54. Ceratophyllaceous Plants. Ceratophyllaceae

(254) Ceratophyllum - leaves whorled, 2-3 times furcately dissected.

(255) Callitriche - leaves opposite, entire.

55. Urticaceous Plants. Urticaceae

(256) Urtica - perianth of female flowers two-sepaled; stamens four.

(257) Parietaria - perianth of female flowers four-cleft; stamens four.

(258) Hunmlus - perianth of female flowers a mere scale; stamens five.

56. Polygonaceous Plants. Polygonaceae

(259) Rumex - perianth six-parted, the three inner segments becoming enlarged. (2G0) Oxyria - perianth four-parted, the two inner segments enlarged.

(261) Polygonum - perianth five-parted, the segments nearly equal.

57. Santalaceous Plants. Santalaceae

(262) Thesium - leaves alternate, entire, without stipules.

58. Euphorbiaceous Plants. Euphorbiaceae

(263) Euphorbia - flowers collected in heads, surrounded by a 4-5-toothed perianth-like involucre, enclosing several male flowers (each a single stamen, with jointed filament), and one female (a solitary three-celled stalked ovary). (264-) Mercurialis - herbs, with the male and female flowers separate, dioecious or monoecious.

59. Aristolochiaceous Plants. Aristolochiaceae

(265) Aristolochia - perianth tubular, very oblique; stameus six.

60. Trilliaceous Plants. Trilliaceae

(266) Paris - perianth of 8-10 narrow, spreading or reflexed segments.

61. Dioscoreaceous Plants. Dioscoreaceae

(267) Tamus - perianth of six segments.

62. Orontiaceous Plants. Orontiaceae

(268) Acorus - spathe (flower sheath) a continuation of the scape, and similar to the leaves, not convolute.

63. Typhaceous Plants. Typhaceae

(269) Typha - spadix (flower spike) cylindrical.

(270) Sparganium - spadix spherical.

64. Pistiaceous Plants. Pistiaceae

(271) Lemna - flowers monoecious; spathe urceolate; stamens 1-2.

65. Naiadaceous Plants. Naiadaceae

(272) Potamogeton - flowers perfect, in pedunculated spikes or heads.

(273) Zannichellia - flowers monoecious, axillary and sessile.

66. Hydrocharidaceous Plants. Hydrocharidaceae

(274) Stratiotes - stem scarcely any; leaves sword-shaped, tufted, radical, submerged; flowers polyandrous.

(275) Hydrocharis - stem root-like, bearing tufts of roundish floating leaves; flowers 9-12-androus.

(276) Anacharis - stems submerged, branched, with small opposite or whorled leaves; flowers minute, with nine stamens, or three styles.

67. Iridaceous Plants. Iridaceae

(277) Iris - perianth six-leaved, the three outer larger; stigmas three, petal-like, arching over the stamens.

(278) Gladiolus - perianth six-leaved, the divisions similar, with a somewhat oblique two-lipped arrangement, 68. Orchidaceous Plants. Orchidaceae.

* Anther single, the pollen simple, or consisting of granules in a slight state of cohesion.

(279) Listera - perianth ringent; lip deflexed, linear, or oblong, two-lobed; anther parallel with the stigma, enclosed in a hood.

(280) Epipactis - perianth patent; lip interrupted, the basal division concave, terminal one larger, with two projecting plates at its base above; anther terminal.

(281) Cephalanthera - perianth converging; lip interrupted, the basal division saccate, jointed to the recurved terminal one, which is without protuberances at the base; anther terminal.

** Anther single, the pollen cohering in grains or masses, which are indefinite in number and ivaxy.

‡ Lip spurred.

(282) Orchis - perianth ringent, hooded; lip three-lobed; pollenmasses with two glands enclosed in a common pouch; anther-cells converging at the base.

(283) Gymnadenia - as in Orchis, but the glands of the pollenmasses naked (without a pouch); anther-cells parallel at the base.

(284) Habenaria - perianth ringent, hooded; lip three-lobed or entire; glands of the stalks of the pollen-masses naked; anther-cells diverging at the base.

‡‡ Lip not spurred.

(285) Aceras - as in Orchis, except that the spur is wanting.