THE GENUS EQUISETUM WITH REFERENCE TO THE 

 NORTH AMERICAN 5PECIES. 



By Alvah A. Eaton, 



NINTH PAPER. 

 E. Litorale Kuhl. 



RHIZOME shining dark brown, with narrow central cavity at 

 times bearing a few tubercles. Stems prostrate or ascend- 

 ing, a few inches to three feet high, fertile and sterile alike, 

 finely roughened with cross-walls of silica, as in palustre, with 

 6-18 rounded angles and shallow grooves, naked or variously 

 branched, but always ending in a slender naked tip. Lower 

 sheaths appressed or becoming open when dry, longer than broad, 

 partly or wholly brown, the upper more often colored like the 

 stem, the uppermost, in fertile stems, bell-shaped. Leaves 

 rounded on the back, slightly angled below. Teeth narrow 

 lanceolate, often joined in twos or threes by the very narrow 

 white margins, dark brown, sharply pointed, on the largest 

 sheaths often acquiring a median groove in drying. Stomata 

 many, irregularly scattered in the grooves, as broad as long. 

 The central cavity occupies Y~Y the diameter of the stem, the 

 carinal present, surrounded with a ring of yellowish cells, the 

 vallecular usually present, only occasionally one being absent. 

 Branches when present dark green, the darkest of our Equiseta, 

 scattered or 10-15 in a dense verticil, simple or rarely branched, 

 confined to the lower internodes or oftener to the middle ones, 

 Y> in. long, 3-5 wing-angled, with fine cross bands of flint, as- 

 cending or erect, seldom arched as in fluviatile, lower internode 

 about equaling the stem sheath, solid or with small central 

 cavity, the inner portion bordered with yellowish cells. Fruit 

 spikes yellowish, raised on a fleshy peduncle, the sporophylls 

 not separating as in other species, apparently never perfecting 

 spores, sterile stems or even branches often ending in a small, 

 sessile abortive spikelet. 



A very polymorphous and puzzling species, presenting a 

 maze of forms not approximated by any other. At times it 

 grows in dense patches on the sandy river border, 2-3 feet high, 

 with few or no branches (gracile) ; again it is found in a wetter, 

 slightly muddy place with Jiuviatile and simulates that species 

 by becoming densely verticellate ' {elatius) ; now it grows in 

 rather loose wet sand and bears a large spike {humile), and now 



