Braun and Engelmann's North American Equiseta. 87 



these ranges consist of a single row of stomata ; in many tropical 

 species each range has two or more rows. The spikes are mostly 

 acute. 



* Heterophyadica. (It is questionable whether any species exists belonging 

 to this section. E. mijriochaton, Sclilecht. and Cham, from Mexico, so far 

 known only from sterile specimens, might possibly prove to have different 

 and earlier fertile stems.) 



** Homophyadica. 



t Ranges of stdmata consisting each of one row. 



7. E. ljevigatum, A Braun. — Stems tall, erect, simple or some- 

 what branching ; carinas convex, obtuse, smooth ; grooves shal- 

 low on each side, with a single series of stomata ; vallecular air- 

 cavities small, the carinal ones very minute ; central cavity large ; 

 sheaths elongated, adpressed, with a black limb, consisting of 

 about twenty two leaves with one carina at base and (by the ele- 

 vation of the margins and depressions of the middle) two towards 

 the point ; points linear-subulate, sphacelate, caducous, leaving a 

 truncate-dentate margin to the sheath ; branches somewhat rough ; 

 sheaths with about eight indistinctly 3-carinate leaves ; points per- 

 sistent, subulate, sphacelate with a narrow membranaceous margin. 



§. scabreli.um, Engelm. — Carinas more elevated, somewhat 

 rough with small tubercles ; leaves above with two rather rough 

 lateral carinas, convex in the middle ; teeth subulate, black at the 

 base, membranaceous on the margin and towards the point, 

 mostly persistent. 



y. elatum, Engelm. — Very tall ; sheaths with about thirty 

 leaves, the points linear-lanceolate, membranaceous, irregularly 

 deciduous, leaving a ragged truncate-dentate black margin. 



Hab. On poor clayey soil, with Andropogon and other coarse 

 grasses, at the foot of the rocky Mississippi hills, on the banks of 

 the river, below St. Louis, (N. Riehl,) who discovered it 1840, 

 ( G. Engelmann) «. and (3. y. Near Newbern, North Carolina, 

 (Loomis fy Croom in herb. Short.) Mr. Curtis informs me that 

 this is probably the only species in that section. 



In size and manner of growth this new species is closely allied 

 to E. hyemale, and the larger variety to E. robustum ; but it is 

 easily distinguished by its smoothness, its long green sheaths, with 

 a narrow black limb, and its darker green color ; in some of these 

 respects it approaches to E. limosum, but differs by the deciduous 

 teeth, the regularly disposed stomata, the structure of the stem, 

 etc. It is generally one and a half to two, and even three feet 



