Of the Upper Nile: Its Botany Compared with That of Similar Obstruc- Tions in Bengal and American Waters

The 'Sadd' of the Upper Nile: its Botany compared with that of similar Obstruc- tions in Bengal and American waters.

C. W. HOPE.

INTRODUCTORY. HE Cataracts on the Nile are well-known obstacles to T navigation between its mouth and the Soudan, but they are beginning to yield to the attacks of modern engineers, who are throwing dams across the river, and providing side channels through which navigation will be carried on by means of locks. These cataracts are caused by barriers of granite rock which cross the bed of the river. But it is not so well known that an almost more serious obstruction to navigation is caused by the accumulation of a few species of plants floating in the Bahr-al-Jebel, or Mountain Nile, beginning about 435 miles south of Khartum, and extending thence .southwards for about 350 miles; and that this accumulation also seriously reduces the flow of water northwards to the Lower Soudan and Egypt. The great Equatorial Lakes store the rainfall of vast catchment basins, and so regulate its off-flow northwards by means of the Mountain Nile ; but this function is greatly neutralized by the vegetable accumulation which begins 715 miles northward, in a comparatively flat country, and which reduces the velocity of the current, and also causes the water of the river to spill right and left over the country and go to waste in shallow lakes and lagoons, where it is subject to evaporation to a serious extent.

[Annul, of Botany, Vol. XVI. No. LXJ1I. September, igog.]

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 496 Hope.—The 'Sadd' of the Upper Nile. Previous to 1863 both the Bahr-al-Jebel, or Kir, and its eastern branch, the Bahr-al-Zaraf, had been navigable, but in March of that year the Nile, below their junction with the waters coming in from the west and northward—thence northwards called the White Nile, or Bahr-al-Abiad—was found to be blocked by ' an accumulation of vegetable flotsam, and it cost the crew of the Tinne" Expedition two days' hard labour to take their vessel through a channel which had been partially cleared by their predecessors. The obstruction rapidly increased, and thirty vessels had to be employed for five weeks to open a permanent passage. Matters went from bad to worse, till, in 1874, Ismael Ayub Pasha cleared the main route by the White Nile and the Kir. But in 1878 ' the White Nile rose to an unusual height, and enormous quantities of vegetable debris were carried off by the current. A formation of bars (blocks) on an unprecedented scale was the result, and communication between the Upper and Lower Nile was not restored until 1880.' If the Kir and the White Nile, with their comparatively strong current, were thu9 obstructed, it was natural that the more sluggish Bahr-al- Ghazal should contain more extensive though less compact accumulations. ' In 1881 Gessi Pasha spent three and a half months on a part of the voyage westward usually performed in five hours, and lost half of his men by starvation. Between the mouths of the Kir and the Bahr-al-'Arab there were twenty distinct dams.' The above information has been found in the' Encyclopaedia Britannica'; but—fully to realize what the Nile'Sadd'is—it i3 necessary to read the Report by Sir William Garstin, K.C.M.G., as to Irrigation projects on the Upper Nile, &c, accompanying a despatch by Lord Cromer, His Majesty's Agent and Consul General at Cairo, which was published as a Blue Book in July, 1901. In Part II of his Report, 'Points for future Study,' we find a section ' The Sudd.' (The spelling of this word is various in these papers, and the pronunciation consequently uncertain; but it seems probable that ' Sudd' is a transliteration into English, and that the word ought to

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hopt—TJu 'Sadd' of the Upper Nile. • 497 be pronounced like the first syllable of ' sudden,' and therefore, to all but Britons, ' Sadd' would be the better guide.) Sir William Garstin says that his Report is the result of his observations made during three consecutive years. In 1900 he had ' the advantage of studying the actual process of its formation on the spot,' as he. was imprisoned for three days in the Gebel River, owing to the ' Sudd having burst in ' (from the side lakes and lagoons) ' and blocked the channel down- stream of the steamer.' ' In 1890—91 a reconnaissance survey of the Bahr-al-Gebel (or Jebel) from Lake No southwards to Gondokoro was finished ; and a map to the scale of 1 inch to 10 kilometres is given with Sir William Garstin's report: it shows very clearly the features of the river's course; the lakes and lagoons met with ; the positions of the ' Sadd ' blocks then found, and the nature of the swamps, whether papyrus or grass. The last block met with, the nineteenth, was just above the 400 kilometres point from Lake No, near Ghaba Shamb^, one of the Nile Posts of the Bahr-al-Ghazal Province. Papyrus swamps ceased at about'460 kilometres, and the plant does not seem to have been found south of about 520 kilometres. ' In the Bahr-al-Jebel,' says Sir William Garstin,' the main factors of the " Sadd " are—the papyrus, and the " um-soof" (or omm-soof) reeds. These two, with the earth adhering to their roots, form the real obstacle. Many of the smaller swimming plants, such as the Azolla, the Utricularia, and Ottelia, are mingled with the others; but they certainly do not play any important part in the formation of the obstacle. The ambatch, too, has been unjustly accused of assisting in forming the barrier. This is not the case. This plant does not grow in any great quantity in the vicinity of the Bahr-al- " Gebel, and its stem is so light and brittle that it would break when subjected to great pressure. ' On the Bahr-al-Ghazal, on the contrary, the sudd is chiefly composed of the swimming plants above mentioned. Their breeding places are Lake Ambadi and the other lakes to the south. The Ghazal sudd is much lighter in texture than that

