22 FLORA. 



Sterns all alike ; spores mature in summer ; branches simple or none, 

 j,- ,, u Sheaths rather loose ; branches usually long ; stems bushy below, attenuate 

 upwards. 



Central cavity Very small ; spike long. 4. E. palustre* 



Central cavity about one-half the diameter of stem ; spike short. 



5. E. lit tor ale. 



Sheaths appressed ; branches usually short. 6. E. fluviatile. 



Stems perennial, evergreen ; spikes tipped with a rigid point ; stomata in regular rows. 

 Stems tall, usually many-grooved. 



Stems rough and tuberculate, prominently ridged. 



Ridges with i line of tubercles ; ridges of sheath tricarinate ; stem stout. 



7. E. robustum. 

 Ridges of the stem with 2 indistinct lines of tubercles ; ridges of sheath 



obscurely 4-carinate ; stem slender. 8, E, hvemale. 



Stems not tuberculate ; sheaths enlarged upward. 9, , laevigatum. 



Stems low, slender, tufted, usually 5-io-grooved. 



Central cavity small ; sheaths 5-io-toothed. 10. E. variegatum 



Central cavity none ; sheaths 3-toothed. n. E, scirpoides. 



1. Equisetum arvense L. FIELD HORSETAIL. (I. F. f. 77.) Stems annual, 

 with scattered stomata, the fertile appearing in early spring before the sterile. 

 Fertile stems 1-2.5 dm. n *gh> n t branched, soon withering, light brown, their 

 loose scarious sheaths mostly distant, whitish, ending in about 12 brown acuminate 

 teeth ; sterile stems green, rather slender, 5 cm. -6 dm. high, 6-i9-furrowed, with 

 numerous long mostly simple verticillate 4-angled or rarely 3-angled solid branches, 

 the sheaths of the branches 4-toothed, the stomata in 2 rows in the furrows ; 

 central cavity one-fifth to one -fourth the diameter of the stem. In sandy soil, 

 especially along roadsides and railways, Newf. and Greenland to Alaska, south to 

 Va. and Cal. Also in Europe and Asia. An occasional form in which the sterile 

 stem bears a terminal spike is known as var. serotinum. 



2. Equisetum pratense Ehrh. (I. F. f. 78.) Stems annual, 2-4 dm. high, 

 with scattered stomata, the fertile appearing in spring before the sterile, branched 

 when old, only its apex withering, the two becoming similar ; stems rough, 8-20 

 ridged with narrow furrows and cylindric or cup-shaped sheaths ; branches straight, 

 rather short, simple, densely whorled, 3-angled or rarely 4-5 -angled, solid ; 

 sheaths of the stem with about II short ovate-lanceolate teeth, those of the branches 

 3-toothed ; rootstocks solid, acutely angled. In sandy places, N. S. and Rupert 

 R. to Minn., and Alaska, south to N. J. and Colo. Also in Europe and Asia. 



3. Equisetum sylvaticum.L. (I. F. f. 79.) Stems annual, with scattered 

 stomata, the fertile appearing in early spring before the sterile, at first simple, at 

 length much branched and resembling the sterile, only its naked apex withering. 

 Stems 2-5 dm. high, usually 12-furrowed, producing verticillate compound 

 branches, the branchlets curved downward ; sheaths loose, cylindric or cam- 

 panulate, those of the stem with 8-14 bluntish teeth, those of the branches with 4 

 or 5 teeth, those of the branchlets with 3 divergent teeth ; central cavity nearly 

 one-half the diameter of the stem ; branches and branchlets solid. In moist sandy 

 woods and thickets, Newf. and Greenland to Alaska, south to Va. and Mich. Also 

 in Europe and Asia. 



4. Equisetum palustre L. (I. F. f. 80.) Stems annual, slender, all alike, 

 2.5-4.5 dm. long, deeply 5-9-grooved, the grooves separated by narrow roughish wing- 

 like ridges, the central canal small ; sheaths rather loose, bearing about 8 subulate- 

 lanceolate whitish-margined teeth ; branches simple, few in the whorls, 4-7-angled, 

 always hollow, barely sulcate, more abundant below than above, their sheaths mostlv 

 5 -toothed ; spike rather long ; stomata abundant in the furrows. In wet places, 

 N. S. to Alaska, south to Me., W. N. Y., Minn, and Ariz. Also in Europe. 



5. Equisetum littorale Kuehl. (I. F. f. 81.) Stems annual^ very slender, all 

 alike, 24.5 ^m. n ^S n > slightly roughened, 6 ig-grooved, the ridges rounded, the cen- 

 tral canal one-half to two-thirds the diameter ; sheaths dilated above, the uppermost 

 inversely campanulate, their teeth herbaceous, membranous at the margins, narrow, 

 lanceolate ; branches of two kinds, simple, some 4-angled and hollow, some 3-angled 

 and solid, the first joint shorter or a trifle longer than the sheath of the stem ; spike 

 short with abortive-spores, these commonly with no elaters. On sandy river and 

 Jake shores, Me. and Ont. to N. J. and Penn., west to Br. Col. Also in Europe. 



