ENGELMANN THE GENUS ISOETES IN N. AMERICA. 389 



rangium ofelong or oval, entirely covered by the velum ; macrospores very 

 variable in size, betw^een 0.25 and 0.50 mm. thick, densely covered with 

 minute but prominent rounded warts, or, rarely, almost smooth; micro- 

 spores 0.025 to 0.02S mm. long, papillose, brown. — Engelm. in Am. Nat. 

 8, p. 215; /. opaca, Nutt. in Hb. Ac. Phil. 



On damp prairie flats or springy declivities in the valley of the Colum- 

 bia river, Nuttall: abundant about Silverton in the Wallamette valley, E. 

 Hall, No. 693; at Milwaukee, Oregon, J. Hozvell (with almost smooth 

 macrospores); Klickitat Co., Washington Terr., on Kamass Prairie and 

 at the base of Mt. Adams, 2,100 feet alt., W. N. Suksdorf; eastward on 

 Kamass Prairie of the Coeur d'Aleines in Western Idaho, Ch. A. Geyer. — 

 The closed velum and the much smaller warts of the macrospores distin- 

 guish this readily from the two other terrestrial speeies ; it is the only 

 species on which I observe constantly only 3 peripheral bast-bundles, one 

 on each of the three edges, the upper middle one being absent. The me- 

 dian dissepiment of the leaves consists of 8 or 9 and the transverse one of 

 6 to 7 layers of cells. 



II. Trunk trilObCd, bast-bundles and numerous stomata in the quadrangular leaves; 

 velum partial. 



15. I. CuBANA, Engelm. One of the larger species; leaves 30 to 40, 

 15 inches long, fresh green, with 6 bast-bundles ; sporangia oblong, un- 

 spotted; velum very narrow; macrospores 0.30 to 0.40 mm. thick, marked 

 with coarse round depressed, never confluent tubercles; microspores 0.024 

 to 0.027 mm. long, papillose, pale. — Sauvalle Fl. Cub., p. 203, name only. 

 On the bottom of rivulets in the pine woods of Eastern Cuba, CJias. 

 Wright, probably floating. — This is the only American species north of 

 the Equator with a trilobed trunk; it compares most closely with the East 

 Indian /. Coromandelina according to A. Braun's observation. The roots 

 form 3 distinct bundles from the 3 grooves; the bast-bundles are found at 

 the four intersections of the dissepiments with the outer walls and at the 

 two upper edges of the leaf. 



