170 NAlAhACK.K. (I'ONDWKKl) FAMILY.) 



4. THALASSIA. Soland. 



Flowers dioecious. Sj)iitlio of tlu' sti-iilc tiowcr tcrmiiiatinf!^ the .scape, 

 2-ileft, tlie lobes ulituse. Sepals 3, oviile-ohlong, ohlnse. Autliers 9, sessile, 

 shorter than the eahx, eoniiivent. Fertile Howers unknown. — Marine herbs, 

 with linear sheatiiiiig leaves surrounding the central scape. 



1. T. testudinum, Koenig. Immersed; stem creeping; leaves 1° 

 long, the outer ones withering-persisteut. — iSiialluw water along the coast 

 of Florida. 



5. RUPPIA, L. Drrcu-GKASS. 



Fk)\vers perfect, naked, two or more on a slender spadix, enclosed in the 

 si)atiie-like sheatlis of the leaves, but soon long exserted. Stamens 2, closely 

 sessile: antherH-ells large, distinct. Ovaries 4, sessile, containing a single 

 suspended canijnlotr(>i)ous ovule. Stigma peltate. Achenium stalked, ob- 

 li(|uely ovate. Embryo pointed by the short plumule. — Salt-water herbs, 

 with ttliform branching stems, and alternate liuear or bristle-like sheathiug 

 leaves. 



1 . R. maritima, L. — In sliallow water, along tlie coast. May - August. 

 — Stems immersed, l°-3° long, mostly creeping at the base. Leaves filiform, 

 r-3' long, with dilated membr.auaceous sheaths. Fruiting peduncles l'-4' 

 long. Achenium ])ointeiL 



6. POTAMOGETON, Tourn. Poxdweed. 



Flowers perfect, spiked. Sej)als 4, roundish, valvate in the bud. Stamens 4, 

 ojijjosite tlie sepals: filaments sliort; anthers 2-celled. Ovaries 4, sessile. 

 Ovules ascending, campylotropous. Style short or none: stigma peltate. 

 Achcnia 1-4, compre.s.sed. Embryo curved or coiled. — Aquatic herl)S, with 

 immersed slender and jointed stems. Leaves sti))ulate, alternate and opposite, 

 either all immersed and commonly membranaceous, or tlie ujiper ones floating 

 and more rigid. Spikes peduncled, axillary and terminal. 



* Leaves all immersed and alike, 

 ■*- Leaves Jtliform. 



1. P. pectinatus, L. Stem flexuous; the branches diffusely forking, 

 disticlioiis ; leaves long, thickish, slightly channelled, approximate on the 

 branches; stipules small, united with the long and sheatiiing base of the 

 leaves; spikes slender, interrupted, on long filiform peduncles; achenium 

 dbovate, smoot;h, slightly compressed, keeled on the back. — Fresh or brack- 

 isii water. June - August. — Stems 2° - 3"^ long. Leaves 3' - 4' long. Spikes 

 1'- 2' long. 



2. P. pauciflorus, Pur.sh. Stem very slender, flattened, sparingly 

 branched; leaves scattered, thin, 3-nerved, sessile; stipules free from the 

 leaves, connate, sheathing ; spikes short-peduncled, 4 - 6-flowered, globo.se in 

 fruit ; achenium round-obovate, short-pointed, keeled and sinuate-toothed on 

 the back. — Shallow ponds, Georgia, and northward. July - August. — Stem 

 l°-2°long. Leaves 1'- 2' long. Peduncles J.'- 1' long. 



