EQUISETACEAE (HORSETAIL FAMILY) 53 



.^antly shores, N. B. to Pa., Minn., and westw. May, June. (Eu) Possibly 



a liybrid. Figs. 14, 15. ^ 



14. E. litorale. Cross- 

 section of stem X 12. 



15. E. litorale. 

 Cross- section 

 of stem near 

 apex X 12. 



16. E. fluviatile. Cross- 

 section of stem X 12. 



6. E. fluviatile L. (Pipes.) Stems erect, 3-15 dm. high, with 10-30 shal- 

 low grooves, simple, or branched in the middle ; centrum | the total diameter; 

 vailecular holes absent except at bases of largest stems; branches 2.5-16 cm. 

 long, 4-6-angled, hollow, not winged, horizontal, with erect tips ; sheaths ap- 

 presse d ; teeth dark brown, narrow, acute, rigid, distinct. {E. limosum L.) 

 — Shallow water and mud-banks, common. June, July. (Eu.) Figs. 16, 17. 



§ 2. HIPPOCITAETE Milde. Stems mostly evergreen, simple or becoming 

 sparingly branched, mostly rough; spikes apiculate ; stomata (in onrs) 

 in a single regular row on each side of the groove, overlaid by the 

 siliceous coat of the stem, having access to the air through an irregular 

 hole. 



18. E. laevigatum. Cross- 

 section of stem X 12. 



7. E. laevigatum A. Br. Stems mostly annual, diffuse and rough or erect 

 and nearly smooth, 1-12 dm. long, simple or with few to many rough branches ; 

 centrum | the diameter of stem ; sheaths widened up- 

 ward, green with narrow black limb ; teeth of the stem- 

 sheaths mostly deciduous, leaving black triangular bases, 

 those of the branches persistent ; leaves flat above, ridged 

 below ; green parenchyma continuous under the keels, 

 separated by the vailecular bast. — Alluvial soils, 0. to 

 •B. C. and Tex. June-Aug. Fig. 18. 



8. E. hyemale L. (Scouring Rush.) Stems erect, 

 mostly simple, 3 to 9 dm. high, the ridges slightly grooved 

 on the back with a row of tubercles on each side ; 

 sheaths longer than broad, tight, with two black rings 

 separated by an ashy one ; teeth mostly deciduous ; 

 centrum usually | the total diameter ; green paren- 

 chyma continuous over the vailecular hoh s, separated by the bast under the 

 ridges. — Eu. 



Var. intermedium A. A. Eaton. Stems evergreen, simple, erect, 3-12 dm. 

 high, smoothish or rough with cross-bands of silex ; sheaths widened upward, 

 the lower with basal and terminal black rings separated by an ashy band, all 

 Bimilarly marked the second year; green parenchyma continuous over the 

 vailecular holes, separated by the carinal bast. — Moist sandy soils. Ct., 

 X. Y., and Mich, to Tex. and - Cal. May-Aug. —Often confused with E. 

 laevigatum. Fig. 10. 



Var. affine (Engelm.) A. A. Eaton. Differs from the type only in having the 

 nd^es rounded instead of biangulate. — Can. to Mex. ; common in N. E., less 

 common than Xho, next further west. 



Var. robustum (A. Br.) A. A, Eaton. Mostly stout, 12-30 dm. high, 6-18 

 mm. thick; ridges rounded; sheaths nearly as iDroad as long; leaves with d, 

 central and two lateral ridges ; teeth mostly persistent. (E. robustum A. Br.) — 



