HYDROCHARITACEAE. 31 



regular, of 3 or 6 segments, these united and tubular at base; 

 stamens 3-12; stigmas 3 or 6, bifid; ovary inferior; fruit inde- 

 hiscent. 



46. ELODEA. 



Perennials with opposite or whorled 1-nerved leaves; flowers 

 polygamo-dioecious, solitary and sessile in the axils; spathe 

 tubular, 2-cleft; perianth of the staminate flowers with 3 nearly 

 separate sepals and 3 or more narrower petals; perianth of the 

 pistillate flowers with a long scarious tube adherent to the ovary 

 and a 6-parted limb; stamens 3-9, the short filaments united at 

 base; stigmas 3-6, bifid. 



Elodea canadensis Michx. (Anacharis canadensis Planch.) Waterweed . 

 Stems 10-100 cm. long; leaves in whorls of 3 or 4, oval or oblong, acute, 

 usually serrulate. 



In ponds, not common in our limits. 



Family 16. POACEAE. GRASS FAMILY. 



Annual or perennial herbs, rarely shrubs or trees; stems (culms) 

 generally hollow ; nodes closed; leaves 2-ranked, sheathing, the 

 sheaths usually split to the base on the side opposite the blade; 

 a scarious or membranous appendage (ligule) borne at the 

 opening of the sheath, rarely obsolete; inflorescence a spike, a 

 raceme or a panicle, consisting of spikelets composed of two to 

 many 2-ranked imbricated bracts; the lowest two (glumes) 

 without flowers or rarely wanting; one or more of the upper 

 (lemma) containing in its axil a flower, which is usually enclosed 

 by a bract-like, generally 2-keeled, awnless organ (palea) oppo- 

 site the lemma and with its back toward the axis (rachilla) of the 

 spikelet; lemma sometimes bearing a hard thickening (callus) 

 at the base; flowers perfect or sometimes monoecious or dioecious, 

 subtended by 13 minute hyaline scales (lodicules) ; stamens 

 1-6, usually 3; ovary 1-celled, 1-ovuled; styles 1-3, commonly 

 2 and lateral; stigmas hairy or plumose; fruit a seed-like grain 

 (caryopsis) or rarely a utricle; endosperm starchy. 



Spikelets with two or more perfect flowers. 



Spikelets sessile on the rachis; inflorescence a 



spike. Tribe 8. HORDEAE. 



Spikelets pedicelled ; inflorescence a panicle, spike- 



klike panicle or raceme. 

 Lemma shorter than the glumes, usually with 

 a bent awn rising from the back. Tribe 5. AVENEAE. 



Lemma longer than the glumes, awnless or 

 with a straight apical awn. Tribe 6. FESTUCEAE. 



