The hindrances to our progress caused by the excessive vegetation began now to give us some anxiety. All day long we were bewildered not only by the multiplicity of channels, but by masses of grass, papyrus, and ambatch, which covered the whole stream like a carpet, and even when they opened gave merely the semblance of being passages. It is quite possible that the diversion of its course to the east, which, for sixty miles the Nile here takes, may check the progress of the stream, and be in a measure the cause of such a strange accumulation of water-plants. Certain it seems that neither any exceptional depth of water, such as may occur in particular years, nor yet any general overflow wider than usual, avails to exercise the slightest influence upon this exuberant vegetation. Were it a coating of ice it would split itself into fragments under the pressure of the stream, but here is a real web of tough tangle, which blockades the entire surface. Every here and there, indeed, the force of the water may open a kind of rift, but not corresponding at all with the deeper and true channel of the stream. Such a rift is not available for any passage of the boats. The strain of the tension, which goes on without intermission, has such an effect in altering the position of the weedy mass, that even the most experienced pilot is at a loss how to steer, consequently every voyage in winter is along a new course, and through a fresh labyrinth of tangle. But in July, when the floods are at their highest, navigation can be carried on along well nigh all the channels, since the currents are not so strong, and the vessels are able to proceed without detention to their destinations. [Sidenote: GRASS TANGLE.] Thick masses of little weeds float about the surface of the water, and by forming a soft pulp, contribute an effectual aid to bind together the masses of vegetation. Like a cement this conglomerate of weeds fills up all the clefts and chasms between the grass and ambatch islands, which are formed in the back-water where the position is sheltered from the winds and free from the influence of the current. There are two plants, at a superficial glance hardly distinguishable, which perform the largest share in the formation of this compact web. One of them is the thin-membraned water-fern, the _Azolla_; the other (which is quite familiar to every visitor to the tank of the _Victoria regia_) being the _Pistia_, which can hardly fail to recall a head of lettuce. The sailors of the White Nile call it the “negro tobacco,” probably with reference to the dwarfed growth of the two kinds of tobacco in the negro lands. Besides these, our duck-weeds (_Lemna_) and Tussieua of various sorts intertwine themselves with the mass, and the different African representations of our commonest water-plants play a part by no means unimportant.