52 



EQUISETACEAE (HORSETAIL FAMILY) 



1. EUEQUISETUM Sadebeck. Stems annual, mostly icith 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. 



(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 punctifonn 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 

 ol the stem. Common. (Widely distr.) FIG. 7. 



2. E. pratSnse 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 fiat spines of silex, arranged 



the total diam- 



N. S. and Que. 



8. E. pratense. 

 Cross-section 

 of stem x 12. 



9. E. pratense. Epi- 

 dermis x 12. 



in threes ; centrum 



eter. Alluvial soil, 



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



and la., chiefly in calcareous re- 

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



8,9. 



3. E. sylvaticum 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-angled. Damp, shady places, Nfd. to Alaska, 



southw. to Va., 0., 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 ; 

 tee'li lance-subulate, 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. (Gnu-if. 111. ( Hi-nnli-l}, 



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



12, 13. 



5. E.litoraleKiililewem. 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. en..-*- 13. E. palustre. Epi- 



spikes usually abortive. Wet, section of stem x 12. dennis xl2. 



10. E. sylvaticum Epi- 

 derims x 12. 



11. E sylvaticum Cross- 

 section of stem X 12. 



