ISOETACEsE. M5 



0.300.45 mm. thick, marked with minute low tubercles, rarely 

 confluent into wrinkles ; microspores deep-brown, 0.026 0.031 

 mm. long, spinulose, rarely smooth. (/. California Engelm.) 

 Western Colorado (Brandt-gee), Utah, California, to Washing- 

 ton. 



2. Amphibious, partially emerged; stomat a always present. 



* Peripheral bast-bundles absent. 



t Velum partial. 



6. I. saccharata Engelm. Trunk usually flat, depressed ; 

 leaves 10 20, awl-shaped, spreading, olive-green, 2' 3' long ; 

 sporangia oblong, spotted, with a narrow velum ; ligula trian- 

 gular; macrospores 0.40 0.47 mm. thick, covered with very 

 minute, distinct warts, which are sometimes a little confluent ; 

 microspores papillose, 0.024 O2 8 mm. long. Banks of 

 Wicomico river, below Salisbury, and of Nanticoke river, East- 

 ern Maryland (Canby). 



7. I. riparia Engelm. Leaves 15 30, slender, rather rigid, 

 deep-green, 4' 8' long, with numerous stomata ; sporangia 

 mostly oblong, distinctly brown-spotted, i or ^ covered by the 

 velum ; macrospores 0.45 0.65 mm. thick, marked with isolated 

 or anastomosing, jagged crests; microspores more or less tuber- 

 culate, 0.028 0.032 mm. long. Banks of Delaware River from 

 Burlington to Wilmington, Delaware ; Uxbridge, Massachusetts 

 (Robbins)\ Brattleborough, Vermont (Frost) ; Maine (Checkering) ; 

 Crow River, Hastings County, Ontario (Macouri). 



tt Velum complete. 



8. I. melanospora Engelm. Trunk flat, only slightly 

 bilobed ; leaves 5 10, distichous, slender, tapering, light-green, 

 2' 2V long; sporangia orbicular or almost obcordate, i" i" 

 long, entirely covered by the velum ; ligula short triangular, 

 obtuse ; macrospores 0.35 0.45 mm. long, roughened with 

 distinct or rarely somewhat confluent warts, dark-colored ; 

 microspores smoothish or slightly papillose, 0.0280.031 mm. 

 long. In shallow excavations in granite rock, Stone Mountain, 

 Georgia (Canby). 



** Peripheral bast-bundles present. 

 t Velum partial or entirely wanting. 



9. I. Engelmanni A. Br. Leaves 25 100, light-green, 

 10 



