Submerged or floating fresh-water or marine aquatic plants, or marsh herbs. Stems often elongated, slender, branched, jointed; sometimes short and almost wanting. Leaves very various, alto-gether submerged and translucent, or floating and opaque, or all; radical, sheathing at the base; stipules wanting or interpetiolar, page 746connate and sheathing. Flowers small and inconspicuous, usually green, hermaphrodite or unisexual, variously arranged. Perianth either wanting, or of 3–6 inferior segments valvate in bud. Stamens 1–6, hypogynous; anthers basifixed, erect, 1–2-celled. Ovary superior, of 1–6 distinct or more or less connate carpels, each 1-celled with usually a single erect or pendulous ovule; style long or short, stigma various. Fruit of 1–6 indehiscert nutlets or utricles, rarely drupaceous. Seed solitary, testa mem-branous; albumen wanting; embryo straight or curved, radicle unusually large.

A small order, dispersed over the whole world in marshy places, ponds, lakes, rivers, &c, also including some widely spread marine plants. Genera 16, species estimated at 120. The order cannot be said to have any important properties or uses. With the exception of Lepilœna, which is found elsewhere in Australia alone, all the New Zealand genera have a wide range in both temperate and tropical climates.

A. Flowers hermaphrodite. Perianth of 4–6 herbaceous segments.

Marsh plants with linear radical leaves. Flowers on erect scapes. Perianth-segments 6	1. Triglochin.
Aquatic plants with submerged or floating stems and leaves. Flowers in axillary or terminal spikes. Perianth- segments 4	2. Potamogeton.

B. Flowers unisexual [except in Ruppia). Perianth wanting or minute and hyaline.

* Stems and leaves filiform, submerged.

Flowers hermaphrodite, 2 or 3 on a peduncle greatly elongating in fruit. Perianth wanting. Stamens 2; anthers almost sessile	3. Ruppia.
Flowers unisexual, axillary, nearly sessile. Perianth wanting or female small and hyaline. Stamen 1, fila- ment slender	4. Zannichellia.
Flowers unisexual, axillary, nearly sessile. Perianth of 3 hyaline scales. Stamens 3; anthers sessile, cohering by their backs into a columnar mass	5. LbpilÆna.

** Stems creeping in sand or mud in salt water. Leaves ribbon-like, flat, nerved.

Flowers unisexual, enclosed in the membranous sheathing base of a floral leaf

6. Zostera.

1. Triglochin, Linn.

Perennial marsh herbs. Soots fibrous. Leaves all radical, fili-form or rush-like, flat or terete. Scapes slender, naked, erect, bearing a raceme or spike of small green hermaphrodite flowers. Perianth - segments 3 or 6, herbaceous, concave, deciduous. Stamens 6, inserted on the base of the perianth-segments; fila-ments very short; anthers didymous, extrorse. Carpels 6, distinct or more or less connate; stigmas penicillate; ovules solitary in page 747each carpel, basilar, erect, anatropous. Fruit of 3 or 6 free or connate coriaceous nutlets separating from a central axis. Seeds erect, cylindric or ovoid, terete or compressed; testa membranous; embryo straight.

About 12 species are known, spread through most temperate or subtropical regions, but especially plentiful in Australia. Both the New Zealand species are widely distributed.

Triglochin is often regarded as forming (with 3 other small genera) a distinct; order (Juncaginaceœ), but for the purposes of this work it appears moat convenient to merge it with the Naiadaceœ.

Scape 3–10 in. high. Fruit subglobose	1. T. striatum.
Scape 6–24 in. high. Fruit clavate	2. T. palustre.

2. Potamogeton, Linn.

Perennial aquatic herbs. Stems slender, simple or branched. Leaves wholly submerged and translucent, or floating and opaque, alternate or opposite, entire or toothed; stipules intrafoliar, free, or adnate to the petiole or base of the leaf. Flowers small, green, hermaphrodite, ebracteate, sessile in a dense spike on an axillary peduncle arising from a membranous spathe. Perianth-segments 4, small, herbaceous, concave, valvate. Stamens 4, inserted at the base of the segments; anthers sessile, 2-celled, extrorse. Carpels 4, sessile, distinct, 1-celled; stigma oblique, decurrent; ovules solitary, affixed to the inner angle of the cell, campylotropous. Eipe carpels or drupelets 4, small, coriaceous or spongy, ovoid or subglobose, obtuse or beaked by the recurved persistent stigma, 1-seeded. Seed curved, reniform; testa membranous; embryo with a large radicle and narrow incurved cotyledon.

A genus widely spread in the fresh or brackish waters of almost all tem-perate or subtropical regions, more rare in the tropics. Species variously esti-mated at from 40 to 100 or more, according to the different views of authors, extremely variable, and most difficult of discrimination. The New Zealand forms have never been carefully sought for, and in all probability other species will be added to those described herein.

A. Floating leaves more or less coriaceous, with a broad long-petioled lamina, different in shape from the membranous submerged ones. Stipules free.

Floating leaves 2–4 in., biplicate at the base. Submerged leaves wanting or reduced to phyllodes. Fruit large, ⅙ in. long, keeled on the back when dry	1. P. natans.
Floating leaves 1–3 in., not plicate at the base. Sub-merged leaves few, linear-lanceolate. Fruit small, 1/12–1/10 in., rounded on the back	2. P.polygonifolius.
Floating leaves ¾–1¾ in. Submerged leaves numerous, 2–4 in. Fruit small, 1/10 in., keeled on the back when dry	3. P. Cheesemami.

