274 
HISTORY OF BRITISH FERNS. 
exterior a series of distinct ridges, formed of twin pro¬ 
jections, and varying in number, as already explained ; 
opposite to the furrows between these, and occupying 
about the centre of the solid cylinder, is a ring of mode¬ 
rate-sized cavities. The central cavity is comparatively 
large. 
The cones of the fructification are rather small, and 
are seated on the apices of a number of the stems ; they 
are at first ovate and apiculate, subsequently becoming 
elliptical; when young, sessile in the sheath, but after¬ 
wards acquiring a short footstalk. They are dark-coloured, 
consisting of about forty to fifty scales, and abounding in 
light-coloured powdery spores. Bach of the scales is im¬ 
pressed with two or three vertical lines. 
This plant grows naturally in boggy sbady places, and 
is much more abundant northwards than southwards, where 
it is rarely met with. Though distributed sparingly over 
the , United Kingdom, its occurrence is strictly local. 
The stems of this Equisetum are employed in the arts 
as a material for polishing, and are imported under the 
names of Dutch Rush and Shave-grass. They are obtained 
from Holland, where this species is planted to support the 
embankments, which it does by means of its branching 
