The Sultanate of Bornu

IV

Climatically, as well as geographically, Bornu belongs completely to the tropic zone; although cut off from the warmth of the Equator, its average temperature throughout the year of 29° to 30° centigrade makes it not only one of the hottest countries in Africa, but even of the whole world.[118] Though the climate of Bornu may on the whole be called regular, considerable fluctuations in temperature nevertheless take place, as is proved by the records of the last sixty years.

Of all the travellers who have spent any length of time in Bornu, the only observations that extend over a detailed period are those of Barth and Nachtigal; moreover, those of later travellers, which embrace a few months at the most, in the main and on the whole, in so far as they are not of small value, confirm the former results. Barth’s observations have the advantage of extending over several years, of embracing all parts of the country which he personally visited, and of having been manifestly taken at places whose situation could not influence the result one way or other. But their reliability is somewhat prejudiced by the fact that the necessary thermometrical readings are sometimes discontinued for weeks at a time, and were resumed on odd days at quite different times. These irregularities happen to be of especial importance in the thermometrical readings, which were taken after midday or during the afternoon, when according to experience quite considerable increases of temperature may occur in a short time. Owing to the fact that the traveller, especially at the beginning of his journey, was not always in a position to be able to take observations during the hottest part of the day, many high maximum temperatures no doubt escaped him. Barth himself was well aware of the insufficiency of his data, for he refers to them throughout only as ‘Fragments of a Meteorological Register’.

Nachtigal’s observations are extraordinarily conscientious and arranged with greater regularity and include also barometrical readings. But they extend, as far as Bornu is concerned, only over seven months and omit precisely the period when the highest temperatures occur. Moreover, the place where the observations were taken, viz. the court-yard of Nachtigal’s house in Kuka, was such that it must have influenced at any rate the thermometrical readings. Inside the walls of the town, daily baking in the sun, the nightly radiation from the soil does not nearly reach the same intensity as in the open plain; this is strikingly apparent in Nachtigal’s thermometrical readings. There is an absence throughout the winter months of the low temperatures, shortly before or after sunrise, which have struck every one travelling in Bornu at this season.[119] Moreover it is not to be forgotten that the shade-tree, under which Nachtigal took his observations, influenced the result both of the maximum and minimum readings.[120]

The table given below makes it apparent that April, with an average temperature of 34° centigrade, is the hottest month of the year and December the coldest; further, that the chief rainy months, July, August, and September, show the least fluctuations in daily temperature, while the coolest months, November, December, and January, show the greatest. The reasons are not far to seek, they depend on the position of the sun together with the degree of intensity of its rays resulting from its position. At the end of March the sun approaches its zenith for the first time—i.e. as regards Central Bornu—the atmosphere begins to be saturated with moisture and this lessens the fall of temperature at night, which becomes still less marked in April, in which month prevails the most oppressive heat, not yet mitigated by the rains.[121] The first tornadoes now set in, and become more and more frequent, while their ever-increasing volume lessens the nightly fall of temperature, though it affects the daily temperature in the opposite direction, so that the daily fluctuation of temperature in July and August only reaches 9°. At the beginning of the month of October the tornadoes cease, and consequently there is an ever-increasing rise of temperature to correspond, which, however, very soon drops in the following months.

Naturally the conditions for the northern and southern parts of Bornu vary somewhat, and local circumstances may also cause quite considerable fluctuations of temperature. Thus I noticed at Idjege in Southern Bornu, at the beginning of October, that the granite masses thickly studded with trees, on the slopes of which the place lies, had the result of causing an unusual increase in heat, which close to the surface of the soil measured 51° centigrade in the shade. While the nights here were even oppressively hot, a few days later on the plain at Dissa, not far from Idjege, the thermometer only showed 10° centigrade in the morning before sunrise, and by so doing registered the lowest degree of temperature, whose fluctuations far exceeded 30°. In general the heat reaches its highest point about 2 p.m. and then only declines very slowly, so that even in the evening abnormally high temperatures may be registered,[122] in fact the interesting phenomenon may occasionally be observed of a higher temperature at sunset than at midday.[123] If one takes the yearly average temperature according to Barth’s and Nachtigal’s tables, one cannot but notice that Nachtigal’s tables leave out of consideration just the hottest months. Having regard to this circumstance, one may reckon without much inaccuracy the yearly average temperature at from 29° to 30° centigrade.[124]

