Leuna. LEMNACE^. 245 



Order CVII. LEMNACE^E. Duhj. The Duckweed Tribe. 



Flowers monoecious, two (rarely one) sterile and one fertile, produced from the 

 margin of a flat frond, and bursting through a membranous urceolato si)athe, 

 without envelopes ; the sterile consisting of one or two stamens ; the fertile of 

 a one-celled ovary, which contains one or several amphitropous or orthotropous 

 ovules. Fruit an utricle. — Minute floating plants. Fronds destitute of proper 

 stem and leaves, and chiefly increasing by lateral offsets, with roots suspended 

 from the bottom of the frond, which are furnished with a calyptra or sheath- 

 like appendage at the extremity. 



The plants of this order arc generally regarded as a kind of reduced Aeaces:. 



1. LEMNA. Linn.; Emll. gen. 1668. DUCICS-MEAT. 



[Lemna is the Greek name of these little floating plants.] 



Sterile flowers two in each spalhe : filaments longer llian the style, curved. Style usually 

 elongated. — In other respects tlie character is that of the order. 



1. Lemna minor, Linn. Lesser Duchveed, or Duckmeat. 



Fronds obovate, roundish, thickish ; roots solitary. — Engl. hot. t. 1095; Linn. sp. 2. p. 

 970 ; MicJix. fl. 2. p. 163 ; Pursh, fl.l.p.22; Hook. fl. Lond. t. 120 ; Ell. sk. 2. p. 518 ; 

 Torr.fl. 1. p.^\ \ Bigel. fl. Bost. p. 334 ; Brongn. in Guill. arch. 2. p. 98. t. 12. /. 1 ; 

 Schleid. in Linncea, 13. p. 390 ; Beck, hot. p. 383; Darlingt. fl. Cest. p. 9 ; Kunth, enum. 

 3. p. 4. 



Fronds about 2 lines long, often several in a cluster, throwing down from the centre of 

 each disk underneath a long slender root which consists of a single fibre. Flowers not seen. 

 In the European plant the seeds are ampliiiropous and horizontal. 



Stagnant waters, covering the surface with a green mantle. I have no North American 

 specimens of this plant in flower, and it is therefore still uncertain whether it is the true 

 L. minor. According to Hooker, the young fronds constitute the L. arrhiza of French 

 botanists. 



2. Lemna perpusilla. Sfnallest Duckweed. 



Fronds obovate, thin ; roots solitary ; seed erect. 



Root a long solitary fibre. Fronds a line or a line and a half long, bright green on both 

 sides, grouped or single. Flowers bursting from a cleft in the side of the frond ; the 

 spathe cyalhiform. Stamens one or two in each spalhe, arriving at maturity in succession ; 

 the filaments filiform. Ovary roundish-ovoid, gibbous, obliquely acuminate, with a short 

 style which terminates in a simple stigma. Ovule single, anatropous, sessile at the base of 

 the ovary. Seed oblong, a little compressed, striate, erect ; the testa thick. 



