290 Proceedings of the Ohio State Academy of Science. 



I. Onoclca sensi'bilis L. Sensitive Fern. 



Rhizome slender and rootinj:^; leaves 1-4 feet hi,u,ii, l)r()a(l, 

 deeply piimatifid ; easily injured by frost; sporophylls bipinnate, 

 persisting over winter, the pinnules unrolling at maturity, ^'oung 

 petioles red. In moist soil. General in Ohio. 



Class II. EouiSETEAE. Horsetails and Scouring-rushes. 



25 species. 



Sporophyte perennial. herl)aceous, with a rhizome, and with 

 jointed, mostly hollow, sim])le or branched aerial stems which 

 are either annual or perennial; vascular bundles in a circle; 

 leaves reduced to sheaths around the joints, the sheaths toothed ; 

 sporangia borne on small peltate sporophylls arranged in whorls 

 on a terminal cone ; eusporangiate ; spores with four narrow, 

 strap-like, hygroscopic a])pendages. Gametophyte a small green 

 thallus, usually unisexual ; spermatozoids multiciliate. 

 Order, Equisetales. 



Equisetaccne, Horsetail Family. 



20. Equisetum L. Horsetail. Scouring-rush. 



1. Aerial stems annual, mostly with numerous branches except in some 

 of the fertile stems: cones rounded not with a point: stomata 

 scattered in the grooves. 2. 



1. Aerial stems annual or evergreen, mostly unbranched, not tuberculate; 

 cones with or without a point : stomata in a single regular row 

 on each side of the groove, ridges with broad transverse or 

 diagonal wart-like i)rotuberances: sheaths funnel-shaped, constricted 

 at the base E. laevigatum. 



1. Aerial stems evergreen, sheaths nearly cylindric or appressed : cones 



with a rigid point, stomata in regular rows : simple or sparingly 

 branched, o. 



2. Aerial stems of two kinds, the succulent pale and brownish fertile 



ones sometimes appearing before the green sterile ones. 3. 

 2. Aerial stems, all alike with whorls of simple, usually short, 

 branches; sheaths nearly cylindric; central cavity four-fifths the 

 diameter E. fluviatilc. 