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 498 Hope.— TIie 'Sadd' of the Upper Nile. of the Gebel, and is consequently much easier to remove. At the same time, even in the former river the sudd is at times dangerous, especially if it forms down-stream of a vessel, and if the latter has to work upon it from its up-stream end. The accident to Gessi Pasha's expedition in 1881 proves that even the Bahr-al-Ghazal sudd can be an impassable obstacle under such circumstances.' How these various plants come to be so massed, in the respective rivers, as to form the barrier called ' Sadd,' or ' Sudd,' is very graphically explained by Sir William Garstin ; but the account will not bear abridgement, and it must be read in the Report itself.

THE BOTANY OF THE ' SADD.' The mention, in Sir William Garstin's Report, of certain plants, as inhabitants of the swamps and lagoons of the Upper Nile and its branch the Giraffe Nile, and its tributary the Gazelle Nile, and as constitutional parts of the ' Sadd,' has led to an investigation of these plants from a botanical point of view, and the following are the identifications which have been made, and notes as to their characteristics. The Papyrus Plant. The Papyrus plant—Cyperus Papyrus, Linn.—was, in ancient times, widely cultivated in the Egyptian Delta, where it was used for various purposes, but especially in making a writing material; but it is now extinct in Lower Egypt, and it is believed that it was not indigenous there, but probably had been introduced from Nubia. A clump of it grows in the tank- house in the Royal Botanic Gardens, Kew, with many stems, some of which are 9-10 feet in height above the water, while others, also in flower, are only about 6 feet high. A very characteristic picture of a large clump, backed by a tall grass or reed, is to be found in the Gardeners' Chronicle for 1870, p. 314, which was taken from a photograph of the plant as it grew on the Anapo River in Sicily. The plant has been re- cently and authoritatively dealt with by Mr. C. B. Clarke, F.R. S.,

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of tlte Upper Nile. 499 in the ' Flora of Tropical Africa,' Part II, vol. viii. Mr. Clarke gives Cyperus Papyrus, described by Linnaeus in his ' Species Plantarum,' as the typical species, and names Cyperus syriacus of Parlatore (which grows on the Jordan) and Papyrus sicula, Parl., and P. antiquorum, Link, as synonyms; and he separates, but only as a variety, P. antiquorum, C. B. Clarke. He gives the habitats of the typical plant as Africa : Upper Guinea, Lower Guinea, South Central Africa, and the Mozambique District; and the habitats of his variety as, in Asia—Palestine; and in Africa—Nile Land, the White and Gazelle Niles, Mozambique, and Zanzibar. Mr. Clarke refers to an article by Mr. Thiselton-Dyer, in the Gardeners' Chronicle of January 16, 1875, p. 78. In that article Mr. (now Sir William) Thiselton-Dyer says: ' Probably few persons in this country are-prepared to regard the Papyrus as a European plant, yet it has long been known to occur in many parts of Sicily, and it is more than likely that it is from this source rather than from the East that the specimens in various botanic gardens have been ultimately derived.' Mr. Thiselton-Dyer quoted a description given in a previous number of the Gardeners' Chronicle (1870, p. 314) by E. O. Fenzi, of the Papyrus in the Anapo River, where it grows to the height of from 13 to 15 feet. Macgregor, in the Illustrated London News, April 24, 1869, describing the Papyrus on the waters of Merom, Syria, said:—' On this (morass) is a vast floating forest of Papyrus and cane, perfectly dark inside. I could never penetrate more than 3 feet. Many of the stalks of the Papyrus are as thick as my arm. The water percolates below and through the spongy mass, and there loses at least half its volume by absorption and evaporation. This impassable barrier is about a mile wide.' In the transactions of the Edinburgh Botanical Society, vol. x, 1868-69, will De found a very interesting and instructive paper of notes on the Botany and Agriculture of Malta and Sicily, by Dr. Hugh Cleghorn, late Conservator of Forests, Madras, who spent three months of the winter of 1867 and M m

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 500 Hope.—The 'Sadd' of the Upper Nile. 1868 in those islands. In February 1868 he visited Syracuse, but had not time to visit' the renowned station of Papyrus antiquorum, the celebrated fountain of Arethusa,' on an island close to the harbour. Dr. Cleghorn said: ' The Papyrus grows luxuriantly on the banks of the Cyane (see illustration in " Le Tour du Monde," 1866), amongst flags, reeds, and water plants. . . . There appears to be no other spot in Europe where this interesting plant flourishes in a-natural state. The' clumps are very thick, attaining a height of 15 to 18 feet It is supposed to have been sent from Egypt by Ptolemy Philadelphus to Hieronymus II, 250 B. C. . . . Paper is now prepared as a curiosity by Signor Politi in the same way' (as described by Pliny, Book xxi, Sect. 12). Afterwards, Dr. Cleghorn visited Palermo, and saw the locality where it is said the Papyrus formerly grew, now called the Papireto. ' The Papyrus of Sicily,' he said,' is not mentioned by Theophrastus, Dioscorides, Pliny, nor Ovid, nor even by Diodorus Siculus and Theocritus, who were Sicilians. The first notice of it is contained in a translation by Professor -Amari, quoted by Professor Parlatore, from the Arabic of Ibn Hankal, a learned Arab, who visited Palermo in the tenth century. The following is an extract: " Among these marshes (on the streams about Palermo) there is a bottom covered all with Papyrus, from which writing-paper is made. I had not believed that it grew anywhere on the earth except in Egypt, but here I have found it in Sicily. The greater part is twisted into ship cables, and the remainder serves to make paper for the Sultan, who, however, hardly gets as much as he requires. The place, now dry, and partially filled up, retains the name of Papireto.' Till 1591 it was a vast swamp, full of Papyrus! Mr. Thiselton-Dyer, in the paper quoted above, said that Bruce found the Papyrus at Lake Zana (Tsana) in Abyssinia, in 120 N. Lat. Lake Tsana, as we learn from Sir William Garstin's Report, lies at an altitude of 1,775 metres above sea- level, over 5,800 feet.

