Hope . — The ‘ SadcT of the Upper Nile. 507 
Utricularia is a genus, containing several floating species, 
the roots, stems, and leaves of which are furnished with 
numerous membranaceous vesicles or small bladders, which 
during the early stage of the plant are filled with water, but 
when the flowers are ready to expand become filled with air. 
The British species, at least- — called Bladderwort — are thus 
floated upwards, but only sufficiently to let the flowers rise 
above water, the rest of the plant remaining submerged. 
‘After the season of blossoming the vesicles become again 
filled with water, and the plant descends to ripen its seed at 
the bottom/ where, on the Nile, it probably fraternizes with the 
roots and stems of the other ‘ Sadd 5 plants. Another group of 
Utricularia consists of species which grow at higher altitudes, 
and have quite a different habit from that just described. 
Azolla is a very curious genus, belonging to the fern allies. 
The species found in the Upper Nile is A. nilotica. The few 
species all float upon water, forming green or reddish patches, 
frequently several yards across, and they have creeping 
rhizomes which throw down roots towards the bottom of the 
pool or stream. ‘ The species occur from Australia and New 
Zealand as far as New York. One has been found in Western 
Africa by Vogel.’ A. filiculoides , found in California, often 
grows in densely crowded masses, the plants being usually 
much larger than those of the Eastern species. A. nilotica 
was got on the Shire River, in East Central Africa, by Dr. 
(now Sir John) Kirk, who noted it as ‘small, creeping’ (on 
the surface of the water), ‘ and sending down roots all along, 5 
and also by him on the Luabo River, ‘ floating, with Pistia 
and Trapal 
Ottellia , another genus of ‘ Sadd 5 plants named by Sir William 
Garstin, consists of ‘perennial herbs inhabiting the mouths 
of the Nile, Ganges, and Australian rivers, and eaten as 
potherbs in India. They are quite stemless.’ The size as 
well as the shape of the leaves varies much. The Indian 
plant is O. alismoides , Persoon. 
One other minor ‘ Sadd ’ plant is mentioned by Sir William 
Garstin, namely Aldrovanda. This is a genus of Droseraceae 
