STANDLEY — FLORA OF GLACIER PARK. 269 



Cones with a rigid point; aerial stems evergreen. 

 Sheath segments and deciduous teeth well differentiated; stems usually tall and 

 rigid, usually many-grooved; central cavity of the interuodes large. 

 Ridges of the stem with one row of tubercles; sheath segments without a central 

 groove or sometimes with a minute groove, normally tricarinate. 



1. E. praealtum. 

 Ridges of the stem with two rows of tubercles; sheath segments with a deep 



central groove, normally quadricarinate 2. E. hyemale. 



Sheath segments and teeth not sharply differentiated, the base of the teeth usually 

 persistent, but the bristle tip deciduous; stems low and slender, tufted, usually 

 with 10 or fewer grooves, the central cavity only one-half to one-third the 



diameter of the internode 3. E. variegatum. 



Cones rounded at the top or merely acute, not with a rigid point; aerial stems annual. 



not surviving the winter. 



Aerial stems all green and essentially alike. 



Fertile stems usually not branched, or the branches minute at time of maturing 



of the spores, very smooth, with cross bands of silex; sheaths elongate and 



dilated above, green, with a narrow black band at the top; plants of dry or 



ordinary wet soil 4- E. kansanum. 



Fertile stems branched, usually witli numerous whorls of bran ekes; plants of 

 wet soil, or growing in water. 

 Sheaths usually appressed; stems 45 to 90 cm. high, usually many -grooved, 



with a large central cavity in the internode 5. E. fluviatile. 



Sheaths loose and somewhat dilated; stems 15 to 45 cm. high, slender, 5 to 

 15-grooved. 

 Central cavity of the internode very small; cones well developed. 



6. E. palustre. 

 Central cavity about half the diameter of the internode; cones hnperfectly 



developed 7- E. litorale. 



Aerial stems of two kinds, the sterile shoots green and much branched, the fertile 

 ones brown and, at least at first, with little or no chlorophyll. 

 Fertile shoots withering after the shedding of the spores, very rarely producing 



branches 8. E. arvense. 



Fertile shoots producing compound branches after maturity of the spores, only 

 the tips withering 9- E. sylvaticum. 



1. Equisetum praealtum Raf. Occasional at low altitudes, in -^rillow thickets or 

 on rocky lake shores. B. C. to Calif., La., and Ohio.— Stems stout, 50 to 90 cm. high, 

 with a large central cavity, very rough; sheaths ashy or black in age, usually with a 

 black ring around the limb and a second one at the base, not dilated except when 

 young; cones large and thick. 



2. Equisetum hyemale L. Common at low altitudes, in swamps or wet thickets; 

 sometimes on open, well-drained banks. Widely distributed in N. Amer., Eur., 

 and Asia.— Stems stout, 0.5 to 1 meter high, very rough, with a large central cavity; 

 sheaths close, ashy or black, usually black-banded. 



3. Equisetum variegatum Schleich. Common, especially at middle altitudes and 

 above timber line; about pools, on lake shores, along streams, and in wet meadows 

 or thickets, often in sand or gravel. Alaska to Colo., N. Y., and Lab.; also in Eur. 

 and Asia.— Stems slender, 10 to 30 cm. high, 2 to 4 mm. thick, tufted; sheaths loose, 

 the teeth black, with a broad white border. 



This species is particularly abundant in meadows above or near timber line, and 

 often forms dense, almost pure stands of decumbent or ascending stems. Frequently 

 it grows up to the very edges of the snow banks. Occasionally it is found in culti- 

 vated ground at low altitudes. 



