20 
ENGELMANN-—THE GENUS ISOETES IN N. AMERICA. [ 377 , 
§ 6. Enumeration of the Species. 
I. Trunk bilobed. 
A. Submerged, normally growing under water, only in unusually dry seasons 
coming above the surface; leaves quadrangular, without peripheral bast- : 
* Without stomata. 
1. I. lacustris, Lin. Leaves stout, rather rigid, obtusely quadrangu¬ 
lar, acute but scarcely tapering, dark or olive-green, io to 25 in number, 
2 to 6 inches long; sporangium orbicular to broadly elliptical, not spot¬ 
ted, with a rather narrow velum ; ligula triangular, short or somewhat 
elongated; macrospores 0.50 to 0.80 mm.* in diameter, marked all over 
with distinct or somewhat confluent crests ; microspores smooth, 0.035 to 
0.046 mm. in the longer diameter.— Syst. Veg. I. 1753; Durieu Bull. Bot. 
Soc. France, 8, p. 164, 1861; Gray Man. ed. 5, p. 675. 
Var. paupercula with fewer (10 to 18), thinner, shorter (2 to 3 inches) 
leaves and smaller spores '(macrospores-0^50 to 0.66 mm. diam.; micro¬ 
spores somewhat granulated, 0.026 to 0.036 mm. long). 
A northern species of Europe and America, generally gregarious on 
gravelly soil in the bottom of lakes under 1 to 4 or 5 feet of water, farther 
south only on mountains ; maturing in Sept, and Oct. Catskill Moun¬ 
tains, N. Y. Schweinitz, Echo Lake, Franconia Mountains, N. H. Tuck - 
ermann , Engelmann; in Massachusetts^ in Fresh Pond near Cambridge, 
W.Boott and Uxbridge, J-. W. Robbins ; Brattleborough, VtT* C.C. Frost; 
Saulte de Ste. Marie on Lake Superior, Porter and Leidy. The variety 
in Grand Lake, Middle Park, Colorado, over 8,000 ft. alt., Engelmann, 
and in Castte Lake near Mt. Shasta, California, 7,000 ft. alt., C. G. Prin¬ 
gle. — This is the original Linnean species, formerly confounded with 
others, and first clearly established by Durieu, 1 . c. It is always readily 
recognized by its rigid, rather thick, not gradually tapering dark green 
leaves, which do not collapse when taken out of the water, and by the size 
and sculpture of the spores. The variety paupercula is based on western 
mountain specimens, and is characterized by the smaller proportions of 
all parts, and especially of the (for the species) unusually small micro- 
spOres. Durieu, l.c. ii, p.'ioi, distinguished a form with exceptionally 
large macrospores (0.70 to 0.80 mm. diam.) as /. macrospora from a sin¬ 
gle specimen from the Herb. Acad. N. S. Philad., with the label “Catskill 
Mountains” in the handwriting of Schweinitz; but others show sometimes 
spores of similar dimensions, e.g. specimens from Lake Superior; and 
such have also been found in Europe, though there the spores rarely reach 
a size of over 0.65 to 0.70 mm. 
2. I. pygm^a, Engelm. One of the smallest species, with a few (5 to 
10) short (| to 1 inch long) stout, rigid, bright green leaves, abruptly 
* I adopt for the smaller measurements the metrical system, which will gradually but 
surely supersede the old and clumsy method, while in the larger measurements as the 
length of leaves, I still adhere to the foot and inch as the one yet best understood. The 
millimeter is, as is well known, equal to very nearly half a line. 
0 1 2 3 4 5 6 7 8 9 10 
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