EQUISETUM. 
251 
The central cavity is very large, the tissue of the stem being 
reduced to a very narrow ring. 
This is a widely-dispersed and rather common plant, oc- 
curring on moist banks and in muddy places, by the sides 
of streams and the margins of muddy pools. The nature 
of the soil would seem to be of small importance provided 
it has its necessary degree of moisture, for it is recorded as 
occurring both in sandy and in clayey soils, as well as in 
muddy pools. It is frequent in Ireland ; and is found 
both in Scotland and Wales. 
Equisetum pratenge, Ehrhart. 
The Shade Horsetail, 
This species of Horsetail was formerly named E, Drum- 
mondii^ after Mr. Drummond, who first discovered it as a 
native of Britain ; and has subsequently passed under the 
name E, umbrosum. It is a very interesting and distinct 
plant, intermediate in its general characteristics between 
E, arnense and E, syhaticum, but perfectly distinct from 
both. 
From its long, dark-coloured, creeping, underground stem 
are produced, at the joints, whorls of slender fibrous roots, 
and from buds organized at the same points arise the aerial 
