272 
HISTORY OF BRITISH FERNS. 
placed rather nearer the inner margin ; the central cavity 
is also proportionally smaller. It has, consequently, on 
the exterior, a series of ridges formed of twin projections 
representing the double row of siliceous particles which 
extends along each ridge ; and a series of cavities rather 
nearer the inner than the exterior surface of the ring. 
The fructification consists ^ small black cone-like 
heads, of an oblong form, terminating in an apiculus. In 
our specimens they appear sessile in the upper sheath, but 
they are said to become elevated on a short pedicel. The 
scales in one of these cones number about thirty. 
Equisetum ramosum is found on the moist banks of the 
mountain glens of Scotland and the north of Ireland. It 
was first found in Ireland, and apparently by two botanists 
in company, Dr. Mackay and Mr. Whitla ; this was in 
1833. It has subsequently been met with in other parts 
of Ireland, as well as in Scotland. 
Equisetum hyemale, Linnwxis. 
The Great Rough Horsetail (Plate XX. fig. 1.) 
The underground stems of this plant are branched, and 
creep to a considerable extent ; they are black, and fur- 
nished with whorls of branched, black, fibrous roots. The 
