756 I. HTDEOCHAEIDE^. 



petioled, sometimes 1-2-pliyllous, smooth, or fringed on tlie dorsal nerve (Enhalus) ; 

 sometimes tubular, or longitudinally split on one side. — Flowers $ usually numerous 

 in a 1-2- phyllous spatlie, rarely solitary {Hydrilla, &c.), usually pedicelled, sometimes 

 furnisted -with a spathella or true bract. Perianth 6-pbyUous, 2-seriate ; outer 

 leaflets calycine, tubular, or sub-coherent at the base, imbricate or valvate in aesti- 

 vation ; inner leaflets petaloid, larger, contorted and folded in aestivation, very rarely 

 {VaUisneria). Stamens inserted at the bottom of the perianth, 3 opposite to the 

 sepals {Hyd/rilla, VaUisneria), or 6-9-12, several-seriate, some often imperfect ; fila- 

 ments free, or sub-monadelphous at the base, short, cylindric, compressed or clavate, 

 sometimes appendaged (flj/f^rocAam); anthers introrse, rarely extrorse {Hydrocharis), 

 2-celled, ovoid-globose or linear, adnate to the connective, dehiscence longitudinal ; 

 pollen smooth or papillose. Ovart rudimentary, occupying the centre of the flower. 

 — Flowers ? and 5 usually solitary ; spathe tubular, or split longitudinally, very 

 often sessile. Perianth superior ; limb 6-partite, 2-seriate ; outer segments caly- 

 cine, inner petaloid. Stamens inserted at the bottom of the perianth. Ovart 

 inferior, 1-celled, placentation parietal {TJdora, Anacharis, Hydrilla, VaUisneria, 

 Blyxa), or 6-8-9-celled {Stratiotes, Enhalus, Ottelia, Boottia, Limnobium, Hyd/rocharis); 

 style very short, or long and adnate to the perianth-tube; stigmas 3 in the 1-celled 

 ovary, 6 in the several-celled ovary, more or less deeply 2-fid, glandular-papillose on 

 the ventral side ; ovules numerous, ascending, orthotropous or anatropous. Fruit 

 submerged, various in formj usually longitudinally ridged, naked at the top, or 

 crowned by the persistent perianth, coriaceous, sub-fleshy, rupturing by decay in 

 the water, 1-celled, or more or less completely several-celled ; septa membranous, 

 opposite to the stigmas, and projected from the periphery towards the axis. Seeds 

 numerous, on pulpy parietal placentas which spread partially over the septa ; testa 

 membranous, tough, usually clothed with cylindric cells of a very elegant and often 

 spiral structure. Embryo exalbuminous, straight ; radicle reaching to the hilum ; 

 plumule usually very conspicuous, more or less lateral. 



[The following tribes are from Endlicher's ' Genera ' : — 



Tkibe I. ANACHAEiDEiE. — Caulescent. Leaves opposite or whorled. TJdora, Anacliaris, 

 Hydrilla, ApalantJie. 



Tkibi II. VALLISNEBIE.S!. — Stemless, scapigerous. Leaves all radical, linear. Ovary 1- 

 celled ; stigmas 3. VaUisneria, Blyxa. 



Tribe II. Stkatiotidb^, — Stemless, scapigerous. Ovary several-celled ; stigmas 6. 

 Stratiotes, Unlialus, Ottelia, Boottia, lAmtwhiv/m, Hydrocharis. — Ed.] « 



Hydrocharidea, placed by Brongniart in the class of Fluimles, with Butomea, Alismacece, Juncagineee, 

 Naiadece, &c., are separated from these families mainly by their inferior ovary. Though recognizing the 

 trivial value of this character, we have used it to distinguish Sydrocharidece, to avoid the alternative of 

 uniting in one family all the exalbuminous Monocotyledons, which, as sagaciously remarked by A. de 

 Jussieu, present a contiuuous series from the most simple type of flower, reduced to a stamen and a carpel 

 (Najas), to the most complex, represented by Hydrocharis. 



The few known species of Hydrocharis mostly inhabit fresh and still waters in temperate regions of 

 both worlds, or are maritime {JEnhalvs). Ottelia inhabits the Nile and rivers of tropical Asia and Aus- 

 tralia. VaUisneria is European, Asiatic, African, North American, and Australian ; (for its mode of ferti- 