With regard to the second most important factor in the climate, viz. the winds, there exist no such detailed observations as with regard to the temperature; still the facts communicated on this subject by Nachtigal and recent French explorers, especially Foureau,[125] are sufficient to show that just as the atmospheric pressure is extremely regular so likewise are the winds. During the greatest part of the year, under the influence of the north-east trade-wind, north-easterly or easterly winds predominate, but south of 12° north latitude, where the wind comes mostly from the south with a decided inclination towards the south-east,[126] it is less constant, a fact which Foureau attributes to the counter-influence of the south-east trade-wind which reaches as far as here.[127] According to the universal verdict of all observers, easterly and north-easterly winds predominate especially in the dry weather, while in the rains, especially in July and August, westerly winds gain the upper hand, only to surrender their predominance to the easterly winds in October.

Views as to the daily fluctuation in the strength and direction of the wind appear to vary. Unfortunately Nachtigal’s tables[128] do not inform us whether observations with regard to the wind were taken also at night-time. The French naval officer Audoin, who personally took observations of this sort on Lake Chad, where the conduct of the watery plain is bound to give indications conformable to every movement of the wind, lays stress on the predominance of the north-east wind, especially from 11 p.m. to 9 a.m., while it is replaced by the south-west wind for the rest of the day.[129] The north-east trade-wind brings with it from the Sahara a great volume of dust, which often renders the atmosphere so opaque that the sun only appears through it like a dark-red disk. This phenomenon, which causes a peculiarly oppressive sensation,[130] is known throughout the whole of Western Tropical Africa under the name of Harmattan, but is especially characteristic of the Central Sudan.

Apart from the violent atmospheric disturbances which the tropical thunderstorms bring with them, the cyclones or tornadoes, coming sometimes from the south-east, sometimes from the north-east or south-west, especially during the times of the change in the wind, affect Bornu as well as the whole tropical district of the Western and Central Sudan.

In Bornu, where over wide stretches of country the weakening effect of dense forests is lacking, they attain an unparalleled violence. They give notice from afar of their arrival by thick clouds and whirling dust, and sweep everything off the earth that has not been made trim and taut. Sometimes cornfields which have been overtaken by them look as if a roller had passed over them. During the autumn of 1903 the roofs of the houses at Dikoa were blown off by a violent tornado. In general the cyclones are not preceded by discharges of electricity, but there are exceptions to this rule.

The tornadoes may be matched in violence by the thunderstorms which occur in Bornu. As is often the case in the tropics, they are heralded beforehand by the discharge of a large amount of electricity, a phenomenon which it is especially fine to observe at night, when the lightning flashes following each other uninterruptedly render it possible to read a book.[131]

Whilst on the subject of hydrometry, the question of cloud formation has next to be considered. The sky in Bornu, quite apart from the Harmattan, is very seldom quite clear; it is only in winter that there may be several successive days free from clouds; at other times ‘cirrus’ clouds at any rate are perceptible. The most wonderful cloud formations can be observed at the transition period shortly before the bursting of a thunderstorm. The results are analogous to those prevailing in Europe under similar circumstances; only in the Central Sudan the ‘cumulus’ formations differ in being grander, and they discharge themselves more quickly.

Fogs occur, but they are chiefly confined to the cooler parts of the year, and usually, as in northern latitudes, are connected with the presence of swampy districts, such as the damp low-lying shores of Chad. Besides it would be difficult, especially in the cooler morning hours, to distinguish sharply between fog and Harmattan.

