naiadace;e. 25 



The flowers have never been found in Europe, but were observed 

 in abundance in Africa by Dr. Welwitsch, whose drawino^s liave been 

 copied on our plate, by permission of Dr. Seeniann. The magnified 

 figures of the barren plant are from sketches taken by Dr. Trimen.* 



Rootless Duckweed. 



German, Wurzellose Wasserlinsc. 



ORDER LXXVIL— NAIAD ACE ^ 



Perennial or more rarely annual aquatic herbs, submerged, sometimes 

 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 caucellate venation. Stipules often amplexi- 

 caul, rarely absent. Flowers perfect or unisexual, in the latter case 

 monoecious, rarely dioecious, sometimes arranged on a spadix, some- 

 times 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 seg- 

 ments. Female flowers without a perianth, or Avith 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, 3, or 4 stigmas. Fruit of as many small 

 indehiscent often subdrupaceous nuts as there are carpels, each nut con- 

 taining a single seed. Seed with a thin testa ; albumen none ; embryo 

 'trait or hooked ; radicle [ ointing towards the hilum or away fi'om it. 



GENUS /.—P OTA MO GET ON. 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 

 1-ovuled carpels, rarely reduced to 1 carpel ; stigmas subsessile or on 



* It is necessary to state that the sketches of Lcmna arrhiza, sent to Mr. Sowerby 

 by Dr. H. Trimen, were merely rough sketches, not detailed drawings. Unfortunately 

 the plate was not submitted to Dr. Trimen's inspection before printing, as he requested 

 it to be, so that he must not be considered responsible for the plate as it appears in 

 this work. — Ed. 



V'jL. IX. E 



