forests except on the Malabar coast, in Ceylon, and around the Caribbean seaboard, whereas in North Africa the dûm palm (hyphæne thebaica) and the deleb (borassus flabelliformis), as well as the date (phænix dactylifera) cover extensive tracts in the oases of the northern Sahara. Compared with the number of its species, the Nigretian flora possesses many trees with an abnormal development of stem, leaf, and fruits. The baobab is noted for the enormous size of its trunk, while the kigelia and some other bignoniaceæ have fruits two feet long, and the eusete, a variety of the musaceæ, displays the largest foliage in the entire vegetable kingdom.
The Kalahari flora, south of the tropical domain, resembles that of the Sahara, except that it forms no oases, nor are the few watered tracts anywhere shaded by palms. This flora is distinguished by its thorny acacias and mimosas, and, like that of Northern Nigretia, it abounds in graminaceous species. On its northern margin some almost rainless districts grow the welwitschia, a remarkable plant, so flush with the ground as often to escape the notice of travellers. Burrowing downwards in the form of a reversed cone, it displays above ground nothing but a rough surface over a yard long, throwing off right and left two cotyledons of a leathery appearance, and occasionally exceeding 16 feet in length after a growth of one hundred years.
On the east coast of Africa, the transition between the vegetable zones is more gradual than on the opposite side, where the tropical domain is abruptly limited by the Kalahari desert. Along the Indian Ocean the change takes place imperceptibly from north to south through the Limpopo basin and Natal. On this seaboard, which is skirted by the warm Mozambique stream, the southern limit of the palm lies 16 degrees lower down than on the Atlantic coast. But on the whole the vegetation south of the Orange River is clearly distinguished from that of the rest of the continent. Although the rainfall is limited and the geological formations far from varied, the Cape flora, consisting chiefly of grasses, shrubs, and bushes, is altogether unique for the multitude of its intermingled species. In this respect it is unrivalled even by the richest European countries. Nowhere else do the mountain slopes present more vegetable forms disposed in belts sharply separated from each other by the several zones of altitude. It may be asked whether this Cape flora is not a survival from far more extensive lands engulfed in the sea, most of whose vegetation has found a refuge in the relatively limited tract bounded northwards by the basin of the Orange River. In the same way the island of Madagascar appears to have preserved a great part of the flora of the vanished "Lemurian" continent. It still possesses over forty vegetable families peculiar to itself.The appearance of Europeans and Semites has been accompanied by the introduction of many new species, which in several districts have displaced and even exterminated the indigenous forms. Elsewhere the range of certain plants appears to have been modified even without the intervention of man. Thus the papyrus, which three thousand years ago was characteristic of the Egyptian Nile, is now, according to Schweiufurth, found only on the Upper Nile near the equator.