ISOETACE^. 143 



microspores. Name from Gr. /cro?, equal, and ero?, year. Con- 

 tains about 50 species, of which sixteen are found within our 

 limits. 



Note.— The measurements of the spores are given in millimetres; mm. = .03937 

 inch. 



§ I . Submerged, rarely abcn'e water in driest seasons ; leaves 

 quadrangular without peripheral bast-btmdles ; velum incom- 

 plete. 



* Stomata absent. 



1. I. lacustris L. Leaves 10—25, stout, rather rigid, ob- 

 tusely quadrangular, acute but scarcely tapering, dark or olive- 

 green, 2 — 6' long; sporangia orbicular — broadly-elliptic, with a 

 narrow velum ; ligiila triangular, short or somewhat elongate ; 

 macrospores 0.50 — 0.80 mm. in diameter, marked all over with 

 distinct or somewhat confluent crests; microspores smooth, 

 0.035 — 0.046 mm. long. Var. pauper cula Engelm. has fewer, 

 thinner and sliorter leaves and smaller spores, the microspores 

 somewhat granulate, 0.026 — 0.036 mm. long. (/. macrospora 

 Durieu.) Catskill Mountains, New York {Schweinitz), Echo 

 Lake, New Hampshire {Tucker man). Fresh Pond, near Cam- 

 bridge, Massachusetts ( W. Boott), Uxbridge, Massachusetts 

 {Robbins), Brattleborough, Vermont (Frost), Lake Superior 

 (Porter). The variety from Grand Lake, Middle Park, Colo- 

 rado (Engelmann) and Castle Lake near Mt. Shasta, California 

 (Pr ingle) . 



2. I. pygmaea Engelm. Leaves 5 — 10, stout, rigid, bright- 

 green, y — i' long, abruptly tapering to a fine point, witii very 

 short often almost square epidermal cells; sporangia f)rbicular 

 with a narrow velum; macrospores 0.36 — 0.50 mm. thick, 

 marked with minute, rather regular, distinct or rarely confluent 

 warts; microspores brown, almost smooth, 0.024 — 0.029 mm. 

 long. Mono Pass, California {Bolande7-). 



3. 1. Tuckermani A. Br. Leaves 10 — 30, very slender, 

 tapering, olive-green, 2' — 3' long, tlie outer recurved ; sporangia 

 mostly oblong, white or rarely brown spotted, the upper third 

 covered by the velum; macrospores 0.44 — 0.56 mm. thick, the 

 upper segments marked with prominent, somewliat parallel and 

 branching ridges, the lower half reticulate ; microspores smooth 



