Reconquest of the Water 
interrupted only by occasional knolls of granite or other 
tock. 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.? 
The two plants which seem to feplace Phragmites in 
the Nile valley are the papyrus, a giant sedge with 
stems often 1o 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 (ie. 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 (1870-1873) 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.” 
The method adopted by Major Matthews in rgo1— 
134 
