58 
that is split somewhat irregularly into 2-4 subulate stigmas. The 
mature carpel is solitary, sessile, ellipsoidal, with a crustaceous 
pericarp; seed conformed to the pericarp, and the embryo to the 
seed, the plumule and radicle immersed. Generally the raphe is 
distinctly marked on the seed. 
About 10 species are known, inhabitants of fresh water in 
tropical and temperate regions. Four species occur in North 
America, three of them belonging to the section Caulinia, as con- 
stituted by Willdenow, that is, species with the stems and backs 
of the leaves unarmed. 
I. NAIAS MARINA, L. Sp. Pl. 1015 (1753). 
N. major, АП. Fl. Ped. ii. 221 (1785). 
A dicecious plant with rather stout compressed stems com- 
monly armed with teeth half as long as their breadth. Leaves op- 
posite or in 3's, 6-18 lines long, about 1 line broad, with 6-10 
spine-pointed teeth on each margin, and frequently several along 
the back. Sheaths with rounded lateral edges, the type form 
without teeth. The teeth vary much in size and number. Some- 
times the stem is entirely naked, sometimes with only one or two 
teeth. The teeth on the leaf margins have a large basal prominence 
which often imparts a zig-zag appearance to the outline, this 
prominence being composed of several cells which buttress the 
yellow, 1-celled spine at the tip. Fruit large (2-214 lines long), 
the pericarp, as well as the seed, rugosely reticulate, tipped with 
a long, persistent style and 3 thread-like stigmas; seed not shin- 
ing. A polymorphous species, the extreme forms of which would 
hardly be recognized as belonging together. A. Braun enum- 
erates б forms, of which his variety Zhrendergü, with unarmed stem, 
the edges of the sheath furnished with 1-2 teeth, occurs in Florida 
(Dr. E. Palmer); and his variety termedia, or very nearly that, with 
long, naked internodes, leaves narrow, linear, each margin with 5 
or 6 large teeth, which are usually longer than the breadth of the 
leaf, without dorsal teeth, the sheath on each side with 1-4 teeth, 
and fruit nearly 3 lines long, occurs in Lake Cayuga, New York 
(Morong). 
Besides these the two following well-marked forms occur in the 
United States: 