Bornu lies exactly in the zone of the tropical summer rains, whose northerly boundary, naturally not to be sharply defined, coincides roughly with the fifteenth parallel of latitude, and thus includes also the most southerly part of the Sahara.[132] The moisture that falls there is only in the form of dew and rain. The mountains which border the country are not high enough to favour the formation of hail, which, however, is often enough to be seen in the neighbouring highlands of Central Adamawa and the grass-lands of the Kameruns that lie to the south of them. Dew appears—though only seldom—chiefly in September, October, and March; but then usually in profuse volume. Thus Denham in March and Barth in September experienced a quite extraordinarily heavy dew on the banks of Lake Chad, which they thought worthy of particular mention.[133]

The weather conditions accompanying the beginning or end of the rains usually occur with great regularity in Bornu. In this respect the country shows the typical Sudan climate, which is generally entirely without rain during the months of November, December, January, and February. The only noteworthy exception appears to be the actual borders of Chad. On the evening of the 22nd of January, an unusually cool day, and on the following morning, in the immediate vicinity of Chad, Foureau notes violent showers of rain, which were preceded in the afternoon by slight showers with some thunder and lightning.[134]

The rainfall is influenced in two different ways by the mountains on the southern border. Firstly, the volume of rain that falls here—though proper measurements of it have hitherto not been forthcoming—appears to be more intense than in the plains; and, secondly, the rains here set in earlier and do not end till later.[135] A greater or lesser distance from the Equator operates in a similar way. For the further south one goes, the longer is the duration of the rainy season and the greater the volume of the rainfall.

Apart from the above-mentioned exceptions, the first drops of rain do not fall in Bornu before the end of March. The downpour is heaviest in July and August. Though many of the tornadoes are extraordinarily severe and long-continued, yet the rain never lasts without intermission for a whole day or even a week, as it may do in the primaeval forest region of the Kameruns.[136]

In spite of the low rainfall as compared with that of Adamawa, which lies to the south of it, the climate of Bornu, except in the dry weather, thanks to its low-lying marshes, is distinctly unhealthy.[137] Besides the diseases, such as dysentery, which appear at all times of the year, malaria and its attendant evils are chiefly prevalent during the rainy and equinoctial seasons; Europeans especially are subject to it to an unusual extent, as are also the Arabs and Berbers accustomed to the healthy climate of the desert.[138] But even the natives are not entirely exempt from such diseases, which may assume the form of devastating epidemics.[139] The only part free from fever seems to be the uninhabited belt of marshy vegetation round Lake Chad, because infection from man to man is here impossible, although there are clouds of mosquitoes ready to convey the germs of the disease. On the same grounds the larger towns, which scorn all sanitary regulations, are the worst centres of disease. The irritant microbe which lives in the anopheles mosquito is paralysed at a temperature below 17° centigrade, and consequently dies during the cold nights of the dry weather, in the event of its host not spending the night in the warmth of a house.

The rainy season in Bornu is dreaded by the Berbers or Tripoli Arabs not only on account of the danger to their own health, but the condition also of the pack-camels bred in the Sahara is influenced very unfavourably by it, in fact it sometimes causes great mortality amongst them, so that the caravans, whenever they can, leave the country at the beginning of the damp weather.[140] It is not yet certain whether the camels fall victims to the same disease from which the animals bred in Bornu, horses and especially oxen, have to suffer. Inquiries into the question of whether it is spread in the form of a contagious disease like trypanosomiasis—the disease whose germ is conveyed by the tse-tse fly—have not yet been published, but at any rate myriads of flies belonging to the ‘Glossina’ species are to be found in the neighbourhood of the water-courses fringed with trees and bushes.

It is obvious that the moist heat of the rainy season is favourable to the growth of all kinds of sickness. Besides venereal disorders, malignant eye-diseases are very common, and, owing to the indolence of the natives, find every chance of being spread abroad; leprosy is by no means unknown.[141] One of the commonest evils is that caused by the guinea-worm, a skin-disease which, though not dangerous, is protracted; the worm enters the body through the use of unboiled water from puddles, water-courses, and even from wells, and almost every native has been attacked by it at some time during his life.[142] Cleanliness and the scrupulous observance of simple rules of health, including especially regular bodily exercise, afford, however, far-reaching protection against all these diseases, not excluding malaria itself, so that at any rate Europeans can secure themselves in some degree against sickness. All these districts are at all events far from being so unhealthy as the region of the West African primaeval forest, where the germ-destroying effect of the sun’s rays seldom penetrates.

