Najas. CXXXVII. NAIADACEiE. 523 



the same situations with the former. A well marked variety, but differing 

 only in the more slender habit, and less complete development of its parts. 



2, SPARGANIUM. 



Gr. (Tirapyai/ov, a band or fillet ; in reference to the long, ribbon-like leaves. 



Spadix of flowers globose. cT Calyx 3 — 6-sepaled. 9 Calyx 3 — 6- 

 sepaled ; utricle turbinate, acuminate, 1 — 2-seeded. — Root %. Fls. 

 collected in several deme^ roundish heads^ the sterile heads above the fertile. 



1. S. ERECTUM. (S. ramosum. Smith.) Burr Reed. 



Lrs. triangular at base, their sides concave ; commo7i flower-stalks branch- 

 ed; stig. 2, linear. — Grows in pools and ditches, where it is conspicuous among 

 other reedy plants for its globular burrs of flowers. Stem 1 — 2f high, flexuous, 



round, with a few branches above. Leaves J — 2f long, 4 8" wide, linear' 



arising above the stem, triangular towards the base, and sword-form upwards,' 

 tapering, but obtuse. Heads of flowers light green ; fertile ones 2—5, the low- 

 est generally raised on a short, axillary stalk ; sterile ones above, more numer- 

 ous, smaller, sessile. Aug. 



2. S. SIMPLEX. Smith. (S. Americanum. Nutt.) 



Lower lis. equal with, or exceeding the stem, which is nearly simple, 

 floral ones concave at base and erect ; stig. always simple, ovate oblong, oblique, 



scarcely more than half the length of the style.— Ponds and lakes. Stem 1 2f 



high, simple or divided at base. Leaves mostly radical, 1 — 2jf by 3", carinate 

 at base. Fertile heads sessile, generally 3, below the several barren ones, with 

 the simple styles conspicuous. Aug. 



3. S. NATANs. Michx. Floating Burr Reed. 



Lvs. floating, flat ; common flower-stalk simple ; stig. ovate, very short • 

 head of sterile fls. subsolitary. — Lakes and pools, U. S. and Brit. Am. Stem 

 long and slender, and, with the leaves, floating upon the surface of the water. 

 Leaves thin and pellucid. Heads of fertile flowers axillary, generally 2 

 mostly sessile. Sterile cluster terminal. Aug. ' 



Order CXXXVII. NAIADACEJE.— Naiads. 



Water plants, with cellular leaves and inconspicuous flowers. 

 Fls. perfect or mono'cious. Calyx 2— 4-sepaled or o. 



Sta. definite. Ovaries l, or 2—4, free, 1-ovuIed. Stigma simple, often sessUe. 

 Fr. dry, indehiscent, Icelled, 1-seeded. Seed pendulous. Albutnen 0. 

 Genera 9, species 16, in waters and marshes, salt and fresh, in nearly all countdes. 

 Conspectus of the Genera. 

 S solitary, diclinous, monandrous. .... Najas 3 



("0. Flowers a.villary, { 2 together, a sterile and fertile one Zannichcllio. 3 



1 short, 2flowered, borne on a long, tortuous peduncle, Ruppia- 4 



1 linear, bearing the monoecious flowers in a double row. Zostera. 1 



Spike Lcylindric, covered with perfect, tetramerous flowers Potamogeton. S 



1. zostEra. 



Gr. ^(xXTTtip, a girdle ; alluding to its ribbon-like leaves. 



Spadix linear, bearing the separated flowers in 2 rows on one side ; 

 perianth 0. c? Anther ovoid, sessile, parallel to the ovary. 9 Ova- 

 ries 2, ovoid ; style bifid ; utricle 1-seeded. 

 Z. MARiNA. Sea Wrack-grass. 



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. — If. Habits 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. 



2. NAJAS. 

 Gr. vao3, to flow; hence Nais, or NaiJtf, Nymph of the waters ; from Uie habitat. 



Flowers often c? 9 cT Calyx cylindric, 2-cleft ; stamen 1 (rarely 



