26 FLORA OF PHILADELPHIA. 



Family 6. VALLISNERIACEAE Dumort. Tape-grass Family. 



Stem branched ; leaves whorled or opposite. 1. Philotria. 



Acaulescent; stolonif erous ; leaves grass-like, elongated. 2. ValUsneria. 



Stem stolonif erous ; leaves broad, rounded, cordate, petioled. 3. Limnobium. 



1. PHILQTRIA Raf. Water-weed. 



Leaf-blades oblong, elliptic or ovate-oblong. 1. P. Canadensis. 



Leaf-blades narrowly linear. 2. P. angustifolia. 



1. Philotria Canadensis (Michx.) Britton. M. p. 60. Slow streams and 



ponds. Summer. 



2. Philotria angustifolia Muhl. In shallow water. Summer. 



Bucks— Point Pleasant, Britton (P.). 



2. VALLISNERIA L. 



1. Vallisneria spiralis' L. Tape-grass. Eel-grass. M. p. 60. In slow 

 waters. Late summer. 



3. LIMNOBIUM L. C. Richard. 



1. Limnobium spongia (Bosc.) L. C. Richard. Frog's-hit. M. p. 61. Stag- 

 nant water. Summer. 

 Monmouth— Swimming River (C). 

 New Castle — Delaware City, Commons. 



Order 8, GRAMINALES. 



Leaves 2-ranked, sheaths without united margins. Fruit a caryopsis; culm 

 mostly hollow. Fam. 1. Gramineae. 



Leaves 3-ranked, sheaths with united margins. Pruit an achene; eulm 

 solid. Earn. 2. Gyperaceae. 



Family 1. GRAMINEAE Juss. Grass Family. 



A. Spikelets 1 or 2-flowered; when 2-flowered the upper fertile, lower stam- 



inate; rachilla articulated below the scales or the subtending invo- 

 lucre, and not extending beyond the flowers. 

 Spikelets not flattened laterally. 



Flowering scale and palet hyaline; none of the scales spiny. 



Spikelets monoecious; staminate and pistillate in the same 



panicle. I. Maydeae. 



Spikelets in pairs, perfect, or the pedicellate one staminate, 



empty, rudimentary, or wanting. II. Andropogoneae. 



Flowering scale and palet of the perfect flower coriaceous or ehar- 



taceous; spikelets involucrate in Nos. 12 and 13; scales 3 or 4. 



III. Paniceae. 

 Spikelets flattened laterally, 1-flowered; scales 2. IV. Oryzeae. 



B. Spikelets 1-many-flowered; rachilla generally articulated above the two 



lower scales (below them in Nos. 28, 35, and 43) and frequently ex- 

 tending beyond the flower in 1-flowered spikelets. 

 Culms herbaceous. 



Spikelets upon pedicels in panicles, spike-like panicles or racemes, 

 not in rows. 

 Spikelets with but one perfect flower, which is terminal except 

 in Nos. 31 and 32, 