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 501

' Um-soo£' The other main factor in the composition of ' Sadd ' is, according to Sir William Garstin, the 'um-soof reed. That is the Arab name of the plant: the botanical name is, according to Dr. Georg Schweinfurth (the author of ' Beitrag zur Flora Aethiopiens,' Berlin 1867, and other works on the botany of the Nile Region), Vossia procera, a grass belonging to the tribe Rottboellieae. But, says Sir William Garstin, ' the sample of this grass sent to the British Museum was identified as Phragmitis communist The specimens of Vossia procera in the Kew Herbarium show a thick stem, with long and broad sheaths from the nodes which at first envelop the stem and make it appear thicker than it really is. It throws out roots from each node (or joint), which draw nourishment from the water in which it grows, and also from the mud should the stems lie prostrate, as probably they at first do. Schweinfurth, in the book presently to be quoted from as to ' Ambatch,' mentions Vossia procera as one of the plants which have a share in the formation of the floating ' Sadd' islands. This must be a comparatively new identification, for in the ' Treasury of Botany,' 1870, it is stated that Vossia cuspidata, a native of the West Indies, is the only species of the genus.

' Ambatch.' This plant, Herminitra elaphroxilon, Adanson, the only species of the genus, belongs to the order Leguminosae, and has ' thorny branches, abruptly pinnate leaves, and large orange-coloured flowers, succeeded by linear oblong com- pressed legumes, which become at length spirally twisted.1 Sir William Garstin, as has already been mentioned, says that this plant has been unjustly accused of assisting to form the ' Sadd ' in the Bahr-al-Jebel; that it docs not grow in any great quantity near that river; and that its stem is so light and brittle that it would break when subjected to pressure. But this is not the view Dr. Schweinfurth takes of it. In his M m a

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 502 Hope.—TJie 'Sadd' of the Upper Nile. very interesting book of travel, 'The Heart of Africa,' a translation of which into English was published in 1873, we find full information about ' Ambatch,' which will now be quoted or abridged;— ' What, however, most interested me was the unlimited variety in the kinds of water plants which abounded in the floods, the sport of the winds and waves. Among them the Herminiera, known under the native name ambatch, has already been the subject of general remark ; it plays so prominent a part in the waters of the Upper Nile that it might fairly be designated the most remarkable of the aquatic plants. ' My predecessor, Kotschy, who did not know that it had already been observed by Adanson in Senegambia, named it Aedemone mirabilis, which was corrupted into the still more wonderful name of Anemone mirabilis, and so appeared in many books which treated of Africa. The ambatch is distinguished by the almost unexampled lightness of its wood, if the fungus-like substance of the stem deserves such a name at all. It shoots up to fifteen or twenty feet in height, and at its base generally attains a thickness of about six inches. The weight of this fungus-wood is so insignificant that it really suggests comparison to a feather. Only by taking it into his hands could any one believe that it were possible for one man to lift on his shoulders a raft made large enough to carry eight people on the water. The plant shoots up with great rapidity by the quiet places of the shore, and since it roots merely in the water whole bushes are easily broken off by the force of the wind or stream, and settle themselves in other places. . . . This is the true origin of the grass-barriers so frequently mentioned as blocking up the waters of the Upper Nile, and in many places making navigation utterly im- practicable. Other plants have a share in the formation of these floating islands which daily emerge like the Delos of tradition; among them in particular the Vossia grass, and the famous papyrus of antiquity, which is at present nowhere to be found either in Nubia or in Egypt.'

