90 Braun and Engelmann's North American Equiseta. 



evidently 4-carinate leaves ; their points less deciduous, sphace- 

 late, nearly smooth. — E. paleaceum, Schleicher. 



y. trachyodon, A. Braun. — Stem smaller ; carinas more plain- 

 ly with two rows of tubercles, which are separated by a furrow ; 

 sheaths with a black limb, consisting of about ten evidently 4-ca- 

 rinate leaves, their points less deciduous, whitish or sphacelate, 

 rough on the back. 



Hab. Europe, with all the varieties ; in North America, only 

 the common form has yet been remarked : Pennsylvania, {Muh- 

 lenberg, Schweinitz,) Canada and Northern States, (Beck's Bot- 

 any, $*c.,) Michigan, (Engelmann,) to Kentucky, (Short.) Both 

 varieties will doubtless be found in this country. 



Specimens from the sandy shores of Manitou Island, Lake Mi- 

 chigan, have in the fertile stems 24 to 26 carinas, (in the smaller 

 sterile ones 17,) with nearly one row of tubercles; the black 

 limb of the sheath is somewhat indistinct ; leaves with 4 or some- 

 times (by obliteration of the carinal furrow) only 3 carinas; teeth 

 white, less deciduous, leaving a more exactly truncate margin. 

 Specimens from Kentucky have 20 to 28 carinas ; tubercles nearly 

 in one row ; leaves with 4 or only 3 carinas ; very near E. robus- 

 tum, y. affine ! Var. y. is by far the roughest form ; by its small- 

 er size, and plainly 2-rowed tubercles on the carinas, it approaches 

 to E. variegatum. E. hyemale is a northern plant, being re- 

 placed towards the south in North America, by the larger E. ro- 

 faistum, and in Europe by a smaller species, the much-confoun- 

 ded E. elongatum, Willd., (E. ramosum, Schleich., E. panno- 

 nicum, Kit., E. Illyricum, Hoppe, etc.,) which extends from 

 Southern Germany, through the whole of Southern Europe to 

 Northern Africa. Arabia, and middle Asia, and a variety of which 

 occurs again at the Cape of Good Hope, Isle of Bourbon, and Isle 

 of France : but it has not yet been met with in America. 



10? E. boreale, Bongard. — Found in Sitcha on the North- 

 west coast by Dr. Mertens, is unknown to me ; perhaps a variety 

 of E. hyemale? (A. Braun.) 



1 1. E. variegatum, Schleicher. — Casspitose ; stems low, simple ; 

 carinas rough with two rows of tubercles, separated by a furrow ; 

 the grooves larger and deeper than the furrows, on each side with 

 a single series of stomata ; vallecula!' air-cavities of the same width 

 as the central cavity, the carinal ones very small ; sheaths some- 

 what campanulate, variegated with black, consisting of about 



