LEMNA.] LEMNACE^E. 425 



1. LEM'NA, L. DUCKWEED. 



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

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

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

 name. 



SECTION 1. Lem'na proper. Root single. Ovule 1, ^-anatropous. 

 Seed horizontal ; albumen copious. 



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

 Still waters, N. to Orkney ; ascends to 1,200 ft. in Derby ; Ireland ; Channel 



Islands ; fl. July. Frond ^-^ in., young sessile on the old, soon disconnected, 

 green above, paler beneath ; epidermal cells with flexuous walls. Spathe 

 unequally 2-lipped. Stamens 2, developed successively (each a male flower). 

 Style long. DISTRIB. Almost ubiquitous. 



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

 hastate persistent. Ivy-leaved Duckweed. 



Still waters, from Lanark and Banff southd. ; rare in Scotland ; local in Ire- 

 land ; Channel Islands ; fl. June- July. Frond |-| in., narrowed at the 

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

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

 grooved. DISTRIB. Europe, Siberia. 



SECTION 2. Telmatopha'ce, Schleid. (gen.). Root single. Ovules 

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



3. L. gib'ba, L. ; frond obovate or orbicular tumid beneath, stamens 

 2, utricle bursting transversely. 



Still waters, from Edinburgh and Lanark to Devon and Kent; local in Ire- 

 land ; fl. June-Sept. Frond J-| in., opaque, pale green, young sessile ; 

 cells beneath very large, epidermal with flexuous walls. DISTRIB. Europe 

 (excl. Greece), Siberia, N. Africa, America. 



SECTIONS. Spirode'la, Schleid. (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 Keut; local (if 



native) in Scotland ; Mid. Ireland. Frond J-| in., dark green above, purple 

 beneath, tracheae abundant ; epidermal cells with flexuous walls. Spathe 

 2-lipped. Stamens 2. DISTRIB. Europe (excl. Greece), Siberia, Madeira, 

 N. America. Flower unknown in Britain. 



2. WOLFF'IA, Hork. 



Fronds like grains of sand, rootless, oblong or subglobose, flattened 

 above, proliferous, cleft near the base. Flowers bursting through the 

 upper surface of the fronds. Spathe 0, Anthers sessile, 1-celled ; pollen 

 smooth. Ovary globose ; style short, stigma depressed ; ovule 1, erect, 



