yee my 
34 MISSOURI BOTANICAL GARDEN, 
herbarium, and in neither of these do I find any constant 
difference from Torrey’s species. In fact the descriptions 
of the two differ but slightly except in the number of ribs 
on the seed. This my study finds quite variable in the 
same pond though other characters are identical. There- 
fore I unhesitatingly place the American form heretofore 
credited to paucicostata under Torrey’s perpusilla. 
Specimens examined from Massachusetts (Clark) ; New York (Torrey, 
1829); New Jersey (Austin, 1869); Pennsylvania (Austin, 1860; Small, 
1891); Virginia (Coville, no. 85, 1890); South Carolina (comm. Torrey) ; 
Florida (Garber, 1869; Nash. no. 1591, 1894); Illinois (Engelmann, 1872; 
Schneck, no. 6, 1886; Eggert, 1896; Thompson, 1896; Hall); Missouri 
(Broadhead, 1864; Engelmann, 1867; Eggert, 1875; Bush. no. 584, 1896; 
Tracy, no. 19; Henney, 1896; Thompson, 1896); Arkansas (Eggert, 1896) ; 
Nebraska (Rydberg, no. 1723, 1893); Kansas (Norton. no. 532, 1895). 
++ ++ Fronds more or less oblong, thin, strongly 3-nerved. 
LEMNA PERPUSILLA Torr. var. TRINERVIS Austin, in Gray, 
Man. Bot. 479, 1867. [5th ed.] 
Fronds solitary or cohering in twos or threes, rarely 
more; oblong to obovate-oblong; very slightly convex 
above, flat beneath; more elongated and less unsymmet- 
rical than the species; apex more or less abruptly obtuse 
angled. Inflorescence and flowers as in the species. Fruit 
ovate, usually pointed by a rather long terminal style, 
nearly or quite symmetrical; seed ovate, erect or rarely 
slightly oblique. Otherwise partaking of the specific 
characters.— A characteristic variety of about the same 
territory as the type, growing with it or alone.— Plate 3 B. 
Commonly mistaken for Z. cyclostasa but readily dis- 
tinguished, even the sterile fronds, by the three prominent 
nerves. 
Specimens examined from New Jersey (Leggett, 1869); Illinois 
(Thompson, 1896); Tennessee (Gattinger, no, 2698, 1880); Missouri 
(Bush; Blankinship, 1889; Henney, 1896; Thompson, 1896); Louisiana 
(Dr. Hale, about 1830-40); Kansas (Hitchcock, no. 848, 1896); Indian 
Territory (Bush, no. 1834, 1895), 
+- + Fronds obscurely 1-nerved or nerveless; rootsheath unappend- 
aged. : 
++ Fronds thin, without papules; rootcap strongly curved, tapering 
to a small rounded apex. 
14 
