Reconquest of the Water 



interrupted only by occasional knolls of granite or other 

 rock. The valley varies from five to fifteen miles in 

 width, and about five hundred miles of flat marshy 

 land has to be traversed. In the rainy season this is 

 all flooded, and even at the driest time of the year the 

 vegetation is rank and exuberant. 9 



The two plants which seem to replace Phragmites in 

 the Nile valley are the papyrus, a giant sedge with 

 stems often 10 feet high ending in a tassel of dark 

 green leaflets, and a grass, Vossia procera, said to be 

 sometimes 20 feet long. But these have submerged 

 tough and thick rhizomes (i.e. horizontal stems half 

 submerged). When the country is flooded, as during 

 the annual floods of the Sobat river, "floating islands," 

 quite similar to the small patches of Phragmites but on 

 a gigantic scale, are produced through masses of these 

 rhizomes being detached from the mud and broken off. 

 Such floating masses get into the main current, and at 

 any sharp bend or curve are apt to become caught and 

 accumulate so as to form a barrier stretching right across 

 the river. Everything floating becomes heaped up above 

 this barrier. Of such floating plants there are enormous 

 quantities (such as Pistia stratiotes, Azolla, Aldrovanda); 

 new masses of grass are for ever arriving. Some are 

 sucked under the barrier, others pile up against it until 

 the whole channel is thoroughly blocked by a mass of 

 vegetable matter 4 or 5 feet or more in thickness, 

 and extending for miles. These sudd-blocks seem to be 

 irregular in their appearance. The army of the Emperor 

 Nero turned back in consequence of one of them. Sir 

 Samuel Baker found but little sudd in his first expedition, 

 but in his second (1 870-1 873) he had serious difficulties 

 in cutting a channel through it. Major Peake had to cut 

 his way through twenty-five miles of sudd in one place. 10 



The method adopted by Major Matthews in 1901- 



*34 



