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 farrows 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. Each of the scales is im- 

 pressed with two or three vertical lines. 



This plant grows naturally in boggy shady 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 



