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1. ISOBTES L, (QuILLWwonrts. ) 
The only genus, possessing the characters of the order. 
1. I. melanopoda J. Gay. Polygamous: trunk subglobose, deeply bilobed : leaves 
15 to 60, slender, erect, bright green, 1 to 2.5 dm. long, usually black at base: 
sporangia mostly oblong, 4 to 10mm. long, spotted with a narrow velum: macrospores 
0.25 to 0.4 mm. thick, with depressed tubercles often confluent into worm-like 
wrinkles or almost smooth: microspores spinulose, 0.023 to 0,028 mm, thick,—Houston 
(Hall). The Texan specimens are of the var, PALLIDA Engelm., with paler bases 
to the leaves of the taller more robust plants. 
EQUISETACEA. (HoRSE-TAILS.) 
Plant body rush-like, with jointed and usually hollow stems, the sterile 
leaves reduced to sheaths at the joints, the fertile forming a short spike 
terminating the stem.—Plants of sandy banks and wet places. 
1. EQUISETUM UL. 
Perennial plants with wide creeping rootstocks: stems simple or 
branched, furrowed lengthwise, hollow: sporangia adhering to the 
under side of shield-shaped scales of the spike, one-celled, opening 
down the inner side: spores furnished with two slender filaments 
(elaters), which are attached by the middle and uncoil when dry. 
1. B. hiemale L. Stems 3 to 12 dm. high, rough, 8 to 34-furrowed; ridges with 
two indistinct lines of tubercles: sheaths rather long, eylindric, marked with one 
or two black girdles; ridges of the sheaths quadricarinate; teeth membranous, soon 
deciduons.—Houston (arene), 
It is not unlikely that the closely allied species EL. robustum will also be found 
within our limits. 
2. EB. levigatum A. Braun, Stems 8 to 12 dm. high, rather slender, 14 to 30- 
grooved, nearly smooth: sheaths somewhat enlarged upward, marked with a black 
ring at the base of teeth, which are white-margined and usually deciduous; ridges 
of the sheath uniearinate or obscurely tricarinate.—Banks, Hempstead, Waller 
County (Hall). 
SALVINIACEZ. 
Small floating plants, with a more or less elongate and branching 
axis bearing apparently distichous leaves: sporocarps thin-walled, two 
or more on a common stalk, one-eelled, with a central receptacle bear- 
ing macrosporangia containing a single macrospore, or microsporangia 
containing numerous microspores. 
1. AZOLLA Lam. 
Small moss-like plants with pinnately branching stems covered with 
minute imbricate bilobed leaves, and emitting copious rootlets beneath, 
1. A. Caroliniana Willd. Floating usually in matted tufts, greenish in shade, red- 
dish in the sunshine: plants 8 to 25 mm. broad: leaves with ovate lobes: macro- 
spores minutely granular: masses of microspores barbed at the tips, the stems of the 
barbs septate. 
Cypress swamps near Victoria (Lindheimer). 