V

The flora of Bornu corresponds exactly to the geological formation and climatic conditions of the country.[143] The usual appearance of the country is that of a tree-covered steppe, which extends south of the border-line of the regular summer rains over the vast plains of the interior of Africa from somewhat north of 8° of north latitude, from Senegal to Cape Guardafui, east of the great Central African lake and reaching southwards as far as South-East Africa. The character of this steppe is dependent on the predominance of deciduous plants, mostly belonging to the order of Leguminosae, and of many thorny trees and bushes, which very gradually give way on the borders of the country, according to local conditions, to representatives of the flora of the desert, of the damp tropical uplands or of the primaeval forest district, or else are found intermingled with them. Whilst Bornu shows in the north over a wide extent somewhat more luxuriant examples of species belonging entirely to the flora of the desert, on its own side also it spreads plants peculiar to itself pretty far into the south of the Sahara, but it lacks representatives of the above-mentioned grass-lands and primaeval forest flora owing to the predominance of evergreen trees and the appearance of epiphytic vegetation. Nowhere in Bornu can one find the dark-green forests with their hot-house humidity and tree-loving ferns, orchids,[144] and begonias, with pandanacea and different kinds of climbing calamus, with raphia- and oil-palms, which in dense lines edge the water-courses of the grass-lands lying not much further south. Of plants which are peculiar to such districts, the banana is only to be found at one place in the country, and that curiously enough is at Zinder, in the north-west corner of the country, whither it must evidently have been introduced from outside.[145] The raphia-palm, Raphia vinifera, and different varieties of paw-paw[146] first appear on the southern edge of the Mandara mountains, which lie scattered to the south of the tenth parallel of north latitude, and only one variety of Ceiba pentandra, which is indeed stunted enough in comparison with the specimens of giant Ceiba (Bombax) of the West African primaeval forest, is to be found here and there in the neighbourhood of the water-courses. There are indeed the trees of the Ceiba species, which, in contradistinction to the evergreens, shed their leaves in the dry weather—even in the primaeval forest. It appears rather strange that none of this kind of vegetation occurs along the course of the Lower Shari, which is always full of water, although it is plentifully represented at the sources of that river, especially the Gribingi,[147] and although it extends for a short distance down-stream close to the banks. The reason of this phenomenon may perhaps be sought for in the fact that the long and intensive dry weather of Bornu, and also of the Lower Shari country, is not favourable to this kind of vegetation. This is analogous to the similar phenomenon on the Upper Nile, where the plant formation of the hot damp countries where the river rises extends through districts which get drier and drier as one proceeds northwards, but cannot advance at all after the latitude of Khartum.

The sole or at any rate predominant landscape as regards Bornu, so far as it depends on the flora, is just this tree-studded steppe.[148] Even the trees are in unison with this steppe; if they do not belong to the prevailing species of acacia, they are at any rate of a habit in accordance with them. They are in general low, stunted and twisted, with deep roots and wide-spreading crowns, not higher than the trunk of a twenty-year-old oak sapling; only along the water-courses and where a deep layer of ‘humus’ soil exists do they reach a more considerable height, but even in the most favourable spots they do not much exceed 25 metres. The density with which the trees are planted depends also on the condition of the soil. Generally the trees stand in high steppe-grass at such long intervals that their crowns hardly touch, then the landscape reminds one of the extensive fruit-tree plantations of the north. The better the soil is, the closer stand the trees and thus form dense wide-spreading forests, often tangled with creepers, as for example in the riverain district of the Lower Shari from Karnak to Lake Chad.[149] In other places, especially on the granite slopes of the hills that jut out into the Bornu plain, the trees occur so far apart, that the landscape comes to show a great similarity with the slopes of the Sierra Nevada covered with sparse ilex trees which dip down to the Rio Genil in Southern Spain. In fact, where the true tropical trees, such as the palm and fig species, or the strange-looking ‘kuka’ (Adansonia) are wanting, the general impression of the flora is quite that of Northern Europe. Often, especially in winter when the ground is covered with fallen leaves, one can find places that at once recall the tree-bordered river valleys of the low-lying plains of North Germany in autumn. Localities which give a regularly tropical impression are at all events not in the majority, and the inspired descriptions of tropical luxuriance which Nachtigal gives on his first acquaintance with these parts, originated, as he himself has to admit, from the impression of dissimilarity between the Chad countries and the Sahara through which he had just struggled.[150]

