Read it through once

Lower Egypt is the gift of the Nile, but it is not so much the Nile as these neglected water plants which made the rich lucerne, cotton, and food crops of Lower Egypt possible. Amongst the Egyptian Reeds one especially is of great importance. The _Papyrus antiquorum_, ten feet high, has much the same habit as our Phragmites and other water plants. It forms dense, almost impassable thickets, sometimes completely occupying and choking a small valley, or leaving only a passage, often changing and half choked, through a larger one. This, with other plants, makes the "sudd" of the Nile, which is one enormous accumulation of marsh plants and reeds floating on the water and covering a length of over 500 miles.