Order 134.— NAIAD ACB^E. 673 



often elongated, anther 4-valved, valves spreading ; $ perianth ; 

 style short, stigmas 2 or 3, subulate ; fruit a little 1-seeded, drupe-like 

 nut. — Herbs entirely submersed, with opposite lvs. Fls. minute. 



N. flexilis Rostk. St. filiform, csespitous, dichotomously branching ; lvs. opposite 

 or fasciculate in 3s, 4s or 6s, at the nodes, linear, obscurely denticulate, spreading, 

 1-veined. — A slender plant, Can. to N. J. and W. States, consisting of tufts of 

 tbread-likc knotted stems 6 to 12' long. Lvs. f to 1' long, -J-" wide, sessile and 

 sheathing at base. Flowers solitary, sessile, axillary, very small, the fertile ones 

 consisting of an oblong ovary tipped with a filiform style, with 2 to 3 stigmas at 

 aummit. Aug. (N. Canadensis Mx. Fluviatilis, Pers.) 



/?. fragilis. St. and lvs. rather rigid, the latter mostly opposite and recurved. 

 (Caulinia fragilis Willd.) 



2. ZANNICHEL'LIA, Micheli. Horn Pondweed. (In honor of Zan- 

 nichelli an eminent botanist of Venice.) Flowers axillary, usually both 

 kinds together ; & stamen 1 ; filament elongated ; $ calyx monophyl- 

 lous ; corolla ; ovaries 4 or more, each with a single style and stigma, 

 and becoming in fruit an oblong, incurved, subsessile achenium. — Q 

 Submersed, slender, branched, with entire, linear, scattered leaves. 



Z. palustris L. St. filiform, floating ; lvs. opposite, linear ; anth. 4-celled ; stig. 

 entire ; ach. toothed on the back. — In pools and ditches, N. States. St. round, 

 smooth, 1 to 2f long, branching, leafy. Lvs. gras3-like, 2 to 3' long, sessile. 

 Flowers issuing from axillary bracts, small, 2 together, a sterile and a fertile, the 

 former consisting of a single, naked, erect, yellowish-brown stamen, the latter of 

 4 to G ovaries which are free from the inflated, 1-sided, 2 to 3-toothed calyx. Jl, 

 Aug. 



3. ZOS'TERA, L. Sea Wrack. (Gr. ^oor^p, a girdle ; alluding to 

 its ribbon-like leaves.) Spadix linear, bearing the diclinous flowers in 

 2 rows on one side ; perianth ; $ anther ovoid, sessile, opening 

 lengthwise with conferroid pollen ; pistils alternating with the stamens : 

 style bifid; utricle 1-seeded. — U Maritime herbs. Stip. united into a 

 uheath. 



Z. marina L. St. trailing, throwing out tufts of fibrous roots at the joints ; 

 branches floating, simple; lvs. alternate, linear, entire, sheathing at base, 1 — 

 6everal feet in length ; receptacle or spadix linear, flat, pale green, 2' long, issuing 

 from a cleft in the base of the leaf, covered in front with a double series of naked 

 flowers. — U Aquatic, growing in the sea on sandy banks and shallows (Maine to 

 Ga.), and is thence washed upon the shore by the waves. Like other sea-weeds, 

 it is gathered for manure. Aug. 



4. RUP'PIA, L. Ditch-grass. (In honor of fiuppi, a German 

 botanist.) Flowers £ , 2 together on a spadix or spike arising from the 

 sheothing base of the leaves ; perianth ; stamens 4, each a 1-celled, 

 aessile anther ; ovaries 4, pedicellate, becoming in fruit 4 dry drupes or 

 achenia. — U Herb slender, branching, submersed except the flowers. 



R. maritima L A grass-like plant, salt water bays and ditches along the coast. 

 Stems several feet long, filiform, branched, floating. Leaves 1 — 2f long, linear and 

 Setaceous, with inflated sheaths at base, all immersed. The common peduncle is 

 contorted and spiral, and by winding and unwinding bears the spadix of naked, 

 green flowers on the surface of the water as it rises or falls. July. 



5. POTAMOGETON, Tourn. (Gr. ^o-a\i6q, a river, ye/rwv, near.) 

 Flowers £ , on a spadix or spike arising from a spathe ; calyx 4-sepaled ; 

 anthers 4, alternate with the sepals ; ovaries 4 ; achenia 4, sessile flat- 

 ted on one or two sides; seeds curved or coiled. — Mostly 71, aquatie 



43 



