52 



EQUISETACEAE (HORSETAIL FAMILY) 



>^ 1. EUEQUISETUM Sadebeck. Stems annual, mostly with regular Mrticil^ 

 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. arvense L. 



7. E. arvense. Cross- 

 section of stem X 12. 



in threes ; centrum ^ 

 eter. — Alluvial soil, 

 to Alaska, south w. to 

 and la., chiefly in 



(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 |-f the total diameter 

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



2. E. pratense 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 diara- 

 N. S. and Que. 

 w. Mass., N. J., 

 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. - 



10. E. sylvaticum. 

 dermis x 12, 



E. sylvaticum. Cross 

 section of stem X 12. 



angled. —Wet places, Nfd. to Alaska 

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

 12, 13. 



5. E.litoraleKuhlewein. Stems 

 diffuse to erect, simple to densely 

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

 grooved ; centrum ^— | 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; 

 spikes usually abortive. — Wet, 



S. E. iiratense 

 Cross-section 

 of stem X 12. 



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 

 cross-bands ; centrum I the total 

 diameter ; branches hollow, 4-7- 



southw. to Ct. {Graves), 111. (Brcndel), 



12. E. palustre. Cro^s 

 section of stem x 12. 



13. E. palustre. Epi- 

 dermis X 12. 



