LEMNA.] LEMNACE^E. 395 



ORDER XI. LEMNA'CEJE. 



Minute floating solitary or fascicled green fronds, rootless or with 

 capillary simple roots, propagated by budding from marginal clefts, and 

 by autumnal hybernating bulbils, rarely by seed ; vascular tissue or 

 rudimentary ; roots tipped by a membranous sheath. Flowers rarely 

 produced, most minute, 1-3 in a spathe. Perianth 0. Stamens 1-2 ; 

 anthers 1-2-celled, dehiscence transverse ; pollen spherical. Ovary 1- 

 celled ; style short, stigma truncate or funnel-shaped ; ovules 1-7, ortho- 

 tropous anatropous or ^-anatropous. Utricle bottle-shaped. Seeds 1 or 

 more, testa coriaceous, inner coat thickened and discoid over the radicle, 

 albumen fleshy or ; embryo axile, straight, stout, cylindric. DISTRIB. 

 All standing waters; genera 6; species about 20. AFFINITIES. With 

 Pistiacece, Naiadece, and Aroidece. PROPERTIES 0. 



Frond with 1 or more capillary roots 1. Lemna. 



Frond rootless 2. Wolffia. 



1. LEMNA, L. DUCKWEED. 



Fronds with roots. Flowers in marginal clefts of the frond. Stamens 

 1-2, filaments slender ; anthers 2 -celled, didymous ; pollen muricate. 

 Ovules 1-7. DISTRIB. All latitudes; species 12. ETYM. The Greek name. 



SUB-GEN. 1. Lem'na proper. Hoot single. Ovule 1, ^-auatropous. 



Seed horizontal ; albumen copious. 



1. Ii. mi'nor, L. ; frond obovate or oblong slightly convex below. 



Still waters ; fl. July. Annual. Frond fe-% in., young sessile on the old, soon 

 disconnected, green above, paler beneath ; epidermal cells with flexuous 

 walls. Spatlie unequally 2-lipped. Stamens 2, developed successively (each 

 a male flower?), filaments slender. Style long. DISTRIB. Almost ubiquitous. 

 2. Ii. trisul'ca, L.; frond flat obovate-lanceolate, tip serrate, young 



hastate persistent. Ivy-leaved JJuckweed. 



Still waters, from Fife and Forfar to Devon and Kent, but rare in Scotland ; 

 local in Ireland ; fl. June-July. Frond |-^in., submerged, narrowed at the 

 base, without epidermis, proliferous on one or both sides ; young fronds, 

 numerous placed crosswise to the old. Style very short. Testa, rough, 

 grooved. DISTRIB. Europe, Siberia. 



SUB-GEN. 2. Telmatopha'ce, Schleiden (gen.). Root single. Ovules 

 2-7, erect, anatropous. Seeds erect ; albumen scanty or 0. 



3. L. gib ba, L. ; frond obovate or orbicular tumid below, stamens 2, 

 utricle bursting transversely. 



Still waters, from Fife to Devon and Kent, E. of Scotland only ; rare and 

 local in Ireland; fl. June-Sept. Frond ^- in., opaque, pale green, young 

 sessile ; cells beneath very large, epidermal with flexuous walls. DISTRIB. 

 Europe, Siberia, N. Africa, America. 



SUB-GEN. 3. Spirode'la, Schleiden (gen.). Roots many. Ovules 2, erect, 

 anatropous. Fruit unknown. 



4. L. polyrhi'za, L. ; frond broadly obovate plano-convex 7-nerved. 

 Ponds and ditches from Lanark and Edinburgh to Devon and Kent southwards ; 



