212 
BRITISH FERNS. 
sheaths, the teeth of which are pale, wedge-shaped, and 
tipped with black. Both kinds of stems are sometimes 
branched, the branches nu- 
merous, jointed, ascending, 
and with four or five ribs. 
The cones are oblong, an inch 
in length, stalked, and with 
many white capsules. 
There is a variety called 
Polystachion, where each 
branch of the upper whorl 
bears a small cone. 
Another variety, called nu- 
dum, has weak stems, decum- 
bent in the lower part, and 
appears merely a starved 
plant of the Common Marsh Horsetail. 
A section of the stem of this species presents a thick 
cylinder, very small central hollow, nearly even exterior, 
and two circles of apertures, each from four to eight in 
number, the outer larger, the inner small. 
This plant is as common as the last in marshy ground 
all over Great Britain and other temperate regions. 
64. Rquisetum. Iiyemale* Linn. Rough Horsetail* 
or Dutch Rushes. 
Caudex black, branched, creeping. Stems simple, erect, 
rarely branched, all alike, very rough, glaucous. Cones small, 
dark, pointed. 
The Rough Horsetail has numerous ribs, generally 
thirty-two, on the stem. All the stems are simple, as a 
rule ; there are, indeed, exceptive ones, which are slightly 
