Equisetum. EQUISETACE^. 481 



Rhizoma creeping extensively. Sterile stems 10-15 inches high, attenuated upward, 

 with numerous slender whorled branches, which are either simple or somewhat divided, bright 

 green : all the joints sheathed. Stomata irregularly disposed over the surface of the grooves, 

 between the ridges. Fertile stems appearing before the sterile ones, easily breaking at the 

 joints : sheaths dark brownish or purple. Heads or spikes oblong, obtuse ; the scales at first 

 closely approximated and of an elongated hexahedral form, more open when mature. Spores 

 (as in the rest of the species) singularly hygrometric, the filaments instantly coiling up if 

 breathed upon when they are dry. 



Moist banks and low grounds : frequent. Fr. April. Our plant is altogether like the Eu- 

 ropean JB. arvense. Towards the passes of the Rocky mountains, this species is abundant, 

 and constitutes a favorite and nutritious article of food for horses. 



•• Fertile stems at Ungik branched, bearing ike fructification at the same time with the branches. 



2. Equisetum sylvaticum, Linn, Wood Horsetail. 



Sterile and fertile stems both branched, about 1 2-furrowed ; the branches compound, and 

 curved downward ; sheaths loose, deeply cleft into several broadly lanceolate teeth. — Linn, 

 sp. 2. p. 1061 ; Pursh, fl. 2. p. 651 ; Bigel. fl. Bost. p. 384; Torr. compend. p. 390; 

 Beck, hot. p. 446 ; Darlingt. fl. Cest. p. 574 ; Braun ^ Engl. I. c. p. 84. 



Fertile stems 8 -12 inches high; the sterile ones taller: branches slender, chiefly from 

 the uppermost joints in the fertile stems ; all of them gracefully recurved. Stomata irregu- 

 larly disposed in the epidermis of the grooves. Sterile plants of an elongated conical form. 

 Spikes oblong. 



Low grounds and moist woods : not common. Fl. May. Our plant is exactly like my 

 European specimens. 



3. EauisETUM LiMosuM, Linn. Smooth Swamp Horsetail. Pipes. 



Stem smooth, with from 16-21 striae (sometimes simple) ; the branches nearly erect, 

 simple; teeth of the sheaths subulate, rigid, distinct, short. — Linn. sp. 2. p. 1062; Engl, 

 hot. t. 929 ; Torr. compend. p. 390 ; Bech, hot. p. 446 ; Braun <^ Engl. l. c. p. 86. E. 

 uliginosum, Muhl. cat. p. 103? ; Bigel. fl. Bost. p. 383 ; Pursh, fl. 2. p. 651. 



Stems 2-3 feet high, erect ; the branches usually simple and short, mostly arising from 

 the middle joints, sometimes very short or wanting. Stomata scattered over the intervals of 

 the striae. Sheaths appressed, numerous, with 15-20 acute narrow teeth, which are blackish 

 or bordered with dark brown. Spike oblong, about three-fourths of an inch in length. 



Borders of ponds and rivers, usually growing in the water ; sometimes in great quantities. 

 Fl. June. A common European species. 



[Flora — Vol. 2.] 61 



