MONOCOTYLEDONOUS OR ENDOGENOUS PLANTS. 533 



flattened ut the sides, and surrounded with 5 prominent 

 ribs, beakless. Margins of shallow ponds. July and 

 August. Scajjes l'-4' high ; achenia black and shining. 



E. RADiCANS, Engelm. Leaves large, long-petioled, ovate, 

 cordate or truncate at the base, obtuse, 7-9-ribbed ; sca2M 

 elongated, prostrate, rooting and proliferous ; whorls sev- 

 eral, remote ; pedicels slender, spreading, or recurved ; sta- 

 onens about 20 ; style shorter than the ovary ; heads globose, 

 longer than the many-nerved sepals ; achenia very numer- 

 ous, short-beaked, ribbed, and slightly denticulate on the 

 back. (Alisma radicans, Nutt.) Swamps. July-Septem- 

 ber. Scape 2°-- i° long; leaves Z'-^' long ', flowers 8"-12" 

 wide. 



SAGITTARIA, L. Arrow Grass. 



Flowers monoecious, in a wliorled raceme, the upper 

 ones sterile ; sepals 3, persistent ; petals 3, imbricated in 

 the bud, witliering; stamens few or many ; ovaries crowded 

 in a globular head ; achenia flat, membranaceous, winged. 

 — Marsh or aquatic herbs, with scape-like stems, and 

 variousk-shaped nerved and reticulated sheathing leaves, 

 which are often without a blade ; flowers white, commonly 

 3 in a whorl from the axils of persistent bracts. 



* Filaments long and slender. 



S. FALCATA, Pursh. Tall ; leaves erect, rigid, broadly 

 lanceolate, acute at each end, pinnately nerved, on long and 

 stout petioles ; scape longer than the leaves, often branch- 

 ing above ; pedicels of the sterile flowers slender, longer 

 than those of the fertile ones ; bracts and sepals ovate, ob- 

 tuse, granular-roughened; stamens numerous with hairy 

 filaments ; achenia obliquely obovate, wing-keeled, strong- 

 ly beaked. (S. lancifolia, Michx.) Lakes and rivers. June- 

 September. Scape 2°-5° high; leaves l°-2° long; flowers 

 I'-li' wide. 



