90 FLORA OF PHILADELPHIA. 



Crhester (W. Tr.). Chester— {P.). Lancaster— (.P.). Lehigh — H-aIb- 

 burg, Jordan (Kr.). Northami)ton — (P.)- 

 New Jersey aud New Castle — Frequent. 



5. ACORUS L. 

 1. ACORUS Calamus L. Sweet Flag. Calamus. M. p. 231. Swamps and 

 along streams. Summer. 



Family 2. LEMNACEAE Dumort. Duckweed Family. 



Thallus with one root or several. 



Koots several. 1. Spirodela. 



Koot solitary. 2. Lemna. 



I'hallus rootless. 3. Wolffia. 



1. SPIEODELA Schleid. 



i. Spirodela POLYRHizA (L.) Schleid. M. p. 232. Ponds and pools. Summer. 



2. LEMNA L. Duck-weed. 

 Thalli long-stipitate. 1. L. trisulca. 



Thalli short-stipitate or sessile. 



Spathe open. 2. L. perpusilla. 



Spathe sac-like. 3. L. minor. 



1. Lemna trisulca L. M. p. 232. Ponds and springy places. Summer. 



Philadelphia— FranMord, Jesse BurJc (B. C). Bucks— In shallow 

 pond in Trap Rock Region (Fr.). Chester— {P.). Lancaster— {P.). 

 Northampton — (P.). 



2. Lemna perpusilla Torr. M. p. 232. Ponds and springs. Summer. 



Northa7npton— (P.) . 



New Castle— Ditches near Edgemoor, New Castle, Commons (now 

 extinct there). 



3. Lemna mikur L. M. p. 233. Stagnant water. Summer. 



3. WOLFFIA Horkel. 

 1. Wolffia Columbiana Karst. M. p. 234. Floating beneath the surface 

 of stagnant water. Summer. 

 Philadelphia— '^eck (Cr.). ^wcA-s— Tullytown (Cr.). 

 C«/ndeH — Kaighn's Point (C). 6'aZem— Jumbo Station (He.), W. of 

 Fedricktown (Li.). 



Neiv Casiie— Ditches and Canal Coves. 



Order 5. XYRIDALES- 



Ovary 1-celled. 



Erect-scapose rush-like herbs; flowers in terminal scaly heads or spikes. 



Fam. 1. Xyridaceae. 

 Mud or aquatic herbs, the flowers subtended by spathes (Heteranthera 

 in Pontederiaceae). 

 Ovary 2-3-celled. 



Flowers very small, densely capitate, monojcious or dioecious. 



Fam. 2. Eriocaulaceae. 

 Flowers perfect. 



Perianth of 2 series of parts, the outer (sepals) green, the inner 



(petals) colored. Fam. 3. Commelinaceae. 



Perianth 6-parted. Fam. 4. Pontederiaceae. 



