66 LEMNACEAE. 



diameter, the berries green. — Common, in swamps and low meadows. — Spr. 



— Skunk-cabbage. 



4. ORONTIUM L. Swamp herbs. Leaves with relatively narrow blades. 

 Spadix terminal, elongate, subtended by the thin spathe, the scape pliable, soon 

 weak. Flowers perfect. Perianth of 4-6 scale-like members (6 below, 4 above). 

 Fruits not immersed. 



1. O. aquaticum L. Eootstock deeply buried. Leaf-blades oblong or elliptic, 

 1-3 dm. long : spadix golden-yellow, 2-6 cm. long. — Eather rare, in swamps, 

 ponds or streams. — Spr. — Golden-club. Bog-torches. Fire-leaf. 



5. ACORUS L. Swamp or meadow herbs with aromatic rootstoeks. Leaves 

 with linear blades. Spadix lateral, elongate, at the base of the linear spathe. 

 Flowers perfect. Perianth of 6 concave members. Fruits crowded. 



1. A. Calamus L. Eootstock horizontal: leaves 5-20 dm. tall: scape resembling 

 the leaves : spathe erect : spadix yellowish, 3-8 cm. long. — Common, in low 

 grounds and swamps. — Spr. and sum. — Calamus. Sweet-flag. 



Family 2. LEMNACEAE. Duckweed Family. 



Floating herbs, consisting- chiefly of very small, often minute, fleshy 

 structures, sometimes with 1 or several roots. Propagative pouches 1 or 

 2 in each body. Flowers monoecious, one or two staminate and one 

 pistillate in a propagative pouch. Staminate flowers consist of 1 stamen. 

 Pistillate flowers consist of 1 carpel. Fruit a utricle. 



Root solitary, without a flbro-vascular bundle : plant-body inconspicuously nerved. 



1. Lemna. 

 Roots several, each with a flbro-vascular bundle : plant-body con- 

 spicuously nerved. 2. Spirodela. 



1. LEMNA L. Plant-body disk-like, inconspicuously nerved. Anther-sacs 

 opening transversely. Utricle somewhat flattened, often ribbed. — Sum. — 

 Duckw^eed. 



Plants growing in large submerged masses: bodies long-stipitate. 1. L. trisulca. 



Plants floating, more or less detached; bodies sessile. 2. L. minor. 



1, L. trisulca L. Eoot-sheath acute: plant-bodies both submerged and aerial, 

 often falcate, 5-10 mm. long, acute: aerial plants smaller than the submerged 

 and short-stalked, cavernous; submerged plants with twisted stipes. — M. Eare, 

 in ponds. — Limestones. 



2. L. minor L. Eoot-sheath obtuse: plant-bodies elliptic, obovate, or sub- 

 orbicular, 2-4 mm. long, mostly 3-nerved, commonly keeled on the back and 

 papillose on the midrib : seeds 12-15-ribbed. — Susquehanna valley. Eather 

 rare, in ponds. 



2. SPIRODELA Schleid. Plant-body disk-like, conspicuously several- 

 nerved. Anther-sacs opening lengthwise. Utricle lenticular, with winged 

 margins. 



1. S. polyrhlza (L.) Schleid. Plants mostly sterile and perennial. Eoots 4-16: 

 plant-body obovate or suborbieular, 2.5-8 mm. long, 5-15-nerved: seeds smooth. 



— N. M. Eather common, in ponds and along streams. — Sandstones and 

 shales^ limestones. — Sum. 



