88 Braun and Engelmann's North American Equiseta. 



high ; but var. y. attains, according to the label in Prof. Short's her- 

 barium, a height of four feet and a half. The stems are simple, 

 or occasionally branched, with 20 to 24 carinas, but I have col- 

 lected specimens with from 18 to 27 carinae. Generally they are 

 perfectly smooth, but younger specimens and sometimes older 

 ones also are somewhat rough, with rather persistent teeth, ap- 

 proaching the small variety of the next species, but they can al- 

 ways be distinguished from that by the sheaths being nearly 

 twice as long, rarely with a black girdle at the base, more green, 

 and by the medial carinas of the leaves not extending to the point. 

 (In the small variety of E. robustum, it is strongly marked and 

 very rough.) The young sterile shoots with about 15 to 17 ca- 

 rinas are also more rough than the fertile stems, and resemble in 

 that respect the branches, which have 7 to 10 leaves with persist- 

 ent points. The sheaths, as has been stated, have generally only 

 a narrow black limb, but some specimens have also, especially 

 on the lower sheaths, a black girdle at base ; in one specimen I 

 have seen the whole sheath black. The spikes are generally 

 more obtuse than in E. hyemale. The var. y. has much the ap- 

 pearance of E. robustum, and it is equally large and stout, but is 

 very distinct in all other respects. From the very fragmentary 

 specimens seen by me, it seems impossible to distinguish it spe- 

 cifically from the Missouri plant. 



8. E. robustum, A. Braun. — Stems very tall and stout, erect, 

 simple or slightly branching above ; carinas narrow, rough with 

 one line of tubercles ; grooves shallow, on each side with a sin- 

 gle series of stomata ; vallecular air-cavities large, the carinal ones 

 nearly none ; central cavity very large ; sheaths short, adpressed, 

 with a black girdle above the base, rarely with a black limb, con- 

 sisting of about forty (in the branches eleven) leaves, 3-carinate 

 from the black girdle to the limb ; the points ovate-subulate, spha- 

 celate, deciduous, leaving an exactly truncate margin. E. proce- 

 rum, Bory ined., non Pollini. E.praialtum, Raf. ? 



§. minus, Engelm. Fertile stems with 28 to 31 carinas, 2 to 

 3 feet high ; points of the leaves more persistent. 



y. affine, Engelm. Fertile stems simple, with 20 to 25 ca- 

 rinas, 1 to 2 feet high ; teeth subulate-aristate, mostly persistent, 

 black, rough, finally becoming white. 



Hab. Islands of the Mississippi in Louisiana, (Bory de St. Vin- 

 cent.) Banks of Red River, (Dr. Hale, in herb. Short.) Banks 



