672 HYDROPTERIDES. 



forking, and terminated by the short (4" -6") nodding spike; leaves about 

 6-rowed, linear-subulate, entire, spreading or recurved ; those of the spike 

 ovate, acuminate, with bristly margins. — Springy sandy places, East Florida 

 [Curtiss), and Alabama {Mohr). 



Order HYDROPTERIDES. 



MARSILIA, L. 



Plants with filiform creeping stems, a whorl of 4 wedge-shaped leaves at 

 the summit of a long erect petiole, and one or more globular sporangia 

 borne on a slender stalk at the base of the petioles, each divided into sev- 

 eral partitions, which contain the larger and smaller spores. 



S. uneinata, A. Braun. Stem long ; leaves smooth or hairy ; sporangia 

 oval, compressed, half as long as the peduncle. — Banks of the Mississippi 

 below Vicksburg. 



ISOETES, L. 



I. melanospora, Engelm. Small, mostly monoecious; leaves few (5- 

 10), distichous (2' -2% long) ; spore-cases covered by the thin edges of the 

 cavity (velum) ; larger spores blackish, very minutely warty, the smaller 

 ones dull, papillose. (Engelmann.) — In shallow depressions on the summit 

 Stone Mountain, Georgia (Engelmann, Sfc). 



I. Engelmanni, A. Braun, var. Georgiana, Engelm. Leaves 10' - 12' 

 long, rather slender, stomatose; spore-cases oval, with narrow velum ; larger 

 spores and smaller spores smooth. — Slow-flowing water in Horseleg Creek, 

 mountains of Georgia. 



I. Blltleri, Engelm. Dioecious; trunk nearly globose; leaves 8-12, 

 bright green, 3' -T long; spore-cases usually oblong, spotted, the velum very 

 narrow, or none ; ligule subulate, from a triangular base ; larger spores 

 warty, smaller spores dark brown, papillose. (Engelmann.) — Barrens of Ten- 

 nessee (Or. Gattinger), and westward. 



