EQUISETUM. 
209 
teeth. The capsules are arranged round the cone in 
crowded whorls, accompanied by numerous scales; the 
spores are of a beautiful blue-green. 
A section of the stem exhibits a small central cavity, 
a merely undulating exterior owing to the bluntness of 
the ridges, and two circles of apertures, the outer large, 
the inner small. 
This is the commonest of our Horsetails, infesting the 
land to a great extent, and very difficult to eradicate. 
It prevails chiefly where the ground is sandy, and is 
very injurious to cattle, owing probably to the sharp 
flint particles so freely immersed in its substance. 
Its foreign habitat extends all over Europe and North 
America. 
61. Equisetum sylvaticum, Linn. Wood Horsetail. 
Caudex creeping, branched, dark-coloured. Loots slender. 
Barren and fertile fronds slightly different. Burrows 12. Cone 
blunt. 
The Wood Horsetail has a caudex which creeps widely. 
Both the stems appear at the same time, and put forth 
whorls of drooping branches. The barren stem is more 
slender than the fertile one, the branches more nume- 
rous and more fully furnished with secondary branches. 
The ribs are fully developed, the sheaths fit closely, and 
are cut into four or five broad teeth ; the whole height 
of the frond is from 15 to 18 inches. 
The fertile ones are later in putting forth their 
branches, but eventually they droop, and bear secondary 
branches like those of the barren frond. The stems are 
round, succulent, and pale ; flinty particles are imbedded 
in the ridges, but they are too small to cause any very 
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