NATURAL OKDEKS. 
28? 
margin of the frond, inclosed in a spatha Without a spadix. 
Stamens 1 or 2. Ova/ry 1-celled ; ovules 2 or more. Fmit 
membraneous or capsular. (See Plate YIII., Fig. 2.) 
Genera. — Pistia, Lemna. 
535. i^MABACEM, the jPond-weed Trihe, — Water plants, leaves 
very cellular, with parallel veins. Flowers inconspicuous, some- 
limes perfect. Perianth of 2 or 4 pieces, or wanting. Stamens 
definite, hjpogynous. Ovaries 1 or more ; ovule solitary. Fruit 
dry, usually indehiscent. Seed erect or pendulous, exalbumi 
nous ; embryo straight or curved. 
Genera. — Potamogeton, Najas, Ruppia, Zosteta, Zannichellia. 
536. Alismace^, the Water-Plantain Tribe. — Floating or 
swamp plants., usually with a creeping, fleshy rhizoma. Leaves 
with parallel veins. Flowers regular, perfect, or polygamous, 
usually in racemes or panicles. Sepals 3. Petals 3. Ovaries 
superior, several, 1-celled. Frvjit dry, 1 or 2 seeded. Seeds 
straight or curved, destitute of albumen ; embryo shaped like a 
horse-shoe. 
a. Properties : some are acrid, others have edible rhizomes. 
Genera. — Alisma, Sagittaria. 
537. Sub-order tTtJNcAGiNE^. Seed and embryo straight. 
Genera. — Triglochin Scheuchzeria. 
538. Hydrochaeidace^, the Frog-bit Tribe. — Aquatic herbs. 
Leames parallel-veined, sometimes spiny. Flowers dioecious < »t 
polygamous, inclosed in spatha. Sepals 3, herbaceous. PetaU 
Stamens definite or indefinite. Ovary adherent, 1 or many- 
celled ; ovules frequently attached to parietal placentBe. Fruit 
dry or succulent. Seeds numerous, exalbuminous ; embryo 
straight. 
Genera.— Uddira, Vallisfileria, fiydrocharis. 
539. BuRMANNiACE^. — Herbs with radical leaves. Perianth 
colored, tubular, 6-cleft, the three outer (caly5f) sometimes keel- 
ed at the back, the 3 inner (petals) minute. Stamens 3, oppo- 
site the petals. Ovary adherent, 1-3-celled, with 3 placentso 
Fruit a capsule. Seeds innumerable, minute, without albumen 
G^iNtTs.— Apiteria. 
540. Okchidace^, the Orchis Trihe. — Herbs or shHtbs^ With 
fibrous or tuberous roots. Stem simple or wanting. Leawes 
mostly radica<^, sheathing, cauline ones sessile. Flowers irregu- 
lar, bracted, commonly in a spike, or racemose, or panicled, 
Beldom solitary. Pefrianth 6-parted, 3 divisions external, 3 in- 
ternal ; a lower one in the form of a lip (labellum), often spur- 
red. Stamens opposite the sepals, cohereut "with the style 
(com^posing the column) ; poll&n powdeiy, or cohering in waxy 