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 503 ' As we progressed farther the river islands became more and more narrowed by the surrounding masses of impenetrable grass. The ambatch is here almost excluded by the Vossia grass, but only to appear at the mouth of the waters. . . . Here we came across numbers of Shillooks fishing" in their light canoes of ambatch, darting through the water almost as quickly as the fish themselves.... So light are these canoes that one man can carry three of them on his shoulders, although each canoe is capable of holding three men. From a dozen shoots of ambatch of about three years' growth a canoe of this kind can easily be produced ; at about six feet high the stem goes off rapidly to a point, so that a bundle of them needs only to be tied together at the extremities, and there is at once obtained a curve that would grace a gondola.' Here then is a direct conflict of testimony. On the one hand Dr. Schweinfurth, a great traveller and explorer as well as an eminent botanist, states from personal observation that the ' Ambatch,1 Herminiera elaphroxylon, is the true origin of the ' grass-barrier' which blocks up the Upper Nile ; and, on the other hand, we have Sir William Garstin, an eminent engineer, holding a high post under the Egyptian Govern- ment, who spent months on the Upper Nile, and watched the operations carried on for the removal of the ' grass-barriers' (the ' Sadd'), stating that the main constituents of the ' Sadd ' are the Papyrus and the ' um-soof' ( Vossia procerd) reeds, and that the ' Ambatch ' has been unjustly accused of assisting in forming the barrier. Possibly Dr. Schweinfurth's observations were not made just where Sir William Garstin investigated the composition of the barrier. And Dr. Schweinfurth says that in places the 'Ambatch' was almost excluded by the ' um-soof.' Also it is quite conceivable that in some places as good a block may be made by Papyrus and Vossia alone as by all three plants combined in other places. And the objection that the stem of the' Ambatch' is too light and brittle to withstand great pressure does not seem to have been verified by experiment and may not be fatal. The lightness and brittleness are admitted ; but would it be possible for

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 504 Hope.—The 'Sadd' of the Upper Nile. 3. plant to have a stem generally six inches thick at the base, and to shoot up to fifteen or sixteen feet in height, unless the stem had a certain degree of strength ? And doubtless the ' Ambatch ' attains its height above the water by the support which the Papyrus and Vossia afford it. It must therefore be flexible enough not to mind pressure. ' ; But Dr. Schweinfurth is not the only observer and botanical authority who may be quoted against Sir William Garstin on the side of the ' Ambatch.' In ' Plantae Tinneanae,1 by Theodori Kotschy and Joannis Peyritsch, ' Ambatch ' is not botanically figured, that having been done before by Heuglin; but a lithographed frontispiece shows a landscape with ' Am- batch ' and papyrus and other plants growing together in the foreground. The ' Ambatch' is growing much higher than the papyrus, and the stems are bent down or broken off at various heights. The stems are therefore brittle ; but one can easily imagine that they form a substantial woof in the. entanglement of which the papyrus and 'um-soof form the warp. And the branches and twigs of the plants, being thickly set with stout prickles like those of a rose plant, would add to the trouble. In the 'Proemium' M. Kotschy tells us that, according to Lejean,' les deux rives sont couvertes de Papyrus, mais sur- tout de l'arbre aquatique appele Ambadj, qui, pendant l'^poque de la fleuraison, c'est-a-dire en feVrier et mars, releve encore la beaute de son feuillage vert et e'toile' par des fleurs d'un jaune brillant.' The Tiring botanists say that it is in the neighbourhood of Mt. Dinka (Njemati) one first sees thickets (or bushes) of Am- badj (Herminiera elaphroxylon) which become more and more frequent as one travels towards the south, and are associated with Pistia stratiotes, and Nymphea round about them ; and, near Hille-Kaka, a fern equally floating, Ceratopteris thalictroides, comes in their company. At the mouth of the River Sobat much of the surface of the water is covered by reeds, and there, round the reeds and other plants above mentioned, one meets with Asolla nilotica growing very large, which is

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The ' Sadd' of (he Upper Nile. 505 figured on Plate 27 of the work. Further on the botanists 'say:— ' L'Herminiera, qui porte le nom d'Ambadj, pousse pendant 5 ans de ses grosses racines principales, qui sont horizontales, place"es constamment sous la surface de l'eau, et garnies de radicelles capillaires tres-nombreuses, ses troncs coniques qui atteignent souvent une hauteur de 20 a 25 pieds: pendant les cinq annexes suivantes, ces troncs de"pe"rissent, et une nouvelle pe'riode de vegetation commence a se produire.' In the dry season, fires in the neighbouring jungle frequently reach the ' Ambatch,' and thus seriously endanger the boats of the inhabitants. Herminiera elaphroxylon was first described by Guillemin, Perrotet, and Richard, in their Flora of Senegambia, and was therein figured: and it again appeared in Speke's book, 'The Source of the Nile,1 in the botanical Appendix by Thomson. In Kotschy and Peyritch's book the authors remark as follows:— ' In stagnantibus aquis ad ripas Nili et Bahr-Ghasal planta haec mirabilis radicibus intertextis cum quibusdam aliis plantis insulas format, quae ventis hue atque illuc agitantur. ' Crescit in fossis Nili albi inter Schilluk insulas necnon in Bahr-Ghasal copiaque navigantibus impedimentoest. Arabice Ambadj dicitur.' Of Pistia siratiotes MM. Kotschy and Peyritch say that it is very abundant in the Bahr-Ghazal,' ou il constitue des iles flottantes, en socie'te' des Cyperus colymbates, des Hermi-. niera elaphroxylon, des Nymphaea, et divers autres plantes.' Besides Cyperus colymbates of Kotschy and Peyritch, Mr. Clarke shows another floating Cyperus of the Nile, namely, C. nudicaulis of Poiret, collected on the White and Gazelle Niles by Schweinfurth. These are small plants, with long, pendent roots ; but in quantity they must play a considerable part in the formation of ' Sadd.' On referring to the Botanical Appendix to Speke's work, ' The Source of the Nile,' we find in its place in the order Leguminosae, Herminiera elaphroxylon, Guill. and Per.,

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 506 Hope.—Tlie ' Sadd' of the Upper Nile. the 'ambash' or pith tree of the Nile from 30 to 8° N. lat. There can therefore be no doubt as to the identity of ambatch, or ambadj, or ambash, with Herminiera elaphroxylon. And, when we find Schweinfurth's account of the habits and propensities of ' Ambatch' thus corroborated by the evidence of Kotschy and Peyritch, we cannot but find it guilty of being a chief constituent of' Sadd.'

