30 ENGELMANN—THE GENUS ISOETES’ IN N. AMERICA. [387 
mostly oblong (2 to 4 or even 5 lines long), shotted/ with narrow velum, 
ligula triangular-sybulate; macrospores among the smallest in the genus, 
<0.25 to 0.40 in diam., with depressed tubercles often confluent into worm¬ 
like wrinkles, or almost smooth; microspores also smaller than usual, 
0.023 to 0.028 or rarely 0.030 mm. long, spinulose.— Durieu in Bullet. 1. c.; 
Gray Man. 1. c. 
Var. pallida.. A larger plant, leaf-bases pale, velum usually much 
broader, covering \ or £ of the sporangium; macrospores only 0.30 to 0.35 
mm. thick, 
An exclusively western species, in low prairies and fields overflowed 
with at least one inch of water in spring, or in shallow ponds which dry 
up in summer, in stiff clayey soil, in company with the ordinary vegeta¬ 
tion of such localities, e.g. Nasturtium sessiliflorum , Hypericum mutilum, 
Elatine , Penthorum , LucL-ivigia, Ammannia , Alisma, Juncus , etc., from 
northern and central lllinois, Ringwood, G. Vasey; Athens, Menard Co., 
E. Hall; to Clinton, Iowa, G. Vasey , the Indian Territory, in low places 
in the saline flats near Limestone Gap, G. D. Butler , and to the wet pine 
woods in Hempstead Co. and about Houston, Texas, where the variety 
■occurs, E. Hall. Maturing in June or beginning of July. — Mr. Hall was 
accidentally led to the discovery of this plant on his farm in 1853 by find¬ 
ing its trunks and spores in turning up the soil for brick-making; he has 
since made many interesting observations about it; he does not find it 
every year, thus in 1877 there was none at all In localities where before 
and since it abounded, though the season was wet; another time he found 
it copiously only in plow furrows in a meadow, and none elsewhere; in 
wet seasons, when the water is deeper than usual about the plants, the 
leaves become longer, more flaccid, and even decumbent, and the spores 
mature later or not at all. In ordinary seasons the leaves disappear 
entirely in July'and nothing but the trunks remain, and about them the 
numerous spores, both of whtah are eagerly sought after by mice and 
other animals. The spores germinate whenever sufficient rain falls in the 
later summer months, and perfect meadows of young plantlets can be 
observed in wet autumns. Sometimes the plants are seen as fresh in Sep¬ 
tember as in May, and already 4H0 6 inches high, and in 1865 they were 
so much favored by the season that a second crop was gathered in Novem¬ 
ber with perfectly mature spores; but it is scarcely probable that these 
could have been seedlings of the preceding summer, though Mr. Hall is 
inclined to think so. 
The polygamous character of this species has been alluded to on page 
363. I will here only add, that a number of monoecious specimens show a 
preponderance of one or the other sex, and that in a few I have found 
leaves, which bear male or female sporangia, irregularly mixed. 
The dissepiments of the leaves consist of 6 to 9 layers of cells, the lower 
median being the thickest. Besides the normally 4 peripheral bast-bundles 
we find here often several smaller accessory ones, which increase the rigi¬ 
dity of the leaves. In no species have I seen the macrospores so variable 
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