By far the largest number of characteristic trees and bushes are naturally of such a stamp as are suited to the conditions of the country. The arrangements designed for the preservation of species are the thorny spikes for defence against annihilation by things that feed on them or for protection against drought during the winter months. Most of the trees shed their leaves in the dry weather, but those that do not, possess a quantity of thick leathery foliage or fine feathery leaves, succulent twigs, tendrils with tough outer fibre or thick cork-like bark. On the shea-butter trees, Butyrospermum Parkii, and the ilia-acacia, Burkea africana, and especially on the timber found in Southern Bornu, this thick cork-bark is to be observed, serving at the same time as a protection against the ‘bush’ fires.[151]

Soon after the beginning of the dry weather the high grass is quite dry, and affords ample material for the ‘bush’ fires that now commence. The trees and bushes, sticking out of the burnt, ash-covered soil with their bark all charred, offer then a melancholy spectacle. This may make them appear as if quite dead, but as a matter of fact the bark, of which only the outer layers have been burnt, has been able to protect the sap so well, that just before the beginning of the first rains tree and bush put forth fresh leaves and twigs or even stand dressed in full bloom.[152] About the beginning of January the Leguminosae begin one by one to bloom, and shortly afterwards the other trees and shrubs follow suit, so that the ‘bush’ is soon pervaded with an overpowering perfume.

A few species of trees form a remarkable exception, for it is just during the rains that they are leafless and seemingly dead, yet as soon as the rains are over they put forth new leaves and reach their greatest luxuriance in the middle of the dry weather.

After the first tornadoes the ash-covered earth begins to cover itself with a thick green turf, which gives the landscape a park-like appearance, and from it spring in a few days great quantities of variegated Ranunculaceae and lilies, followed soon afterwards by the flowers of such trees and shrubs as have not already come into bloom. When the flowers come into view, the season corresponds somewhat to the spring-time of Central Europe, and a similar state of things continues for the following months; by June or July the leaves are all fully out, and in October, at the end of the tornado season, the latest fruits have ripened. Among the fruit-bearing trees that grow wild are some that are made use of by the natives; as regards the greater part of those mentioned by European travellers as being useful, there are very various reports. Barth, who seems to be by no means dogmatic, praises them for the most part, but Denham expresses himself less favourably, and the greater part of this traveller’s observations come pretty near the truth.[153] At all events the really pleasant-tasting fruits are quite rare in the ‘bush’.

The flora of Northern Bornu is also strongly influenced by the Sahara, which pushes forward representatives of its own here and there far beyond its borders. In addition to the different species of thorny acacia, similar to each other in habitat, which after reaching a certain age generally have umbrella-shaped crowns, and which are so generally characteristic of all the sterile districts of Africa, the two regions have quite a number of plants in common.[154] The two most striking, which one meets almost everywhere, are the Zizyphus species and the oschar, Calotropis procera (called by Barth Asclepias gigantea). The wide distribution of the Zizyphus species is explained by its suitability to all kinds of soil and the usefulness to mankind of its fruit, which is mealy tasting and slightly sweet, and for the sake of its branches to form thornhedges as a protection against beasts of prey. The Zizyphus is found northwards as far as the Mediterranean countries[155] and southwards as far as the boundaries of the Sudan climate. The two varieties principally met with in Bornu are those called by the natives ‘Kurna’ and ‘Magalia’, Zizyphus Jujuba and Zizyphus spina Christi respectively. The hardy ‘Magalia’ may take the form of magnificent shade-trees, especially in sandy soil, and constitute in uninhabited places thick thorny copses, which lead one to conclude almost with certainty on the presence of former settlements. The ‘Oschar’, far the tallest of all the Asclepiadae,[156] owes its wide distribution to the seeds, provided with silky floating fluff, distributed by its fruit, which is shaped like a small bladder and is larger than a man’s fist. These plants, which are in their fullest foliage towards the end of the dry weather, are to be found all over the Sahara[157] in favourable localities, and form on the sand-dunes of the south-west shore of Chad wide-spreading bushes,[158] whose grey-green leaves give to the landscape an impression of uniformity and melancholy, and extend from here even as far as Lagos.[159]

