LEMNACEiE. (DUCKWKED FAMILY.) 479 



from a cleft in the margin towards the base, and at length stipitate ; the tissue 

 abounding with bundles of acicular rhaphides, as in Araceas. (An old Greek 

 name, of uncertain meaning.) 



§ 1 . LEMNA, Schleiden. Root single : ovule one, half-anatropous or orthotropous. 



1. L. trisiilca, L. Fronds oblong -lanceolate from a stalked base, thin, dentic- 

 ulate at the tip (j'-f long), proliferous from one or both sides; seed half-ana- 

 tropous. — Ponds and springy places ; immersed and living through the winter, 

 usually several generations remaining connected. Flowers found, for the first 

 time in this country, by C. M. Booth, Rochester, New York. (Eu.) 



2. L. Torreyi, Austin, n. sp. Fronds oblong or obovate-oblong , usually some- 

 what falcate. (l"-24" long), thin, faintly 1 -nerved, cavernous to the apex, pale 

 green both sides, commonly in groups of 4 - 8 ; utricle elongated-ovate, pointed by 

 the long style, flattish, usually half the length of the frond ; seed oblong and rather 

 abruptly expanded below the middle, unequally cordate at the base, orthotropous, 

 very obtuse, partly striate when dry ; testa fleshy, loosely adhering to the thick- 

 ish and solid inner coat; operculum distinctly apiculate ; albumen very scanty (a sin- 

 gle layer of cells). — Pools, New Jersey (fertile) to Missouri and southward. 



3. L. perpusilla, Torr. Fronds obovate or roundish-obovate, oblique ( I " - l£" 

 long), obscurely 3-nerved, grouped in circular patches (of 4 -8) ; utricle ovate 

 and at length oblique, tipped with a rather long eccentric style ; seed ovate or oval, 

 obtuse, oblique in the utricle, orthotropous, delicately many-striate when dry ; testa 

 coriaceous, solid, firmly attached to the very thin inner coat ; operculum scarcely 

 apiculate ; albumen abundant. — New York to Wisconsin and southward : often 

 fertile. — Var. trinervis, Austin. Fronds larger, distinctly 3-nerved, thin ; utricle 

 ovate, pointed with a rather long style ; seed ovate, acutish, mostly straight, 

 unequally cordate. — New York and Penn. (fertile) to Wisconsin. 



4. L. minor, L. Fronds obovate or elliptical-olovate, thickish (V- 2" long), 

 often grouped and short-stalked, obscurely 3-nerved ; utricle short-urn-shaped and 

 tipped with a short style ; seed oval or ovate, half-anatropous, horizontal, parallel with 

 the margin of the frond. — Stagnant waters : common : rare in flower. (Eu.) 



Var. obscura, Austin. Fronds obovate, convex on both surfaces, often 

 purple underneath. — New York to Virginia : sterile. 



Var. orbicillata, Austin. Fronds nearly orbicular, flat above, convex and 

 dark purple underneath, proliferous on very short included stalks. — New York 

 to Wisconsin and southward : sterile. — This and the preceding variety have been 

 taken for L. gibba by American authors. 



§ 2. SPIRODELA, Schleiden. Roots several in a cluster: ovules 2, anatropous. 



5. L. polyrrhiza, L. Fronds round-obovate (2" -4" long), thick, purple 

 and rather convex beneath, dark green above, palmately (mostly 7-) nerved. — 

 Very common in ponds and pools ; not found here in blossom. (Eu.) 



§3. TELMAT6PHACE, Schleiden. Roots single: ovules and seeds 2 - 7 , ana- 

 tropous : albumen hardly any in the mature seed. 



6. L. gibba, L. Fronds obovate or almost orbicular (\^"-3" long), 

 nearly flat above, much thickened and cavernous-spongy underneath (almost 

 hemispherical), proliferous on short and very fragile stalks, therefore seldom 



