506 Hope . — The ‘ Sadd ’ of the Upper Nile . 
the ‘ ambash ’ or pith tree of the Nile from 3 0 to 8° N. lat. 
There can therefore be no doubt as to the identity of am- 
batch, or ambadj, or ambash, with Herminiera elaphroxylon. 
And, when we find Schweinfurth’s account of the habits and 
propensities of ‘ Ambatch ’ thus corroborated by the evidence 
of Kotschy and Peyritch, we cannot but find it guilty of being 
a chief constituent of ‘ Sadd.’ 
Smaller Plants of the e Sadd/ 
Those mentioned in Sir William Garstin’s report are— 
Pistia stratiotes , Utricularia , Azolla , and Ottellia. These 
are said to grow mingled with the larger plants we have 
discussed, but not to play an important part in forming the 
blocks in the Bahr-al-Jebel ; while, on the contrary, on 
the Bahr-al-Ghazal the ‘ Sadd ’ is composed chiefly of them. 
They are, there, bred in Lake Ambadi and other shallow 
lakes adjoining the river into which they are swept by floods. 
Pistia stratiotes has already been mentioned as floating 
down the Nile far above the c Sadd 5 region, from the Victoria 
Nyanza (Lake), probably, and again as being a plant of the 
‘ Sadd ’ region of the Mountain Nile : it was absent in 1900, 
but in 1901, when the river was open, there was a continuous 
stream of it floating down. ‘ It is a very common tropical 
water-weed, out of which many species and even separate 
genera have been made. It is referred to the same order as 
duckweed . . . but is very different in appearance, and very 
much larger. . . . Like duckweed, it propagates itself with great 
rapidity, and frequently completely covers tropical ponds and 
water-tanks with a coating of verdure, keeping the water 
underneath fresh and cool. It floats on the water and sends 
down a quantity of long feathery roots, which very rarely 
reach the bottom. The plant consists of a rose-shaped tuft of 
wedge-shaped leaves, two to five inches long. . . . Each plant 
sends out several runners, and upon the ends of these other 
similar plants are formed, which again send out runners, until 
in a short time the surface of the water is covered.’ It was 
figured in the Botanical Magazine, No. 4564. 
