Water plants with jointed stems, and sheathing stipules, or sheathing petioles. Flowers perfect or diclinous, naked or with a 2 to 4-parted perianth. Stamens definite. Ovaries free, sessile, 1-ovuled. Stigma simple, often sessile. Fruit indehis-cent. Seed without albumen, with a straight or curved embryo. Genera 9, species 60, in waters and marshes, salt or fresh in all countries.

Genera

* Flowers axillary, sessile, the staminate reduced to a single stamen (a).

a Fertile flowers reduced to a single pistil, with 2 or 3 stigmas. Lvs. opposite........

Najas.

1

a Fertile flowers with about 4 pistils in a cup, with as many stigmas............

ZANICHELLIA.

2

* Flowers spadaceous, or 2 to 20, sessile on a spadix or spike (b).

b Flowers monoecious, seated in 2 rows on the side of a linear, flat spadix.....

ZOSTERA.

3

b Flowers perfect, naked, 2 to 5, 4-mcrous; fruit raised on slender stipes......

Ruppia.

4

b Flowers perfect; perianth 4-sepaled; stam. 4. Pistils and achenia 4

POTAMOGETON.

5

1. NA'JAS. L. Water Nymph. (Gr.Order CXXXIV Naiadaceae Naiads 1907 to flow; hence Na Order CXXXIV Naiadaceae Naiads 1908 or

NOrder CXXXIV Naiadaceae Naiads 1909 , Nymph of the waters; from the habitat.) Flowers axillary, sessile, solitary, the Order CXXXIV Naiadaceae Naiads 1910 reduced to a single stamen; filament slender, often elongated, anther 4-valved, valves spreading; Order CXXXIV Naiadaceae Naiads 1911 perianth 0; style short, stigmas 2 or 3, subulate; fruit a little 1-seedecl, drupe-like nut. - Herbs entirely submersed, with opposite lvs. Fls. minute.

N. flexilis Rostk. St. filiform, caespitous, 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 thread-like knotted stems 6 to 12' long. Lvs. 1/2 to 1' long, 1/2" 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 summit. Aug. (N. Canadensis Mx. Fluviatilis, Pers.) β. fragims. 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;Order CXXXIV Naiadaceae Naiads 1912 stamen 1; filament elongated; Order CXXXIV Naiadaceae Naiads 1913 calyx monophyl-lous; corolla 0; ovaries 4 or more, each with a single style and stigma, and becoming in fruit an oblong, incurved, subsessile achenium. - Order CXXXIV Naiadaceae Naiads 1914 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. grass-like, 2 to 3' long, sassile. 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 6 ovaries which are free from the inflated, 1-sided, 2 to 3-toothed calyx. Jl, Aug.

3. ZOS'TERA, L. Sea Wrack. (Gr.Order CXXXIV Naiadaceae Naiads 1915 a girdle; alluding to its ribbon-like leaves.) Spadix linear, bearing the diclinous flowers in 2 rows on one side; perianth 0; Order CXXXIV Naiadaceae Naiads 1916 anther ovoid, sessile, opening lengthwise with conferroid pollen; pistils alternating with the stamens: style bifid; utricle 1-seeded. - Order CXXXIV Naiadaceae Naiads 1917 Maritime herbs. Stip. united into a sheath.

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 - several 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. -Order CXXXIV Naiadaceae Naiads 1918 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 Rappi, a German botanist.) FlowersOrder CXXXIV Naiadaceae Naiads 1919 , 2 together on a spadix or spike arising from the sheathing base of the leaves; perianth 0; stamens 4, each a 1-celled, sessile anther; ovaries 4, pedicellate, becoming in fruit 4 dry drupes or achenia. - Order CXXXIV Naiadaceae Naiads 1920 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 tails. July.

5. POTAMOGE'TON, Tourn. (Gr.Order CXXXIV Naiadaceae Naiads 1921 a river, Order CXXXIV Naiadaceae Naiads 1922 near.) Flowers Order CXXXIV Naiadaceae Naiads 1923 , on a spadix or spike arising from a spathe; calyx 4-sepaled; anthers 4, alternate with the sepals; ovaries 4; achenia 4, sessile flatted on one or two sides; seeds curved or coiled. - Mostly Order CXXXIV Naiadaceae Naiads 1924 , aquatic and submersed, only the flowers arising above the surface of the water. Spadix (or spike) pedunculate, 3 - 10-flowered. Lvs. stipulate, parallel-veined, lower alternate, the upper mostly opposite. Fls. small, greenish.

§ Leaves of two kinds; the floating, oval-elliptical, coriaceous petiolate, stipules free from the petiole, connate; subinersed leaves thin, (*)

* Floating leaves broader than the submersed ones, (a)

a Leaves all conspicuously stipulate......................................

Nos. 1, 2

a Leaves (the submersed ones) almost destitute of stipules.................

Nos. 3, 4

* Floating leaves smaller than the ample submersed ones............................

No. 5

§ Leaves of one kind only, all growing beneath the water's surface. (*)

* Stipules entirely free from the petiole or leaf, (a)

a Leaves lanceolate, petiolate or merly sessile..................................

Nos. 6, 7

a Leaves oval or oblong, broad and clasping at base........................

Nos. 8, 9

a Leaves linear, - Stems evidently compressed more or less............

Nos. 10,11

- Stems terete, very slender...................................

Nos. 12,13

* Stipules united with the sheathing base of the leaf......................................

Nos. 14, 15

1 P. natans L. Broad-leaved Pond-weed. Floating lvs. coriaceous, oblong, or elliptic-ovate, acute or obtuse or cordate at base, on long petioles, submersed ones linear-lanceolate, membranous, elongated, attenuated to petioles at base, lowest reduced to mere petioles; stipules connate, distinct from the petiole, elongated; spikes rather dense, shorter than the peduncles; fruit somewhat semi-globous, roughish, more or less carinato at the back. - A very common species, in slow waters or ponds, N. Eng. to Wis. St. slender, 1 to 3f long, according to the depth of the water, branched. Upper lvs. 2 to 4' long, about half as wide; petioles 2 to 8', submersed. Spike 1 to 2' long. Jl., Aug.