2 



stems green, 8 — 20 inches high, much branched, 6—19 fur- 

 rowed ; branches 4— angled. Common in sandy soil all over the 

 state. Fruiting in March and April, 



** Stems all alike^ evergreen^ simple or with a few short 

 erect hranches. Fruiting in the summer. Sheaths appressed. 



E. HYEMALE L. (Scouring-rush.) Stems 1 — 4 feet high, 

 rough, 8— 34 grooved. Sheaths cylindric, enlongated, with a 

 dark band near the base and a black limb. Teeth blackish, 

 membranaceous, deciduous. Central air cavity of the stem large. 

 Common along streams or near springy places. July — Septem- 

 ber. 



E. LAEViGATUM Braun, Stems 1 — 4 feet high, slender, pale 

 green, 14 — 30 furrowed. .Sheaths enlarging slightly upwards, 

 with a black girdle nt the limb and rarely an obscure one at the 

 base. Teeth deL'iduous, white margined, June — July. In up- 

 land soil. Common in the western part of the state and fre- 

 quent generally. 



E ROBUSTUM Braun. Stems 3—11 feet high and sometimes 

 one inch thick, 20—48 furrowed. Sheaths short, cylindric, 

 marked with black girdles at the base and at the base of the de- 

 ciduous teeth. River banks. Reported by Arthur from Keokuk 

 and Clinton countie^i and by.Fiok from Fayette county. 



*** Stems annual^ f netting during the summer^ all of one 

 hind or the two kinds contemporary^ herbaceous. 



E. LiMOSUM L. Stems 2—3 feet high, slightly many fur- 

 rowed, usually producing many upright branches after fructifica- 

 tion. Sheaths appressed with 18 dark-brown short acute rigid 

 teeth. Shallow water. Reported by Arthur from Story- 

 county and by Cratty from Emmet county. 



Order 2. FILICES JUSS. 



AcotyledinouB plants, perennial in our species, terrestrial 

 stemless. Rootstalks creeping or descending. Fronds leaf like 

 usually stalked, from 1 — 3 pinnate or entire, growino^ from the 

 upper side of a creeping rhizome or in tufts or crowns termin- 

 ating erect stems. Sporangia in clusters, variously arranged on 

 the back or margin of the fronds. On reaching development 



