Najas. CXXXVII. NAlADACEiii. 593 



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

 only in the more slender habit, and less conii)lcte development of its parts. 



2. S P A R G A M U M. 



Gr. amapyafov, ii biiiul or fillet ; in rtHTcncc to tlio loiig, ribbon-like leaves. 



Spadix of flowers globose, cf Calyx 3 — 6-8epaled. V Calyx 3 — 6- 

 scpaled ; utricle turbinate, acuminate, 1 — 2-seeded. — Hoot %. Fls. 

 colleard in several dcnse^ rouiidish licads^ the sterile heads above the fertile. 



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



Lrs. trian,i,Milar at base, their sides concave; common flower-stalks branch- 

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

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

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

 arising above the stem, triangular towards the ba.'^e, 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. Nu(t.) 



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

 fioral oiics concave at base and erect ; siig. alw^ays 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— 2^' by 3", carinate 

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

 the simple styles conspicuous. Aug. 



3. S. NAT.4NS. Michx. Floating Burr Reed. 



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

 liead 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. NAIADACE^.— Naiads. 



Water plants, with cellular leaves and inconspicuous flowers. 

 Fls. perfect or mona-cious. Calyx '2— 4-sepaled or 0. 



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

 F?-. drj', indehiscent, 1-celied, 1-seeded. Seed pendulous. Albumen 0. 

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

 Conspectus of tlie Genera. 



\ solitarj-, diclinous, monandrous. "Saias 2 



ro. Flowers axillary, < 2 together, a sterile and fertile one Zannichellia. 3 



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



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



Spike I cylindric, covered with perfect, tetramerous flowers . Potamogeton. 5 



1. ZOSTfiRA. 



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



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

 perianth 0. J" 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 ; brariches 

 floating, simple; lrs. alternate, linear, entire, .sheathing at base, 1 — several feet 

 in length ; receptacle or spadi.c 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.— 'Zi- Habits aquatic, growing in the sea on sandv 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. vauiy to flow; hence Natj, or NatJcj, N>-mph of the waters ; from the habitat. 



Flowers often cf 9. c^ Calyx cylindric, 2-cleft ; stamen 1 (rarely 



