Braun and Engelmanii's North American Equiseta. 85 



which, before the development of branches, distinguish the fer- 

 tile stem from E. arvense. E. sylvalicnm as well as E. arvense 

 have tubers on the creeping rhizoma, which Prof. Braun could 

 not find in E. eburneum ; the other species have certainly none. 



4. E. pratense, Ehrh. — Sterile (and finally also the fertile) 

 stems with simple straight branches, both grooved ; carinas sca- 

 brous, in one row; sheaths consisting of about 11 leaves, with 

 very shallow carinal and deeper commissural furrows, teeth sca- 

 rious, ovate-lanceolate, and all free ; carinas of the branches slight- 

 ly scabrous, much compressed ; urceolate sheaths consisting of 

 three 1-carinate leaves with herbaceous erect very short and 

 somewhat obtuse teeth. — E. umbrosum, Meyer, in Willd. E. 

 Ehrharti, Meyer, Chi. Hanov. E. amphibolum, Retz. E. tri- 

 quetrum, Bory. E. Drummondii, Hook. 



Hab. This species appears to inhabit extensively the northern 

 countries of Europe and Asia; it is rare in Scotland, common in 

 Scandinavia, in the North of Germany, in Russia and Siberia; 

 also in the Alps and Pyrenees ; in Arctic America and Greenland 

 according to Sprengel. It is easily distinguished from the forego- 

 ing, much more common, species by the shorter, never connate 

 teeth of the sheaths of the stem, the 3-teethed sheaths of the 

 branches, and the absence of branchlets. 



** Homophyaclica, {Summer Equiseta) : fertile and sterile stems similar, 

 both herbaceous and contemporaneous; or all the stems fertile. (All the 

 known species belonging to this section have annual stems, not persistent in 

 winter.) 



5. E. palustre, Linn. — Stems generally with simple verticil- 

 late branches, deeply grooved, somewhat scabrous; vallecular air 

 cavities large, the carinal ones very small ; sheaths loose, consist- 

 ing of about 8 leaves separated by shallow commissural furrows 

 and above with carinal ones; teeth lanceolate, acute, dark ferru- 

 ginous, with broad membranaceous margins ; branches smilar to 

 the stem, with acuminate adpressed somewhat sphacelate teeth 

 of the mostly 5-leaved sheaths. E. pratense, Reichenb., not 

 Ehrh. nor Roth. 



§. simplicissimum. Stems without branches. 



/. polystachyum. Branches elongated, bearing heads. 



Hab. Europe, North America, Arctic America to Virginia, 

 {Beck's Botany.) — Sheaths of the stem with 6 to 10, mostly 7 

 to 9 teeth. A very polymorphous species. Nearly related to this 



