52 



EQ0ISBTACEAE (HORSETAIL FAMILY) 



I. EUEQUISilTUM Sadebeck. Stems annual, mostly with regular verticils 

 of branches; spikes not apiculate ; stomata^ in one or two broad bands in 

 each groove, their surfaces overlaid with a silex plate that bears a vertical 

 slit in the center. 



i/ 1. E. arvfinse L. 



T. E. arvense. Crose- 

 Bection of stem x 12. 



in threes ; centrum J 

 eter. — Alluvial soil, N. S. and Que. 

 to Alaska, southw. to w. Mass., N. J., 

 and la., chiefly in calcareous re- 

 gions. April, May. (Eurasia.) Figs. 

 8,9. 



3. E. sylviticum L. Stems 0. 7-4.5 

 dm. high ; both kinds developing com- 

 pound branches ; centrum half the 

 diameter ; ridges 8-14, flat, with a row 

 of recurved spinules on each side; 

 sheaths green, with the papery brown 

 teeth coherent ; primary branches 

 4-5-angled, the secondary 3-ang1ed. - 



(Common H.) Fertile stems 0.5-2.5 dm. high, with 

 loose 8-12-toothed sheaths, not rarely developing a few 

 branches in wet places ; sterile stems prostrate or erect, 

 0.6-5 dm. high, 10-14-furrowed, variously branched; 

 silex in punctiform dots; branches 3-4-angled, mostly 

 simple, solid, winged, the teeth of their sheaths triangu- 

 lar-lanceolate, with sharp erect acuminate points ; root- 

 stocks tuberiferous, felted ; centrum ^-| the total diameter 

 of the stem. — Common. (Widely distr.) Fig. 7. 



2. E. prat^nse Ehrh. Sterile and finally fertile 

 stems developing simple horizontal triangular branches 

 whose first in tern odes do not exceed the stem-sheaths; 

 teeth of branch-sheaths deltoid, acute; stems 2-3 dm. 

 high, 8-20- ridged,.beset with flat spines of silex, arranged 

 the total diam- 



. E. pratense. 

 Cross-section 

 of stem X 12. 



9. E. pratense. Epi- 

 dermis X 12. 



10. E, sylvaticum. 

 dermis x 12. 



Epi- 



E. sylvaticum. Cross- 

 section of stem X 12. 



Damp, shady places, Nfd. to Alaska, 

 southw. to Va., 0., and la.; com- 

 mon northw. May, June. (Eura- 

 sia.) Figs. 10, 11. 



4. E. paltistre L. Eootstocks 

 shining, black, solid at center; 

 stems 2.6-9 dm. high, deeply 5-10- 

 grooved ; ridges narrow, sharply 

 elevated ; sheaths widened up- 

 ward ; leaves centrally grooved ; 

 teeth lance-subalate, black, with 

 broad white margins; silex in 

 cross-bands ; centrum \ the total 

 diameter ; branches hollow, 4-7- 



angled. —Wet places, Nfd. to Alaska, southw. to Ct. (Graves), 111. (Brendel), 



etc. June-Aug. (Eurasia.) Figs. 



12, 1.3. 



5. E.litorJleKilhlewein. Stems 



diffuse to erect, simple to densely 



branched, 2-9 dm. high, 6-18- 



grooved ; centrum ^-f the total 



diameter ; vallecular holespresent ; 



sheaths slightly spreading ; teeth 



dark brown, acut,e, coherent in 



groups; branches 2.5-15 cm. long, 



3-5-angled, winged, often solid, 



similar to those of E. arvense; 12. E. pnlusu-e. Cross- 18. E. palustre. 

 usually abortive. — Wet, section of stem x 12. dermis x 12. 



Epi- 



