426 LEMNACEjE. [Wolffia. 



orthotropous. Utricle spherical, indehiscent. Seed oblique : albumen 

 fleshy, scanty. — Distrib. Europe local, Africa, America ; species 12. — 

 Etym. J. F. Wolff, a writer on Lemna. 



W. arrhi'za, JVimm. ; frond loosely cellular beneath. Lem'na Michel'ii, 



Schleid. 



Ponds, Essex, Middlesex, Kent, Surrey, probably common elsewhere. — The 

 smallest known flowering plant. Frond fa in. long, fa in. broad, young 

 solitary at the base of the old, soon detached ; epidermal cells with straight 

 walls. Flowers described from African specimens. — Distrib. Europe local, 

 from Holland southd. 



Order LXXXVI. ALlSMA'CEiE. 



Marsh or aquatic scapigerous herbs. Leaves chiefly radical, erect or 

 floating ; petiole sheathing. Flowers usually 2-sexual, usually panicled 

 or umbellate. Perianth inferior of 6 segments in two series. Stamens 

 6, 9, or more, hypogynous, filaments free ; anthers oblong. Ovary of 3, 

 6, or more carpels, free or subconnate ; styles short or 0, stigma terminal 

 simple or feathery ; ovules 1 or more in each cell, anatropous or campylo- 

 tropous. Fruit of indehiscent coriaceous carpels or follicles. Seeds 1 or 

 more in each carpel, testa coriaceous or membranous, albumen ; embryo 

 straight or hooked, radicular end thick, next the hilum. — Distrib. 

 All climates ; genera 10 ; species about 50. — Affinities. "With Naiadaccx. 

 — Properties unimportant. 



Tribe I. ALISME'-ffi. Sepals green. Petals usually large, fugacious. Ripe 

 carpels indehiscent. Ovules solitary, basal, or numerous in the inner 

 angle of the carpel. 



Flowers bisexual, whorled ; carpels free. Leaves erect 1. Alisma. 



Flowers bisexual, subsolitary ; carpels free. Leaves floating 2. Elisma. 



Flowers bisexual, whorled ; carpels connate. Leaves erect..3. Damasonium. 



Flowers unisexual, whorled; carpels free. Leaves erect 4. Sagittaria. 



Tribe II. BUTOME'-ffi. Petals and sepals similar. Ripe carpels dehiscent. 

 Ovules numerous, on branching parietal placentas 5. Butomus. 



1. ALISMA, L. 



Roots fibrous. Leaves erect. Flowers umbelled or whorled, bracteate, 

 honeyed. Sepals herbaceous. Petals deciduous, membranous, invo- 

 lute in bud. Stamens 6, filaments filiform ; anthers versatile, introrse, 

 Carpels many, free ; style ventral or terminal, short, stigma simple ; 

 ovules solitary, erect, campylotropous. Ripe carpels turgid or compressed, 

 ribbed, keeled, or grooved. Seed erect, testa very thin, raphe ventral ; 

 embryo hooked. — Distrib. Temp, and trop. ; species 10. — Etym. 

 doubtful. 



