HISTORY OF BRITISH PERNS. 



cylinder of the stem occur two circles of cavities, the outer 

 one consisting of large openings, those of the inner minute, 

 and alternating with the larger. 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 UMBROSUM, Willdenow. The Shady Horsetail. 



This species of Horsetail was formerly named E. Drum- 

 mondii by Sir W. J. Hooker, after Mr. T. Drummond, who 

 first discovered it as a native of Britain, but it proves to be 

 the same which Willdenow had previously called E. urn- 

 brosum. It is a very interesting and distinct plant, inter- 

 mediate in its general characteristics between E. arvense and 

 E. sylvaticum, but perfectly distinct from both. 



Prom its long, dark-coloured, creeping, underground stem 

 are produced, at the joints, whorls of slender fibrous roots, 



