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 pratense, 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. arvense and E. sylvaticum, 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 



