XXII. NAIADES. 807 



2-3-fid spike, at the top of an axillary scape, enclosed at first in a membranous 

 or coloured conical spathe. PERIANTH 0, or 2-3-phyllous, caducous or persis- 

 tent, sometimes accompanied by 10-15 distichous white thick and accrescent 

 bracts (Aponogeton}. STAMENS 6-18-20, hypogynous, sub-equal ; filaments subulate, 

 persistent ; anthers ovoid, basifixed, 2-celled ; pollen globose, or acutely elliptic. 

 OVARIES 3-5, flagon-shaped, sessile, 1-celled ; style continuous with the ovary, 

 oblique, and stigmatiferous on the inner face ; ovules 2-4-6, inserted a little to one 

 side at the bottom of the cell, ascending, anatropous. FRUIT a 1-2-seeded follicle. 

 SEEDS with membranous or sub-spongy testa ; albumen 0. EMBRYO oval or elliptic, 

 thick, compressed, radicular end inferior. 



GENERA. 

 * Aponogeton. * Ouvirandra. 



{Aponogeton is very closely allied to Potamea, and is distinguished chiefly by the bracts, hypo- 

 gynous stamens, and sub-basal ovules.] 



These genera belong to tropical Africa, India, and Madagascar. The name Ominmdra is taken from 

 the Madagascar language, in which the -word ouvirundrou signifies edible root, and is applied equally to 

 several species of Dioscorea ; the root omi is found bearing the same meaning throughout the islands of 

 the Southern Ocean. We have noticed elsewhere that the genus Spathiwn, of Loureiro, is a pynonym of 

 Satmmts. 



XXII. NAIADE^E. 



Marine or fresh-water annual or perennial HERBS. STEMS creeping or rooting, 

 branched. LEAVES alternate, distichous or opposite, often close together at the top 

 of the internodes, linear, 1-3-nerved, entire, or tip denticulate, base sheathing, 

 persistent, or jointed and caducous : sheath furnished with intravaginal free or connate 

 membranous stipules, sometimes accompanied by scales (Phucagrostis} ; spadices 

 usually solitary, sometimes several united in a common spathe, each furnished with 

 a 2-valved spathella, and bearing 3-6 g flowers (Posidonia}. FLOWERS $ (Posidonia}, 

 or monoscious (Zostera}, or dioecious (Najas, Phucagrostis}-, solitary (Phucagrostis}, or 

 sub-solitary (Najas}, or in axillary fascicles (Caulinia}, or united, 2 or more, on a 

 spadix contained in a foliaceous spathe. PERIANTH (Zostera, Phyllospadiar, Phuca- 

 grostis, Posidonia, &c.}', or tubular, membranous, 4-lobed (Caulinia, Najas}, or tubular, 

 denticulate (Halophila}. STAMENS 1 (Najas, Caulinia, Zostera, &c.}, or 2 (Phuca- 

 grostis}, or 43 (Posidonia}', filaments (Najas}, or very short, scale-like (Zostera}, or 

 dilated and aristate (Posidonia}, or geminate and coherent (Phucagrostis}; anthers 1- 

 celled (Zostera}, or 2-celled (Posidonia, Phucagrostis, &c.), or 4-celled (Caulinia, Najas}, 

 dehiscence longitudinal ; pollen usually confervoid (Zostera, Phucagrostis, &c.), or 

 globose (Najas, Caulinia}. OVARIES 1-2-4, distinct, 1-celled, usually 1-ovuled, 

 sometimes with C several-ovuled parietal placentas (Halophila, Lcmnopsis); stigmas 

 2 apiculate, or 3 filiform, sometimes jointed at the top of the style (Halophila, &c.), 

 rarely discoid and sharply branching (Posidonia} ; ovule pendulous and orthotropous 

 (Zostera}, or campylotropous (Phucagrostis, &c.), or ascending and anatropous 

 (Caulinia, Halophila, &c.). FRUIT usually a nut or utricle, sometimes a berry 

 (Posidonia}, inclehiscent, or opening more or less irregularly at germination. SEED 



