XXI. APONOGETE^. 



805 



Potamogeton cfispus. 

 Young fruit (mag.)' 



P. crispus. Fruit cut 

 vertically and transversely (mag.). 



P. crispus. 

 Seed (mag.). 



P. er'upiu. 

 Embryo. 



LEAVES all submerged, or the upper floating, alternate or distichous or close 

 together, or rarely opposite, sessile or petioled, entire, filiform, linear, oval or oblong- 

 lanceolate, all similar, or the submerged narrower and deprived of a stomatiferous 

 epidermis ; stipules free, or joined to the base of the petiole, membranous, intrafoliar, 

 entire or emarginate. FLOWERS 5 or monoecious or polygamous, in a spike or 

 glomerate or solitary. PERIANTH of 4 herbaceous valvate sepals (Potamogeton); or 

 forming a membranous 3-toothed cup in the <? flowers, in the $ (Zannichellia) ; or 

 totally absent in the 5 flowers (Ruppia). STAMENS 4, sub-sessile, inserted on the 

 claw of the sepals (Potamogeton) ; or 2, sessile, hypogynous (Ruppia) ; or 1, stipitate 

 (Zannichellia, Althenia) ; anthers rounded, obtuse or apiculate and 3-celled, or oblong 

 and 1-celled (Althenia); pollen globose or oblong or arched, and very finely granular. 

 OVARIES 1-4-6, 1-celled, 1-ovuled; style elongate; stigma peltate or unilateral, 

 sessile ; ovule pendent, orthotropous or campylotropous. FRUIT sessile or stipitate, 

 indehiscent, coriaceous ; epicarp membranous ; endocarp hard, or opening into 2 

 valves at germination. SEED oblong; testa membranous; albumen 0. EMBRYO 

 inacropodous, antitropous or amphitropous, cotyledonary end arched or spirally 

 coiled. 



GENERA. 



Potamogeton. 

 Althenia. 



Grcenlandia. 

 Ituppia. 



Zannichellia. 



Spirillus. 



Potameee inhabit either stagnant water, sluggish streams, or brackish estuaries, or the shallow seas 

 of the cold and temperate regions of the globe. They are rare in the tropics. Zannichellia lives in 

 ditches in Europe and North America ; Althenia in the lagoons of the South of France and of Algeria ; 

 Ruppia in the muddy salt marshes in both continents. They are of no use to man. 



XXI. APONOGETE^E, Planchon 



Aquatic stemless HERBS with tuberous starchy feculent rhizomes. LEAVES 

 submerged or floating, petioled ; petiole enlarged and membranous at the base ; 

 blade linear, oval or oblong ; nerves 1-5, parallel, often united by transverse venules, 

 between which the cellular tissue is sometimes wanting, when the leaf is elegantly 

 latticed (Ouvirandra fenestralis) . FLOWEES white or pink, in a unilateral simple o: 



' 



