52 



EQUISETACEAE (HORSETAIL FAMILY) 



1. EUEQUISETUM 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. 



1. E. arvSnse L. 



7. E. arvense. Cross- 

 section of stem x 12. 



centrum 



in Tinrees , ^^nui^m. & DUO u\/u<n vnc*m- 

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

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

 and la., chiefly in calcareous re- 

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

 8, 9. 



3. E. sylvdticum 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 



(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, 

 0.5-5 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. prat6nse Ehrh. Sterile and finally fertile 

 stems developing simple horizontal triangular branches 

 whose first internodes 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- 



8. E. pratense. 

 Cross-section 

 of stem x 12. 



E. pratense. Epi- 

 dermis x 12. 



4-5-angled, the secondary 3-angled. Damp, shady places, Nfd. to Alaska, 



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

 mon northw. May, June. (Eura- 

 sia.) FIGS. 10, 11. 



4. E. palustre L. Rootstocks 

 shining, black, solid at center; 

 stems 2.5-9 dm. high, deeply 5-10- 

 grooved ; ridges narrow, sharply 

 elevated ; sheaths widened up- 

 ward ; leaves centrally grooved ; 

 teeth lance-subulate, black, with 

 broad white margins; silex in 



10. E. sylvaticum. Epi- 11. E. sylvaticum. Cross- Pr ncc.hiiTiH<a ppntriim 1 thp tntal 



dermisxl2. section of stem x 12. cross-Dands , centium g tne total 



diameter ; branches hollow, 4-7- 



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

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

 12, 13. 



5. E.litoraleKiihlewem. Stems 

 diffuse to erect, simple to densely 

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

 grooved ; centrum -|-f the total 

 diameter ; vallecular holes present ; 

 sheaths slightly spreading ; teeth 

 dark brown, acute, coherent in 

 groups ; branches 2.5-15 cm. long, 

 3-5-angled, winged, often solid, 



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

 spikes usually abortive. Wet, section of stem x 12. 



Epi- 