Of widely distributed plants belonging to the two regions in common, one of the most remarkable is the dum-palm, Crucifera thebaica, the sole representative of its genus, whose trunk is divided into several branches. They prefer a soil that attracts the surface water, and are to be found from the oases of the Central Sahara to far into Adamawa—though here indeed only very scattered; some splendid examples flourish especially at Ngornu, on the shore of Lake Chad. South of this region it is very rare. According to Barth the fruit may be used in large quantities for food,[160] but on the other hand the same traveller points out that the low-growing dum-bushes are a hindrance to agriculture.[161] In fact, between Kukawa and Ngornu one finds wide stretches so thickly studded with the young plants of this palm which it is so difficult to eradicate, that one is reminded of the plains of the Mediterranean littoral overgrown with ‘chamaerops’.[162]

The date-palm also, the most characteristic tree of the Sahara, is to be found dispersed in single examples all over Bornu, and specimens transplanted by man may even be seen in the middle of Adamawa. But it is seldom or never that it bears fruit in Bornu; the summer rains do not suit it, any more than they do the camel, and it is a proof of the desert character of certain of the sandy valleys of the neighbouring country of Kanem, that the date-palm flourishes there in full luxuriance and bears abundant fruit.[163]

Belonging likewise to both regions, but confined within narrower limits and generally not extending farther south than the latitude of Kukawa, there are certain plants found in Northern Bornu which are partly used for the production of salt. The most striking of these is the peculiar ‘tundub’, Capparis aphylla (sodata),[164] found in the same parts as the dum-palm, the ‘ethel’, Tamarix articulata,[165] the ‘retam’, Retama spec—according to Barth Spartium junceum[166]—the Salvadora persica, and the Asclepias leptadenia pyrotechnica.[167] Of these only the ‘tundub’ and the ‘retam’ are to be found widely distributed in Bornu. The ‘tundub’ is of importance in that the ashes obtained from it furnish the natives with salt.[168] As a salt-loving plant it is only to be found on soil impregnated with natron, and becomes rarer as the percentage of the mineral necessary for it to thrive decreases. It does not seem to reach farther south than Kukawa. The ‘retam’, one of the European species of Spartium or Ulex, similar to the Papilionaceae, forms on the sand-dunes south of Maduari thick bushes taller than a man, which give to the places where they are found quite a northern appearance owing to its genesta-like exterior.

Other kinds of trees and shrubs which belong without any doubt to the Sudan, have nevertheless in favourable localities extended their area of distribution far into the Sahara. Among these is the ‘hadjlidj’, Balanites aegyptiaca, whose name, like that of the Crucifera thebaica, indicates a very wide distribution; with its dark-green hanging boughs it presents a very striking appearance. Its fruit, called ‘bito’ in Kanuri, plays, according to Barth, an important part as an article of diet among the natives.[169]

It is much more difficult to define the area of distribution of the acacias than of the other well-known species of trees, because they resemble each other very much in all countries, and because it is only very insufficiently established to what species they belong owing to their great multiplicity of form. The definite classification of the various species of acacia found in these regions, which is impossible without the possession of an ample collection of material—at present not yet forthcoming—would be a task well worthy of the gratitude of botanists. But the classification is the more difficult in that each of the numerous books of travel, while multiplying the names given by the natives to these trees, apparently assign them to different species. It is always possible that the natives, on whom botanical peculiarities are naturally lost, may assign the same name to similar species. One may therefore assume with certainty that the Arabic word ‘talha’ is a term applied to all species of acacia that exude gum arabic.[170] By ‘talha’ are especially meant the Acacia ferruginea common all over Bornu with its little unmistakable reddish-brown trunk and branches and its dark golden blossoms,[171] the Acacia stenocarpa,[172] and the Acacia tortilis,[173] widely distributed in North Africa. All these species, whose ball-shaped little blossoms make their appearance during the first months of the year, diffuse at that time an extraordinarily strong perfume reminding one of the violet or the heliotrope. To the finest species, which assume with especial clearness the umbrella-like form, belong the Acacia arabica, found far from here even in Aïr, and especially the ‘gawo’, Acacia albida. The ‘gawo’[174] is especially remarkable for this reason, in that it strikes one from a distance by the complete bareness of its greyish-white branches during the rains; it is not till October that it puts on its feathery leaves of greenish-grey and its blossoms that remind one of willow-catkins.[175] To be found all over Bornu and stretching far afield towards Adamawa, it reaches giant dimensions on the banks, rich in ‘humus’, of the River Yedseram, south of Bama.

