ISOETACE^S. 147 



9' 20' or more long, with abundant stomata ; sporangia ob- 

 long linear-oblong, unspotted, with a narrow velum ; ligula 

 elongate from a triangular base; macrospores 0.40 0.52 mm. 

 thick, delicately honeycomb-reticulated; microspores usually 

 smooth, 0.024 0.028 mm. long. Var. Georgiana Engelm. has 

 fewer leaves and larger (0.48 0.56 mm. thick) macrospores. 

 New England and New York, Missouri and Illinois ; the vari- 

 ety in Horseleg Creek, Floyd County, Georgia (Canby). 



Var. gracilis Engelm. Leaves 8 12, often submerged, 

 9' 12' long, the bast bundles often quite small or only two 

 present. New England ; Passaic River, New Jersey (Ennis). 



Var. valida Engelm. Leaves 50 200, keeled on the upper 

 side, 18' 25' long; sporangia often linear-oblong 4" 9" long, 

 % to f covered by the broad velum ; macrospores 0.32 0.48 mm. 

 thick ; microspores spinulose, 0.0240.027 mm. long. Warrior's 

 Mark and Smithville, Pennsylvania (Porter); Wilmington, 

 Delaware (Canby). 



14. I. Howellii Engelm. Leaves 630 or even 50, 2' 8' 

 long, with numerous stomata and four bast bundles ; velum 

 variable, usually narrow in outer leaves, narrowly oblong on 

 inner leaves, usually densely spotted, and shining dark brown 

 or black ; sheath fuscous brown, deeply grooved ; ligula vary 

 from short triangular to 2" long; macrospores 0.48 mm. in diam- 

 eter, covered rather sparingly with low blunt isolated or conflu- 

 ent crests; microspores 0.02 0.03 mm. in diameter, light-brown, 

 covered with low blunt tubercles or spines. (/. nuda Engelm., 

 /. Undrii.<oodti Henderson.) Dalles of the Columbia, Oregon 

 (H owe II) to western Idaho (Henderson). 



ft Velum complete. 



15. I. flaccida Shuttleworth. Leaves 10 35, light-green, 

 15' 2 long, submerged, floating on the surface or wholly 

 emerged ; sporangia oval, 2" 3" long, entirely covered by the 

 velum ; macrospores 0.30 0.42 mm. thick, covered with many 

 or rarely few, large flattish tubercles, distinct or confluent into 

 labyrinth if orm wrinkles. Var. rigida Engelm. is smaller, with 

 more slender, erect, dark-green leaves, 5' 6' long. Lake Im- 

 monia, near Tallahassee, Florida (Rugel); also near Manatee, 

 Florida (Garber). The variety at Lake Flirt, Florida (Garber). 



