EQUISETACEAE (HORSETAIL FAMILY) 53 



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

 a hybrid. FIGS. 14, 15. 





14. E. litorale. Gross- 

 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 f the total diameter ; 

 vallecular 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- 

 pressed ; teeth dark brown, narrow, acute, rigid, distinct. (E. limosum L.) 

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



HIPPOCHAETE Milde. Stems mostly evergreen, simple or becoming 

 sparingly branched^ mostly rough; spikes apiculate ; stomata (in ours) 

 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. 



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 f 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 vallecular bast. Alluvial soils, O. 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 f the total diameter ; green paren- 

 chyma continuous over the vallecular holes, 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 

 similarly marked the second year ; green parenchyma continuous over the 

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

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

 laevigatum. FIG. 19. 



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

 ridges rounded instead of biangulate. Can. to Mex. ; common in N. E., less 

 common than the 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 broad as long ; leaves with a 

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



18. E. laevigatum. Cross- 

 section of stein x 12. 





