NAIADACEAE. 51 



style and 3 thread-like stigmas; seed not shining, rugose. In lakes, Cent. N. Y. to 

 Fla., west to Cal. Also in Europe. Summer. 



Naias marina grdcilis Morong. Internodes 2-8 cm. long, with a few teeth on the 

 upper part ; leaves scarcely 0.5 mm. wide, with 15-24 large teeth on the margins and a 

 few on the back ; sheaths with 2 or 3 teeth on each margin ; seed sculptured with about 

 25 rows of nearly square or irregularly oblong reticulations. Cent. N. Y. and Fla. 



Naias marina recurvata Dudley. Branches and leaves recurved ; leaves 6-12 mm. 

 long, narrow, with 2-4 large teeth on each margin and none on the back ; internodes 

 short, naked, or with 1 or 2 teeth; sheaths i-toothed on each side. Cayuga Marshes, 

 N. Y. 



2. Naias flexilis (Willd.) Rest. & Schmidt. Slender Naias. (I. F. f. 180.) 

 Stem slender, forking. Leaves linear, pellucid, acuminate or abruptly acute, 1-2.5 

 cm. long, 1-2 mm. wide, numerous and crowded on the upper parts of the branches, 

 with 25-30 minute teeth on each edge ; sheaths obliquely rounded with 5-10 teeth 

 on each margin ; fruit ellipsoid with .very thin pericarp, 2-4 mm. long, 0.5-1 mm. 

 in diameter ; style long, persistent ; stigmas short ; seed smooth, shining, straw- 

 colored, sculptured, though sometimes quite faintly, with 30-40 rows of nearly 

 square or hexagonal reticulations which are scarcely seen through the dark peri- 

 carp. In ponds and streams throughout nearly all N. Am. Also in Europe. Sum- 

 mer. 



Naias flexilis robiista Morong. Stem stout, few-leaved, 1-2 m. long ; internodes 

 elongated. Mass. to Mich, and Tex. 



3. Naias Guadalupensis (Spreng.) Morong. Guadaloupe Naias. (I. F. f. 

 181.) Stems nearly capillary, 0.3-0.7 m. long, widely branched from the base. Leaves 

 numerous, 12-18 mm. long, 0.5-1 mm. wide, acute, opposite or in fascicles of 2-5, 

 frequently recurved, with sheaths and teeth like those of N. flexilis but generally 

 with 40-50 teeth on each margin of the leaf ; fruit about 2 mm. long ; pericarp 

 dark and strongly marked by 16-20 rows of hexagonal or rectangular reticulations 

 which are transversely oblong ; seed straw-colored, not shining. In ponds and 

 lakes. Neb. to Or. and Tex., east to Fla. Also in tropical America. July-Sept. 



4. Naias gracillima (A. Br.) Morong. Thread-like Naias. (I. F. f. 182.) 

 Dioecious ; stem capillary, 15-40 cm. long, much branched, the branches alternate. 

 Leaves numerous, opposite or often fascicled in 3's-5's or more, setaceous, 2-5 cm. 

 long, usually with about 20 minute teeth on each margin ; sheaths auricled, with 6 

 or 7 teeth on each auricle, the teeth standing upon setaceous divisions of the sheath ; 

 stigmas very short ; fruit oblong-cylindric, I mm. long, 0.5 mm. in diameter, slightly 

 curved inwardly or straight, the pericarp straw-colored or purplish, marked by 

 about 25 rows of irregularly oblong reticulations ; seed not shining. In pools and 

 ponds, E. Mass. to Del. and Mo. July-Sept. 



5. ZOSTERA L. 



Marine plants with slender rootstocks and branching compressed stems. Leaver 

 2-ranked, sheathing at the base, the sheaths with infiexed margins. Spadix linear, 

 contained in a spathe. Flowers moncecius, arranged alternately in 2 rows on the 

 spadix. Staminate flower merely an anther attached to the spadix near its apex, 

 1 -celled, opening irregularly on the ventral side ; pollen thread-like. Pistillate 

 flower fixed on its back near the middle ; ovary 1 ; style elongated ; stigmas 2, 

 capillary ; mature carpels flask-shaped, membranous, rupturing irregularly, 

 beaked by the persistent style ; seeds ribbed ; embryo ellipsoid. [Greek, refer- 

 ring to the ribbon-like leaves.] About 6 species of marine distribution. Besides 

 the following one occurs in Fla. and one on the Pacific Coast. 



1. Zostera marina L. Eel-grass. Grass-wrack. (I. F. f. 183.) Leaves 

 ribbon-like, obtuse at the apex, 0.3-2 m. long, 2-8 mm. wide, with 3-7 principal 

 nerves. Spadix 2.5-6 cm. long ; flowers about 6 mm. long, crowded, usually from 

 10-20 of each kind on the spadix ; ovary somewhat vermiform ; at anthesis the 

 stigmas are thrust through the opening of the spathe and drop off before the anthers 

 of the same spadix open ; the anthers at anthesis work themselves out of the spathe 

 and discharge the glutinous stringy pollen into the water ; seeds cylindric, strongly 



