NAIADACE®. 25 
from all the other species in having no roots, and the bud bursting 
from the base of the parent frond. 
The flowers have never been found in Europe, but were observed in 
abundance in Africa by Dr. Welwitsch, whose drawings have been 
copied on our plate, by permission of Dr. Seemann. The magnified 
figures of the barren plant are from sketches taken by Dr. Trimen. 
Rootless Duckweed. 
German, Wurzellose Wasserlinse. 
ORDER LXXVII.—NATADACE /. 
Perennial or more rarely annual aquatic herbs, submerged, some- 
times with the uppermost leaves floating or rising above the water, 
which the flowers also usually do at the time the pollen is shed. 
Rootstock often creeping, slender, rarely with tuberous enlargements. 
‘Stem more or less elongated. Leaves alternate, rarely all, or more 
often the upper ones opposite, usually entire, stalked or sessile or 
sheathing at the base, with parallel or cancellate venation. Stipules 
often amplexicaul, rarely absent. Flowers perfect or unisexual, in 
the latter case monecious, rarely dicecious, sometimes arranged on a 
spadix, sometimes solitary or crowded in the axils of the leaves. 
Perfect flowers with a subherbaceous 4-leaved perianth, or naked. 
Male flowers usually destitute of perianth, but sometimes of 3 or 4 
scale-like perianth segments. Female flowers without a perianth, or 
with a campanulate membranous perianth. Stamens 1, 2, or 4; anthers 
1- or 2- rarely 4-celled, frequently sessile or subsessile. Ovary free 
from the perianth, of 2 or 4 distinct carpels (rarely of 1, 3, 5 or 6 
carpels), each carpel with a single ovule and a separate stigma, or 
if a single carpel with 1 ovule, and generally with 2, 5, or 4 stigmas. 
Fruit of as many small indehiscent often subdrupaceous nuts as there 
are carpels, each nut containing a single seed. Seed with a thin testa; 
albumen none; embryo straight or hooked; radicle pointing towards 
the hilum or away from it. 
GENUS I—POTAMOGETON. Linn. 
Flowers numerous, perfect, sessile, disposed all round a stalked 
axillary or terminal stalked spadix, issuing from a sheathing bract. 
Perianth single, of 4 herbaceous leaves (sepals) with short claws. 
Stamens 4, inserted in the claw of the perianth leaves; filaments very 
Short; anthers 2-celled. Ovary free, of four separate 1-celled and 
l-ovuled carpels, rarely reduced to 1 carpel; stigmas subsessile or on 
VOL. IX. E 