Smaller Plants of the ' Sadd.' Those mentioned in Sir William Garstin's report are— Pistia stratiotes, Ulricularia, Azolla, and Ottellia. These are said to grow mingled with the larger plants we have discussed, but not to play an important part in forming the blocks in the Bahr-al-Jebel; while, on the contrary, on the Bahr-al-Ghazal the ' Sadd' is composed chiefly of them. They are, there, bred in Lake Ambadi and other shallow lakes adjoining the river into which they are swept by floods. Pistia stratiotes has already been mentioned as floating down the Nile far above the ' Sadd ' region, from the Victoria Nyanza (Lake), probably, and again .as being a plant of the ' Sadd' region of the Mountain Nile: it was absent in 1900, but in 1901, when the river was open, there was a continuous stream of it floating down. ' It is a very common tropical water-weed, out of which many species and even separate genera have been made. It is referred to the same order as duckweed . . . but is very different in appearance, and very much larger. . . . Like duckweed, it propagates itself with great rapidity, and frequently completely covers tropical ponds and water-tanks with a coating of verdure, keeping the water underneath fresh and cool. It floats on the water and sends down a quantity of long feathery roots, which very rarely reach the bottom. The plant consists of a rose-shaped tuft of wedge-shaped leaves, two to five inches long. . . . Each plant sends out several runners, and upon the ends of these other similar plants are formed, which again send out runners, until in a short time the surface of the water is covered.' It was figured in the Botanical Magazine, No. 4564.

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 507 Utricularia is a genus, containing several floating species, the roots, stems, and leaves of which are furnished with numerous membranaceous vesicles or small bladders, which during the early stage of the plant are filled with water, but when the flowers are ready to expand become filled with air. The British species, at least—called Bladderwort—are thus floated upwards, but only sufficiently to let the flowers rise above water, the rest of the plant remaining submerged. 'After the season of blossoming the vesicles become again filled with water, and the plant descends to ripen its seed at the bottom,' where, on the Nile, it probably fraternizes with the roots and stems of the other' Sadd ' plants. Another group of Utricularia consists of species which grow at higher altitudes, and have quite a different habit from that just described. Azolla is a very curious genus, belonging to the fern allies. The species found in the Upper Nile is A. nibtica. The few species all float upon water, forming green or reddish patches, frequently several yards across, and they have creeping rhizomes which throw down roots towards the bottom of the pool or stream. ' The species occur from Australia and New Zealand as far as New York. One has been found in Western Africa by Vogel.' A. filiculoides; found in California, often grows in densely crowded masses, the plants being usually much larger than those of the Eastern species. A. nilotica was got on the Shir6 River, in East Central Africa, by Dr. (now Sir John) Kirk, who noted it as ' small, creeping' (on the surface of the water),' and sending down roots all along,' and also by him on the Luabo River, ' floating, with Pistia and Trapa.' Ottellia, another genus of' Sadd' plants named by Sir William Garstin, consists of 'perennial herbs inhabiting the mouths of the Nile, Ganges, and Australian rivers, and eaten as potherbs in India. They are quite stemless.' The size as well as the shape of the leaves varies much. The Indian plant is O. alismoides, Persoon. One other minor ' Sadd' plant is mentioned by Sir William Garstin, namely Aldrovanda. This is a genus of Droseraceae

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 '508 Hope.—The 'Sadd' of the Upper Nile. (Sundews) containing, says Lindley, only a single species, A. vesiculosa, found in Southern Europe, and growing in still waters. The leaves are pellucid, and are widened at the extremity into two lobes which in Europe are generally found closed. In 1873 Stein discovered that the bilobed leaves open under a sufficiently high-temperature, and when touched suddenly close and thus entrap aquatic animals. The leaves sometimes contain bubbles of air, and were formerly supposed, to be bladders : hence the specific name of vesiculosa. Aldro- vanda is destitute of roots and floats freely in the water. (' Insectivorous Plants,' Darwin, 1871, p. 321.) The leaf-stalk is flat, not inflated. Mr. Clarke says the plant is only rarely met with in the ' Sundribans' of Bengal, but he cites it as an instance of a genus occurring on both the Nile and Ganges.. Ceratopteris thalictraides, Brongn., mentioned by Kotschy and Peyritch as being one of the floating components of the ' Sadd ' in the Gazelle Nile, is a fern, but very anomalous in. its structure, placed by Hooker and Baker in the tribe, or family, Pterideae, but considered by other botanists as so- paradoxical that it ought to be placed in a tribe, or even a sub-order, by itself. It is the only species of its genus, but it was originally named by Linnaeus Acrostichum thaliclraides. It has since been characterized by later authors under no less than nine different genera, and a dozen specific names. The fern grows in separate plants. The stipes or stalks of the fronds are thick, inflated, filled with large air-cells. The fronds are of two sorts, one barren and floating, the other longer, erect and fertile, and succulent in texture. The plant is found widely spread in the tropics of both hemispheres, growing, said Mr. John Smith, in wet places or even in shallow water, the sterile fronds viviparous ; and the ready germination of the spores, and rapid growth of the fronds, make it abundant in its habitats. Mr. Smith says this is one of the few ferns that are annual. Colonel Beddome, the authority on Indian ferns, says it grows throughout India, Ceylon, and the Malayan Peninsula up to 3,000 feet elevation, and is common in tanks (ponds), ditches, and swampy places, or even on dry ground

