508 Hope . — The * Sadd ’ of the Upper Nile . 
(Sundews) containing, says Lindley, only a single species, 
A. vesiculosa , found in Southern Europe, and growing in still 
waters. The leaves are pellucid, and are widened at the 
extremity into two lobes which in Europe are generally found 
closed. In 1873 Stein discovered that the bilobed leaves 
open under a sufficiently high temperature, and when touched 
suddenly close and thus entrap aquatic animals. The leaves 
sometimes contain bubbles of air, and were formerly supposed 
to be bladders : hence the specific name of vesiculosa. Aldro- 
vanda is destitute of roots and floats freely in the water. 
(‘ Insectivorous Plants/ Darwin, 1871, p. 321.) The leaf-stalk 
is flat, not inflated. Mr. Clarke says the plant is only rarely 
met with in the ‘ Sundribans ’ of Bengal, but he cites it as 
an instance of a genus occurring on both the Nile and Ganges. 
Ceratopteris thalictroides , Brongn., mentioned by Kotschy 
and Peyritch as being one of the floating components of the 
■ Sadd ’ in the Gazelle Nile, is a fern, but very anomalous in 
its structure, placed by* Hooker and Baker in the tribe, or 
family, Pterideae , but considered by other botanists as so 
paradoxical that it ought to be placed in a tribe, or even 
a sub-order, by itself. It is the only species of its genus, but 
it was originally named by Linnaeus Acrostichum thalictroides. 
It has since been characterized by later authors under no less 
than nine different genera, and a dozen specific names. The 
fern grows in separate plants. The stipes or stalks of the 
fronds are thick, inflated, filled with large air-cells. The 
fronds are of two sorts, one barren and floating, the other 
longer, erect and fertile, and succulent in texture. The plant 
is found widely spread in the tropics of both hemispheres, 
growing, said Mr. John Smith, in wet places or even in shallow 
water, the sterile fronds viviparous ; and the ready germination 
of the spores, and rapid growth of the fronds, make it abundant 
in its habitats. Mr. Smith says this is one of the few ferns 
that are annual. Colonel Beddome, the authority on Indian 
ferns, says it grows throughout India, Ceylon, and the Malayan 
Peninsula up to 3,000 feet elevation, and is common in tanks 
(ponds), ditches, and swampy places, or even on dry ground 
