ISOETACEJE. 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 (Enm's). 



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; microsporesspinulose, 0.024— 0.027 ra™- long- Warrior's 

 Mark and Smithville, Pennsylvania (Porter'); Wilmington, 

 Delaware (Canby). 



14. I. Howellii Engelm. Leaves 6 — 30 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. (/. tiuda Engelm., 

 /. Underwoodii Henderson.) Dalles of the Columbia, Oregon 

 (Howell) to western Idaho (Henderson). 



tt Velum complete. 



15. l.flaccida Slmttleworth. 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 

 labyrinthiform 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), 



