The geographical distribution of this species and its 
forms has been discussed at length by G, H, Skull, [in 
Bot. Gaz. 36 : 187-202. ,1903.] 
tt Leaves 20 cm, or longei', 
2, I. valida (Engelm.) Clute. 
Isoetes Engelmanni valida Engelm, in Gray, 1. 
c. ed. 5. 677, ed. 6. 700. U?zderw, in 111. Fl. i : 
48; Nat Ferns 147; in Britt. 1. c. 29. 
/. valida Clute^ 1. c. 236. 
OUILLWORT. 
Plants with trunks sometimes 4 cm. thick; leaves 50 
to 200 in number, sometimes 6 dm. long; sporangia ob- 
long, 1-2 cm. 1. 
In pools and ditches. Summer. 
Near Great Falls, Potomac River, Ward-, Salt Pond Mt., Va., 
Cafiby, 
26. EQUISETUM Plinius. 
Equisaetum,^ hippurls Graecis dicta et in prat is 
vtttcperata nobis - est autem pilus terrae equinae simi- 
lis,^\\n. Hist. Nat. 26: ch. 132. 
Mostly robust plants. Rootstock creeping, mostly per- 
ennial. Stem erect, grooved, branchless in^soiiae. species, 
58 
