In another place he describes acacia groves on the right bank of the White Nile above Khartum, with their enormous white bulbous thorns,[87] and their oozy lumps of amber-coloured gum. He notes the remarkable fact that little, if any, of the floating vegetation of the Upper Nile reaches Egypt. He describes the jungles of papyrus, “fifteen feet high,” the floating grass barriers and the sudd (which he calls _sett_); the _suf_ reeds, the water-ferns, the floating _Pistia stratiotes_ (like a pale-green lettuce), the duck-weeds, the beautiful white and blue waterlilies. When he reached the vicinity of the water-parting between the Nile and the Congo, he had entered the forest region of West-Central Africa. This mighty tropical forest has no great reverence for geographical boundaries, but overlaps in several places the watershed of the Nile, while of course it exists in patches in the basins of the Shari, the Benue, the Niger, and on the coast belt of Upper and Lower Guinea. Perhaps the most marked feature of it, the clearest indication of its West African nature, is the existence of the climbing _Calamus_ palm, which is never found in typical East Africa. The wonderful “gallery”[88] forests are described as follows:-- “Trees with immense stems, and of a height surpassing all that we had elsewhere seen (not even excepting the palms of Egypt), here stood in masses which seemed unbounded, except where at intervals some less towering forms rose gradually higher and higher beneath their shade. In the innermost recesses of these woods one would come upon an avenue like the colonnade of an Egyptian temple, veiled in the leafy shade of a triple roof above. Seen from without, they had all the appearance of impenetrable forests, but, traversed within, they opened into aisles and corridors which were musical with many a murmuring fount. Hardly anywhere was the height of these less than seventy feet, and on an average it was much nearer one hundred; yet, viewed from without, they very often failed to present anything of that imposing sight which was always so captivating when taken from the brinks of the brooks within. In some places the sinking of the ground along which the gallery-tunnels ran would be so great that not half the wood revealed itself at all to the contiguous steppes, while in that wood (out of sight as it was) many a ‘gallery’ might still exist.”