116 BRITISH FERNS. 



The section of the stem differs from that of E, hyemale, to 

 which it presents a general resemblance,_ in being smaller, 

 showing fewer ridges, and having the cavities placed rather 

 nearer the inner margin ; the central cavity is also _ pro- 

 portionally smaller. It has, consequently, on the exterior, a 

 series of ridges formed of twin projections representing the 

 double row of silicious particles which extends along each 

 ridge ; and a series of cavities rather nearer the inner than 

 the exterior surface of the ring. 



This plant has been found on the moist banks of the 

 mountain glens of Scotland and the north of Ireland. 



THE GREAT ROUGH HORSETAIL. 



This plant is the Equisetum hyemale of botanists. The 

 'stems are of a deep glaucous green, and all alike in structure, 

 those which bear fructification differing in no other particular 

 from those which do not. They grow upright, from two to 

 three feet high, and are scarcely ever branched_: when this 

 does occur a solitary branch is produced, and this protrudes 

 from below the base of one of the sheaths of the stem ; they 

 are cylindrical, tapering off at the apex, and marked on the 

 thicker parts with from fourteen to twenty ridges, formed of a 

 double row of elevated points, consisting of crystallized sili- 

 cious particles ; hence the stems are very rough. In this 

 species the sheaths fit closely around the stems, so that they 

 are nearly cylindrical ; they are marked by the same number 

 of ridges as the stem, but they are less prominent, and ter- 

 minate in a series of black, membranous, bristle-shaped 

 teeth, which soon fall off, and leave the margin crenated. 

 The sheaths are at first pale green with a black margin ; 

 from this they change to be entirely black ; and finally they 

 become whitish in the middle, leaving a narrow ring of black 

 at the base and margin. 



In this species a section of the stem shows on the exterior 

 a scries of distinct ridges, formed of twin projections, and 

 varying in number, as has been already explained ; opposite 

 to the furrows, between them, and occupying about the centre 

 of the solid cylinder, is a ring of moderate-sized cavities. 

 The central cavity is comparatively large. 



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 steins of this Equisetum are employed in the arts as a 

 material for polishing, and are imported under the names of 



