3 2 ' ENGELMANN—THE GENUS ISOETES IN N. AMERICA. [389 
rangium oblong or oval, entirely covered by the velum; macrospores verx 
variable in size, between 0.25 and 0.50 mm. thick, densely covered with 
minute but prominent rounded warts, or, "rarely, almost smooth; micro¬ 
spores 0.025 to 0-028 mm. long, papillose, brown. — Engelm. in Am. Nat. 
8, p. 215; I. o'paca , 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. 
Hally No. 693; at Milwaukee, Oregon, J. Howell (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 trilobed, 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—Sauvaile FI. Cub., p. 203, name only. 
On the bottom of rivulets in the pine woods of Eastern Cuba, Ckas. 
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. 
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