61 
4. Natas GRACILLIMA (A. Br.) Morong. 
N. Indica, Willd. var. gracillima, A. Br. by Engelmann in A. 
Gray, Man. Ed. 5, 681 (1868). 
Stems almost capillary, 6-15 inches high, much branched, the 
branches alternate; the whole aspect of the plant very graceful. 
Leaves numerous, opposite or often fascicled, 3-5 or more im the 
bundle, setaceous, %-2 inches long, usually with about 20 minute 
teeth on each margin. The marginal teeth are erect, with 1-celled 
yellowish spiny tips as in the other species, buttressed by 2, some- 
times 3 cells on the basal protuberance which give them the aspect 
of being 3 or more celled. Sheaths auricled, with 6 or 7 teeth 
on each auricle, the teeth standing upon setaceous divisions of the 
sheath. Dicecious. Styles bifid, the 2 stigmas very short. Fruit 
oblong cylindrical, about % line long by М line in diameter, 
slightly curved inwardly, the pericarp straw-colored or often pur- 
plish, marked by about 25 rows of irregularly oblong reticulations ; 
seed not shining. 
This plant differs very decidedly from JV. Indica, of which Braun 
made it a variety. It has more slender and longer leaves, smaller 
and fewer teeth, and different fruit from that of N. /ndica, which is 
described as ovate. It has sometimes been called JV. minor, a 
vcry different species, which is not known to occur in this country. 
In pools and ponds, still water, Ashland, Worcester, Winches- 
ter and Stoneham, Mass. (Boott, Morong); Albany, New York 
(Peck); Woodstown, New Jersey (Commons). Tidal mud of the 
Delaware, Camden, New Jersey, and Bristol, Pa. (Porter); Missouri 
(Engelmann.) (Plate LXVIII.) 
8. ZOSTERA, L. Sp. Pl. 968 (1753). 
Marine plants with slender rhizomes which root at the joints. 
Stems branching, compressed. Leaves distichous, sheathing at the 
base, the sheaths stipuliform, with inflexed margins. Spadix linear, 
contained in a spathe which is merely a sheath with overlapping 
flaps in the lower part of a leaf, or, as some botanists prefer to say, 
the spathe is on a long peduncle and has a long foliaceous ap- 
pendage at the top. Upon the spadix the two kinds of flowers 
are arranged alternately in two rows. Sterile flower merely an 
anther attached to the spadix near its apex, I-celled, opening 
