Ly { 
82 «Braun and Engelmann’'s.North American Equiseta. 
q .3 Equisera sPEIROPORA) ; in the second division they are disposed f 
regularly in‘two ranges on the sides of the grooves (E. sticuo- 
pora). ‘These ranges consist either, of one series or row of sto- 
mata each (as in all the northern species), or of two or more rows 
(as in many tropical ones). The stomata are only found in the 
grooves, never in the secondary furrows, even when these are of 
equal size and depth with the former. 5 ae 
ese The sheaths consist of united 1 verticillate leaves, free only on 
-* the points, which constitute the ¢eeth ; and these teeth correspond 
4° jn number and position with the ¢arine of the stem ; they are 
gee persistent or deciduous: e leaves have either a single 
*. 4 medial carina, or this carina is divided by a furrow, so as to ap- 
~ pear double; or sometimes the margins of the leaves are elevated 
and form two lateral carinee; thus the leaves may present from 
one to four carine. The furrow which sometimes divides the 
Prrincipat carina is the carinal furrow; "and another which is fre- 
“ quently found on the connecting line or the commissure “e° 
leaves is the commissural furrow. 
‘The section of the stem exhibits the following structure. In 
Ahe centre is a larger or smaller air-cavity or hollow space, lacuna, 
a7 (wanting only in FE. scirpoides); and around this a circle of 
‘\ generally-much smaller air-cavities whieh correspond with the 
grooves/or valleeule, and which we-thérefore call vallecular air 
C 
sfm. Exterior to these again is a cirele of alternating and still 
Fijuiseta there is no distivetion of fertile and sterile 
} ‘Homopnyapica. Some of these have annual — 
Stems, (E. xstrvauta, Siimmer-Equiseta,) such as EB’. palusire, 
aud E. limosum: others have perennial stems, not perishing in : 
> ~ winter, (E. nyemania, Winter-Equiseta,) suchas E. hyemale, 
OE E. scirpoides, etc. In asecond division, the fertile stems are dif- 
7 ferent from the sterile ones; the latter only being herbaceous, 
_ branching and persistent through the season, while the fertile are 
| ’ discolored and simple: such are E. neTeropuyapica. In some y 
ee @. these the fertile stems are deciduous after fructification (EB, vER- 
/ Lt _ NALA, Vernal Equiseta,) asin E. arvense and E. eburneum: 
, \ (- others, after fructification, produce verticillate herbaceous branch-_ 
” eee it 
bo a | 