The steppe-forest of Northern and Central Bornu[176] is composed somewhat as follows. Scattered among the acacias, which predominate, are the above-mentioned species of trees—to which may be added in Central Bornu the ‘dschochan’, Diospyrus mespiliformis—which, however, form isolated patches in the acacia forest whenever the condition of the soil is suitable. The commonest of these is the ‘hadjlidj’ (Balanites). Next to this the most frequent is the ‘Kargu’ or ‘Kalgo’, Bauhinia reticulata, belonging to the order of Leguminosae, a shrub found as far as Munio and Zinder,[177] which, like the Mimosa pudica, is remarkable for rattling at night its large leaves shaped like an inverted heart. This shrub appears mostly in the form of brushwood, prefers a sandy soil, and on the summit of the dunes along the shores of Chad replaces in some parts the Zizyphus and the Calotropis procera, with whom it also enjoys a joint tenancy. It is likewise as a brushwood shrub that the Gardenia Thunbergia forms sparse bushes, whose thorny branches are covered in the spring-time with big snow-white blossoms, which first open towards evening and then diffuse a strong penetrating perfume. The branches of these trees and shrubs are often intertwined with the parasitic loranthus, whose rather large honeysuckle-like trumpet-shaped flowers probably misled Barth and made him mistake them for orchids.[178] The loranthus with its fleshy grey-green leaves and hanging tendrils often forms great bushes, whose masses of foliage may quite obscure the green of the tree it clings to. Many other creepers attain such luxuriance that the tree they overgrow completely disappears beneath their masses. One of the most striking is the sappy cactus-like ‘digessa’, Cissus quadrangularis, in which the small leaves are inconspicuous as compared with the evergreen and peculiar four-edged tendrils. According to Rohlfs, this plant, which is widely distributed all over the country, is one of those from which the natives prepare their arrow-poison.[179] Besides the Cissus there is a kind of ‘luffa’ which is worthy of notice; its fungus-like fruit on its withered tendrils attracts the attention of the traveller in the dry weather from a long distance.

The high ant-hills in the ‘bush’ are regularly carpeted with Capparidae such as the Cadaba farinosa and Capparis tomentosa. The latter especially affords a peculiar sight in winter and early spring, when its thorny semi-creeper-like tendrils are in bloom. The blossoms, to which are attached numerous long pollen-vessels, attract—as do the acacias—through their strong honeysuckle-like perfume the whole flower-loving insect world and the metallic-coloured honey-birds.

Many trees in the ‘bush’, and especially those which prefer marshy places or the banks of streams, are inclined to isolate themselves and so form splendid clumps, solitary and circular, that give the landscape quite a park-like appearance. To this category belongs especially the tamarind, Tamarindus indica—in spite of its name indigenous to Africa—which does not shed its dark-green feathery leaves even in the dry weather and puts forth its orchid-shaped flowers in the winter. Its fruit serves many medicinal purposes and when pounded in water makes a refreshing beverage. Even commoner than the tamarind are the various species of evergreen fig which Bornu harbours, each in individual isolation; such isolation is grounded in their very nature. Though of great variety in the form and size of their leaves, they all show in their habits the same characteristics. Similar to its Indian relative, the banyan, in the early stages of its growth it takes the form of a semi-parasitic creeper, which shows a distinctly astonishing inclination towards a spread both of roots and branches. Soon after it has surrounded the tree that serves it as host with a many-meshed net, the latter perishes; the inextricable tangle of wood forms a single trunk, which, as branch and bough keep on sending out new roots, finally supports of itself the giant arbour-like roof of foliage, composed of the countless roots both thick and thin that in their turn struggle earthwards. The milk-like sap of all these species exhibits in a dried-up condition more or less of the elastic properties of caoutchouc; the fruit of some species are edible. One large species, known in Bornu as ‘ngabore’,[180] with poplar-like blackish-green leaves, reaches especially at Ulugo and other places on the south shore of Chad a height of over twenty metres and surpasses all other shade-trees owing to its density of foliage. Owing to its dark colouring it stands out sharply defined from everything else during the dry weather and forms a striking contrast to the uniform muddy grey of the villages. Of much less compact shape is the equally widely distributed Bignoniaceae, Kigelia pinnata, which is found as far as Kanem,[181] and to which the much-travelled Hausas have assigned the name of ‘nono-n-giwa’ (that is to say, elephant’s udders) on account of its sausage-like fruit, which is over a foot long and hangs from a long stalk. It is very commonly found in the middle of the towns. The walnut-like leaf of this tree also lasts through the dry weather, during which appear its straggling dark-red clusters of blossom.