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 509 in the rains.' And he does not think it is an annual, at least in cultivation, if kept very moist or in water, as he kept the same plant growing for some years at Ootacamund in the Nilgiri Mountains, 7,000 feet or so above the sea. Mr. C. B. Clarke, who, in the Transactions of the Linnaean Society published a ' Review of the Ferns of Northern India,' notes regarding this fern :—' In rice-swamps, floating ; but much more commonly erect, tufted, in ditches, or even in dry spots during the rains. The floating and erect forms both produce their barren and floating fronds. In ditches the rhizome is somewhat creeping and stout' T. Moore wrote :—' Either floating or attached to the soil in shallow, still, or slightly moving waters.' The plants in the Bahr-al-Ghazal must be quite off the ground. The present writer found the plant growing gregariously in the Dehra Dun, North-Western India, in briskly running shallow water, and there it was well-rooted in the ground, and liable to be submerged with the rise of the water. In Florida, U. S. A., it is recorded as floating. The late Rev. C. S. Parish found C. thalictroides growing in his garden in Maulmain, Burma, on gravel walks during the rainy season; and the late Mr. H. C. Levinge, a very distinguished amateur collector of Indian ferns, gathered it ' on an old wall at Siliguri in the Darjiling Terai.'

VEGETATION IN THE SWAMPS OF LOWER BENGAL. When consulted as to the plants which form the Nile ' Sadd,' Mr. Clarke was led to think back to his life long ago, in Lower Bengal and Assam, when in the course of duty he had to travel about in a boat through the great swamp which extends over the zillas (counties) of Sylhet, Comilla, and Maimensingh. These water plants of many sorts unite to form not only barriers in streams, but, during the annual floods of the Ganges, Brahmaputra, and Surma Rivers, a dense mass of floating vegetation, extending perhaps 100 miles from east to west, and as much from north to south; and Mr. Clarke very kindly furnished some notes in which he contrasted the conditions prevailing in Bengal with those on

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 5io. Hope.—The 'Sadd' o/.t/u Upper Nile.- the Nile, and showed how similar the vegetation is in the two . localities. During the floods, Mr. Clarke says, the only- means of communication is by water; and away from the main streams the inhabitants can get about nowhere except from point to point where the villages are built on isolated, artificially-raised, mounds, or on river banks. This they do along straight lanes through the floating vegetation, which are kept open by the boat traffic. Mr. Clarke points out that the main difference between the Bengal floating vegetation and the Nile ' Sadd ' is that the first-named grows in water which is practically at rest (it really moves in mass, though extremely slowly, from north-west to south-east), but the floating vegetation if forced into the main rivers is lost owing to their vast width ; whereas the' Sadd ' plants of the Nile, though reared in the still waters of the lakes and lagoons, are broken off into clumps and carried into the river by the strong winds which accompany the annual rise of the river, and there become potent for mischief. The interesting point to Mr. Clarke is the remarkable way in which some of the African ' Sadd ' plants are represented in Bengal by closely allied ' representative' species. The two 'Sadd' floating species of Cyperus (C. colymbates, Kotsc. and Peyr., and C. nudicaulis, Poir.), have in Bengal two representatives, C. cepJialotes, Vahl., and C. platystylis, R.Br., the seeds of which float and germinate in the water. The seeds of C papyrus, and some other species which at all events begin their life rooted in the ground, are heavy and sink to the bottom, there to germinate in the mud. The representative of' Ambatch' (Hirminiera elaphroxylon, Guill. and Perrot) in Bengal Mr. Clarke finds in Aeschynmnene aspera, Linn., also a leguminous plant, of a genus which stands next to Herminura in Bentham and Hooker's ' Genera Plant- arum.' Herminiera is, he says, only Aeschynomene writ large. The wood, or ' pith,' of this shrub is the well-known ' Sola' of Bengal, which is used for making sun-hats, swimming-jackets, and covers under which to keep iced drinks cool, and for many other purposes where elasticity and lightness are

