MONOCOTYLEDOI^OUS OR ENDOGENOUS PLANTS. 527 



130. PONDWEED FAMILY. Order, Naiadace^. 



Aquatic herbs, with slender jointed leafy immersed stems, 

 and perfect monoecious or dioecious floiuers, destitute of 

 floral envelopes, or with a scale-like calyx ; stamefis 1-4 ; 

 anthers 1-4-celled; ovary 1-celled, forming a 1-seeded 

 achenium in fruit; stigmas 1-4; seed without albumen; 

 embryo straight, curved, or coiled; leaves sheathing, or 

 with sheathing stipules; flowers commonly inclosed in a 

 spathe. 



SYNOPSIS. 



♦ Flowers moruxcions or dioecious. 



Stigma 2r-4. Flowers naked. Leaves opposite or whorled Naias, 



2. inclosed in a spathe. Leaves alternate Zostera. 



single peltate. Ovaries 4, from a cup-like involucre Zannichellia. 



** Flowers perfect. 



Fruit long-pedunded, utnbellate. Calyx and corolla none Ruppia. 



sessile, spiked. Calyx Cleaved Potamoqkton. 



NAIAS, L. 



Floiuers monoecious or dioecious, axillary, sessile, desti- 

 tute of calyx and corolla ; sterile flower monandrous, in- 

 closed in a spathe ; anther 4-celled, opening at the apex, 

 the filament lengthening ; fertile flower naked, the sessile 

 ovary pointed with the slender style ; stigmas 2-4, subu- 

 late; ovule erect; achenium minute; embryo straight; 

 radicle inferior. Stems filiform, forking; leaves opposite 

 or whorled, linear, dilated into a short sheath at the base ; 

 flowers solitary, minute. 



N. FLEXiLis, Rostk. Stem immersed (l°-2° long) ; leaves 

 3 in a whorl, narrow-linear, membranaceous, spreading, 

 minutely denticulate on the margins, the lower ones often 

 remote; stig7nas 3-4; achejiium elliptical, acute, smooth, 

 yellowish. (Caulinia flexilis, Willd.) In ponds and still 

 water. July and August, Leaves about 1' long. 