The ‘bush’ in Northern and Central Bornu differs in one respect from that of the southernly districts, in that the grasses which cover the soil do not there reach the same great height; in sandy places the low-growing prickly grasses called ‘ngibbi’, Cenchrus echinatus and Pennisetum dichotomum, predominate, of whose notorious seed-grains Denham remarks: ‘These prickles may be considered one of the pests of the country.’[182] The unpleasant burr-like adhesive seed-grains of these grasses cling fast everywhere and are a regular plague both to man and beast—in fact, the latter’s hair is often thickly matted with them. Owing to the easy way in which these noxious weeds are spread, they at present flourish all over the Sudan, wherever they are not kept under by other plants. It is astonishing how the Bornu horses are able to eat the Pennisetum dichotomum without any ill results, nay, Barth goes so far as to say that they will not thrive without it.[183]

The Graminae flora are always predominant also in the undergrowth, for the herbaceous flowering plants only make their presence felt during the spring. Frequently the often magnificent flowers appear long before the leaves, and are either stalkless like those of a large Zingiberaceae, or else push their heads only a little above the surface of the soil like those of the strange Amorphophallus species and other Araceae. To one of these families perhaps belongs the bulbous plant eaten by the natives and mentioned both by Barth and Rohlfs, under the name of ‘Katakirri’ or ‘Gadagér’, as being found in Southern Bornu.[184]

In the districts in which the ‘bush’ consists chiefly of elements which belong also to the Southern Sahara, it experiences in places interruptions of quite foreign appearance, namely, from the flora of the shores of Lake Chad and from the desolate ‘firki’ flats.

Peculiar to the shores of Chad is the total absence of trees. This is only to be explained by the great irregularity of the water-level of the lake, which must be extremely unsuitable for steady yearly growth: during the long-enduring inundations, which put everything under water a yard deep for months at a time, those trees are bound to decay which cannot thrive except in a position which is normally dry. On the other hand, trees whose roots demand a copious supply of water, suffer from a year-long drought and find no compensation in the downpour, abundant as it is, of the short rainy season for the absence of water springing from below.

The places where trees grow—especially on the west and south shores of Lake Chad—mark the boundary of a zone of marsh vegetation poor in species but nevertheless interesting. Besides the high grasses and the Mimosa pudica, which is ubiquitous wherever there is water, there is usually nothing but the papyrus and the ‘ambatsch’ or ‘marria’,[185] Aeschynomene (Herminiera) elaphroxylon, both of them plants which, owing to their simultaneous appearance in the ‘sudd’ of the Upper Nile, seem to point to an earlier connexion at some time between the two districts. The papyrus, which is also found in the brackish lakes of the Munio country,[186] reaches in the swampy thickets of Chad the considerable height of four metres, but it is overtopped by the ‘ambatsch’. As its name (elaphroxylon) indicates, the latter is of unusually rapid growth—in fact, one gets the impression that the stem of this giant plant, which is as straight as an arrow and often as thick as a man’s leg, reaches its full height inside of a single year. As soon as the water recedes from any place for any length of time the ‘ambatsch’ dies, and then the shore is covered far and wide with the dead trunks overlaid with green creeping plants. The wood, when quite dry, has an elder-like pith, but is nevertheless comparatively durable and extraordinarily light—a log as thick as a man’s leg, and some seven metres long, hardly exceeds one kilogram in weight—and is put to various uses by the inhabitants of the shores and islands of Lake Chad. The ‘ambatsch’ as well as the papyrus, standing in some places a yard deep in water, is generally thickly covered with the tendrils of a luxuriant kind of Ipomoea, whose big purple trumpet-shaped flowers, mingled with the golden-yellow butterfly blossoms of the ‘ambatsch’, at any rate enliven what is otherwise a monotonous vegetation.[187]