Another notable type of vegetation is what may be termed the Namib-Karoo. It is chiefly developed in the west, extending from South West Africa, through Namaqualand to the coastal ranges which form the boundary of the Cape Flora. It extends eastwards to axe standing on its head. In the west the junction with the Cape Flora is usually sharp but in the east the boundaries are much less definite. In places the Karoo approaches true desert but over most of its area it is best described as semi-desert. Succulents form an important element, especially in the west and give this type of vegetation a character unique in the Southern Hemisphere. The Karoo Flora is adapted to a low and erratic rainfall. With increasing altitude and the likelihood of severe frost during the winter, succulents disappear and are replaced by sparse, low bush with grasses occupying the ground between bushes after a rainy period. The past history of this most interesting arid type of vegetation is obscure. There are no indications that it arose anywhere but in South Africa and there are no clues as to its age. It is adapted to life under arid conditions and probably arose in one or more of the dry periods in South Africa’s history. It is presumably younger than the Cape Flora for the striking discontinuities in distribution which are a feature of the latter, do not appear in it. Far too little is known about it to hazard a guess as to its age though it is almost certainly older than the floras lying to the north.