ENGELMANN THE GENUS ISOETES IN N. AMERICA. 3S7 



mostly oblong (2 to 4 or even 5 lines long), spotted, with narrow velum, 

 ligula triangular-subulate; 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 J 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, Lud'^vigia^ Ammannia, AliaiJia^ jfuticus, etc., from 

 northern and central Illinois, 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 which 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 4 to 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 