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 511 required, such as for floats for fishing nets. To construct some of these articles the soft corky stem is cut into thin slices and pasted together. It is sold in the bazars of Calcutta, being brought from the neighbouring marshy places, where it grows to a great size. Aeschynomene aspera (' Sola') itself seems to be a Nile plant, for in the Botanical Appendix to Speke's book is an entry—Aeschynomene indica, L.,' Solah ' of India, in marshes generally 50 S. to 20 N. lat. But this range is all south of the ' Sadd ' region. In September, it is said (the height of the dry season), at 30 S. lat., this plant lies dead on the dry mud; it grows erect 7 feet high, and is used for floats for nets. Ae. Schimperi, Hochst, is another equatorial African plant, and is said to be a species of Indian Solah (pith), a bushy tree, growing 20 feet high. Azolla nilotica is represented in Bengal by A.pinnata,R. Br., and the Nile Ottellia by O. alismoides.'Pers.—if indeed the plants are specifically different. Plants which are identical on the Nile and in the Bengal swampsare Vosstaprocera, Trapanatans,lAnn.,Pistia stratiotes, L., Aldrovanda vesicularis (very rare, though perhaps plenti- ful in places), Nymphaea Lotus and TV. stellaris, and Cerato- pteris thalictroides. Mr. Clarke is inclined to consider Pistia stratiotes as the chief constituent of the rotting vegetation in the Bengal swamps andjheels, which in the middle of the rains forms a floating mass from 6 to 24 inches thick, on which birds run and which will often carry a man. And he says that most of the plants which float, or grow on floating masses of Pistia, other weeds and earth mixed, can also grow on mud; while the whole of the rice-field weeds may grow on such floating masses. Even seedlings of trees, as olBombax and Erythrina, sometimes appear plentifully on the floating mass. It is by notes such as these which Schweinfurth, Kotschy and Peyritch, Mr. Clarke, and other botanists who have been great travellers, give us of the habits and habitats of plants, that the dry bones of systematic botany are made to live and be interesting to the general reader.

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'SADD' IN AMERICA. In conclusion, a comparison may be added with the American ' Sadds,' which have an entirely different composition. Mr. T. A. Sprague, of the Herbarium in the Royal Gardens, Kew, who has travelled across South America by way of the Amazon Valley, says that neither on the Amazon nor on the Orinoco do masses of floating plants occur in sufficient bulk to hinder navigation. This was not to be expected in such wide and deep rivers. But Mr. Sprague pointed out that something of the sort occurs in Guiana, and referred the writer to the very interesting book, ' In the Guiana Forest,' by Mr. James Rodway, F.L.S. (T. Fisher Unwin, London, 1895), from which it appears that serious, though temporary, obstructions to the flow of the great rivers in that region (the Essequibo, &c.) are caused chiefly by two plants, Montrichardia arboresceiis and Panicum ehphantipes. At p. 107 of his book Mr. Rodway says : ' The tall trees cannot hold their own in the mud ; therefore they give place to a different type which has little or no trunk, and sits down as it were to anchor itself by means of special contrivances. Several species of Leguminosae, in- cluding Drepanocarpus lunatus, Muellera moniliformis, and Hecastophyllum Brozvnii, form dense thickets and extend as far from the bank as they dare. In front of these is an advance guard of mocca-mocca [Montrichardia arborescens), which is as it were drawn up in rank to keep back the flood. Growing in the water, this monster arum develops great club-like stems, which come up as close to each other as they can pack, and rise like rows of palisades to the height of twelve feet or more above the surface. A3 if this were not a sufficient encroach- ment on the open space, the floating island grass {Panicum elephantipes) anchors itself to the mocca-mocca or bushes, and extends just as far across as the rapid current will allow. In dry weather, when the water is low and the stream has little power, the extensions from either side meet in the centre, and close the passage-way for a time—only, however, to be torn away in great masses as the floods come. At such times great patches, fifty feet or more in diameter, are seen floating down

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 513 stream, sometimes carrying with them monster camoudies {Boa murind) or other snakes.' Mr. Clarke caps this by telling how a rhinoceros was carried down a Bengal river to near Chittagong, and there caught and sent to the London Zoo- logical Gardens, where it was described as a new species by Mr. Sclater (R. lasiotis). ' As these masses are caught by the sea-waves they are thrown back upon the beach, where they lie in great heaps until, dying, they go to help make up that extension of the coast-line which is continually driving back the waves to a greater distance. Sometimes a great tree, whose timber is light enough to float, gets entangled in the grass and becomes the nucleus of an immense raft, which is continually increasing in size as it gathers up everything that comes floating down the river. The grass extends over the whole mass and mats it together until a formidable obstacle is produced ; but, notwithstanding all its efforts, the dam is imperfect When eight or ten inches of rain fall in a day, and the river rises sixteen to twenty feet, the barrier must go. However (much) it may be attached to the bottom by a thousand anchors, it has to give way when the rise takes place, and here the hollow stems help in its destruction. By their great numbers they act as buoys, drag the great tangle of trees and bushes to the surface, unloose their own anchorage, until the mass sails away, ever on and on, to be broken in pieces and dashed on the shore, or perhaps carried far out to sea.' It sometimes happens that a very obstinate obstruction succeeds in withstanding the flood, which by and by comes and deposits fresh masses of similar material on the fast- forming bank until it becomes an impenetrable barricade, narrowing the channel to a considerable extent. ' The waters become higher, and the current swifter. Something has to go, but it is not this late erection. The opposite bank is under- mined, one bush after another goes down with the flood, trees fall over and are also carried away, and a few months later the great river has a new bend.' And sometimes such an obstruction is formed in the middle of the stream, in a shallow place.

