RO UGH HORSETAIL. 117 
high, of a glaucous green colour, throwing simple 
branches from the base, very rough to the touch on 
the surface. It grows freely in marshy districts in 
Great Britain, but is cultivated in great quantities on 
the canal banks of Holland, from whence it is imported 
under the name of Dutch Rushes. It is of areat 
value where it grows on account of the great length 
and interlaced growth of its root fibres, which mat 
together and consolidate the loose and swampy soil 
in which they grow, and thus form one of the most 
effectual water dams of the level land. An example 
of the development of the roots of Equisetum is 
afforded by the former species, E. palustre , which 
often fills up our drains and water pipes so com¬ 
pletely with its fibres, as to interfere with land 
drainage very considerably in some places. The 
amount of flinty matter contained in the stems of this 
plant is very remarkable. The particles are arranged 
most curiously and beautifully in two lines parallel to 
the axis of the stem, and may be distinctly seen 
under the microscope. Dr. Brewster observed the 
remarkable fact that each particle has a regular axis 
of double refraction. In the straw and chaff of barley, 
oats, and rye, he noticed analogous phenomena, but 
the particles were arranged in a different manner, and 
displayed figures of singular beauty. It is this species, 
under the name of Dutch Rushes, that is used ex¬ 
tensively as a polishing medium in the arts, either for 
bone, wood, or metal. 
