervicornis_, the olifant melkbosch of Little Namaqualand, is found occasionally. A little plant that crouches behind rocks or isolated stones is the dwarf shrublet _Pteronia succulenta_, whose main stem is often bent over at a right angle by the fierce winds as soon as it pushes its head above the shelter. Other plants, usually forming upright bushes, are here compelled to bend before the strong winds; notable among these is the _Pituranthus aphyllus_, a leafless umbellifer. A plant of peculiar interest found among the many species of _Mesembrianthemum_ is the _M. rhopalophyllum_, which is remarkable for its highly-specialised window-leaves. “The plant grows embedded in the sand, nothing but the flat, slightly convex apex of each leaf being visible, and even that is covered with more or less sand according to locality. While the leaf itself is fresh green with a rather delicate skin, the exposed part is protected by a thick epidermis and cuticula, and possesses comparatively few stomata. It is through this portion, which has the functions of a window, the leaf receives its light, being thus illuminated from within. There are five to ten, or even more, leaves to each plant, but nothing appears at the surface except these windows; they peep out of the sand like the eyes of the sand-lizard or sand-vipers, which often hide themselves in a similar way.”[9] It is very curious to see the short flowers of these plants in the spring, for they grow, apparently, straight out of the sand. Only on investigation are the leaves and stem discovered. The leaves are club-shaped. Nature has evidently chosen this underground mode of existence for the plant in order to protect it against the herbivorous animals. These interesting plants are found only in Africa.