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 5H Hope.—The 'Sadd' of the Upper Nile. Then a little island is gradually formed, and mocca-mocca roots get stranded and begin to grow, and in a year or two a dense living palisade of Montrichardia protects the small island from being washed away. ' The little island lengthens down stream to a considerable distance. The semicircle of gigantic arums is sufficiently elastic to bend before the weight of water ; the plants may be torn off by the roots, but never broken off.1 ' The great rivers of Guiana all contain islands of different sizes, some as many as ten miles long, and it may be con- fidently stated that nearly all have been built up in this way, by means of the mocca-mocca, with the assistance of the host of thorny Papilionaceae.' From Mr. Rodway's description it appears that the obstructions caused on the Guiana rivers are caused or intensified by the mocca-mocca being stranded in the water, or growing up in it from roots which have sunk to the bottom, and by the interlacing of floating grass with its thickly planted stems, and the ' host of thorny Papilionaceae.' On the other hand, the ' Sadd ' of the Upper Nile consists mainly of plants which grow in the lateral lakes and lagoons, or on the banks of the main channel, and are forced in masses into the river by floods and winds and swept down by the current until they unite and find a point on the bank or in a narrow part of the channel which brings them to a stand, when they form a floating block under which further-supplies of material coming from up-stream are sucked in and go to increase the vertical thickness of the mass both above and below water. The consequence of a block of ' Sadd ' on the Nile is increased flooding of the land on either side of the river, and disastrous loss of water in the lakes and lagoons, and by evaporation, for it does not appear that there is any such solid ground, within reach of the current, into which the river can eat and form a new channel, as there is in the case of the Guiana rivers ; and the floating power of the hollow-stemmed and buoyant mocca-mocca prevents the blocks formed by it and the floating grass from being any- thing like so permanent as those on the Nile.

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of the Upper Nile. 515 Another case of obstruction by aquatic vegetation in America is found in Florida, U. S., North America, where— originally introduced from tropical South America for its beauty as a flowering plant—the so-called Water Hyacinth has become' naturalized, and has increased to such an enormous extent in the St. John's River as to cause serious apprehen- sion that-navigation may be altogether closed. A Report to the U. S. Department of Agriculture, Division of Botany, by Mr. H. J. Webber, published as Bulletin No. 18 of the De- partment (Washington, 1897), gives full information con- cerning the vegetation which causes the obstruction, and the nature of the damage, of various sorts, caused by it. The . Water Hyacinth, Eichhornia speciosa, Kunth (syn. E. crassipes (Mart.), So\ms='Piaropns crassipes (Mart.), Britton), is the main factor in the block. It belongs to the Pontaderiacea Order. The leaves form a rosette one to two feet high, which remains above water as the plant floats; the basal portions of the leaf-stalks of young plants are strongly swollen, but as the plant becomes older the swellings gradually disappear, and the petiole lengthens. The swellings on the petioles of the young leaves act as air-reservoirs, and thus ensure the stability of the young in water. Old plants become thoroughly entangled, and are in no danger of being overturned. The long petioles are full of air. The roots form a dense, bushy mass, reaching in many cases a length of over two feet. The plant bears spikes of light-blue or violet flowers, and blooms freely, and this has led to its being widely cultivated in America and Europe. Plants, now coming into flower (July 1902), may be seen in the tank in the Victoria Regia house in the Royal Gardens, Kew. The water hyacinth is mostly limited in its growth to sluggish fresh-water streams, bayous, lakes, ponds, &c. In Florida the plants are generally found lining the shores of lakes and rivers in immense numbers. In certain lakes the entire shores are lined with a solid mass for fifty to several hundred feet wide, and small tributary creeks of the St. John's River are entirely covered. The main channel of the river N n

Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 516 Hope.—Tlie 'Sadd' of the Upper Nile. remains clear unless masses of the plants become so packed together as to produce a block. In most places the hyacinth grows to some extent on the muddy shores of the rivers and lakes, and the stolons become so entangled that the plants whose roots penetrate the soil serve to moor large floating masses to the shore. Masses get loose and are blown by the wind, even 25 miles, up stream, and there form solid masses. Other large masses are carried by the current down to the ' sea. Mr. Clarke says that the American Eichfwrnia is represented in the Bengal swamps by the allied genus Monochoria, which has the same habit and mode of growth. Mr. Webber describes the method of self-propagation of the plant, and notices its introduction into Florida and its present distribution in the State. He gives a graphic account of the damage caused by obstruction to the rafts in which timber is brought down the river, and to fishing with nets, and an illustration in his Report, from a photograph, shows at once the great width of the St. John and the extent to which it is in places covered by Eichhomia, with large river steamers imbedded in it Masses of the plant floating down stream get banked up against the long low bridge which carries a railway across the river, or estuary, and act as a dam to the water. Another illustration shows how the weed, floating down stream, is diverted by booms into docks similarly con- structed, whence it is taken on shore and used as manure. Observations arc recorded as to the effect on health of so much, vegetation collected together in the water, and along the river banks; but it may be doubted whether the weed does any harm while floating and growing. In its manner of growing and spreading over the surface of sluggish water in a continuous sheet the EichJwniia strikingly resembles Pistia stratiotes, which plays no mean part in the ' Sadd' of the Upper Nile, and is so striking a feature in the great swamps of Bengal; but there does not seem to be any tall-growing plant in Florida at all corresponding to the Papyrus, Um-soof, and Ambatch of the Nile,.or to the mocca-mocca of the Essequibo.

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