B. Leaves all submerged and uniform, sessile, membranous.

Leaves 1–4 in. by ⅛–¼ in., linear-ligulate, obtuse; stipules free, lacerate. Spike dense	4. P. ochreatus.
Leaves 2–4 in. by 1/20–1/15 in., very narrow-linear or filiform; stipules adnate. Spike interrupted	5. P. pectinatus.

3. Ruppia, Linn.

Slender submerged much-branched herbs, usually growing in brackish water. Leaves alternate or opposite, filiform, with broad sheathing bases. Flowers minute, hermaphrodite, 2 or more on a spike, at first enclosed in the membranous leaf-sheath, but after flowering the filiform peduncle elongates greatly, and is either straight or spirally coiled. Perianth wanting. Stamens 2, opposite; filaments very short; anthers 2-celled, the cells distinct, opening outwards. Carpels 4; stigma sessile, peltate; ovule solitary, pendulous from the apex of the cell. Fruiting carpels stipitate, obliquely ovoid, obtuse or beaked. Seed uncinate; testa, membranous; embryo with a large thick radicle and small incurved cotyledon.

A genus of either one variable species or of several closely allied ones, common in brackish waters in almost all temperate or subtropical countries.

4. Zannichellia, Linn.

Slender submerged water-plants; stems filiform, branched. Leaves usually opposite, filiform, sheathing at the base; sheaths stipular. Flowers minute, axillary, monœcious, a single male and female enclosed in the membranous leaf-sheaths. Male flower: Perianth wanting. Stamen 1; filament short at first, elongating as the flower expands; anther 2–3-celled, linear, basifixed, page 752cells dehiscing laterally, connective produced, apiculate. Female flower: Perianth short, cupular, hyaline. Carpels 2–6, sessile; styles long or short; stigma large, obliquely peltate, crenate; ovule solitary, pendulous, orthotropous. Ripe carpels usually 3 or 4, sessile or stalked, curved, oblong or oblong-reniform, slightly compressed, tubercled or crenate or smooth on the back, beaked by the projecting style. Seed pendulous; testa membranous; embryo cylindric, the cotyledonary end bent into a short coil.

An almost cosmopolitan genus of 4 or 5 closely allied species, probably all forms of one.

5. LepilÆna, J. Drummond.

Very slender submerged water-plants; stems filiform, branched. Leaves alternate or the floral ones opposite, filiform, sheathing at the base; sheaths broad, stipular. Flowers minute, axillary, diœcious or rarely monœcious, solitary within the dilated sheathing bases of a pair of floral leaves. Male flowers shortly pedicelled. Perianth very minute, of 3 hyaline scales. Anthers 2 or 3, united by their backs and forming a solid column resembling a single anther; each anther 2-celled, dehiscing longitudinally. Female flowers sessile or shortly pedicellate. Perianth of 3 hyaline segments longer or shorter than the carpels. Carpels 3, distinct, sessile or shortly stipitate, narrowed into a short or long style; stigma oblong or spathulate; ovule solitary, pendulous. Ripe carpels usually 3, oblong, coriaceous, indehiscent, tipped by the persistent style. Seed oblong; testa membranous; embryo with a thick obtuse radicle and tapering involute cotyledonary end.

A small genus of 4 species, 3 of which are Australian, one of them said to extend to New Zealand; the remaining one is endemic in New Zealand. In Engler's "Naturlichen Pflanzenfamilien" the genus is merged with the Mediterranean Althenia.

page 753

Leaf-sheaths narrow. Anthers 3, connate into a column. Stigma oblong-clavate	1. L. Preissii.
Leaf-sheaths broad. Anthers 2 (or 1?). Stigma very large, flat, deeply fimbriate	2. L. bilocularis.

6. Zostera, Linn.

Marine submerged plants. Rhizomes slender, branched, creeping and rooting at the nodes, often matted. Stems short, slender, leafy, compressed. Leaves distichous, alternate, narrow-linear, grass-like, 1–5-nerved, sheathing at the base; sheaths stipuliform with inflexed margins. Flowers monœcious, the males and females-placed alternately upon one face of a narrow spadix enclosed within the dilated membranous base of a leaf. Perianth wanting. Male flowers: Anther solitary, sessile, oblong, cylindric, curved, 1-celled dehiscence longitudinal; pollen confervoid. Female flowers: Carpel solitary, laterally attached above the middle, narrowed into a short subulate style; stigmas 2, capillary; ovule pendulous from the apex of the cell. Ripe carpel oblong, membranous, bursting irregularly. Seed pendulous; testa membranous, often striated; embryo large, deeply grooved, the linear incurved cotylecdonary end sunk in the groove.

Three or four closely allied species are known, found in shallow water on the shores of most temperate regions.

Leaves 3–9 in. x 1/16–1/10 in., truncate or notched at the tip. Spadix with transverse appendages, one folded over each carpel	1. Z. nana.
Leaves 9–18 in. x 1/10–⅙ in., rounded at the tip	2. Z. tasmanica.