EQUISETUM. 
207 
ridges, rough with prominent flinty particles ; its sheaths 
are small, and about twenty in number ; the branches in 
each whorl are the same in number, they spread widely, 
are simple and jointed, and 
beset with flinty points. 
The fertile stems are only 
about 6 inches high, and have 
numerous joints, furnished 
with large loose sheaths, which 
almost cover the stem, they 
are slightly ribbed and pale 
whitish -green ; the cone is 
oval, chestnut-coloured, first 
sessile, then stalked ; the cap- 
sules are white, and fewer than 
in the last species. 
The third kind of stem is 
branched like the barren one, 
but less luxuriantly, and bears a small cone ; it is inter- 
mediate in size between the two. 
A section of the stem exhibits a series of sharp ridges 
and angular furrows on the exterior surface, and three 
circles of stomata, those of the two outermost circles 
small and circular, and those of the central one large 
and kidney-shaped ; the central cavity is small. 
This is a rare plant, but Dr. Greville has found it in 
Lanarkshire, Forfarshire, and near Edinburgh ; others 
have it from near Belfast, and from several localities in 
Yorkshire, Westmoreland, and Northumberland. 
It is generally distributed through Europe and North 
America. 
