172 EQUISETACEZ 
other similar substances, and, under the name of Dutch Rush, has been 
imported in large quantities from Holland for their use. 
2. Rough Horsetail, Shave-grass, Dutch Rush (£. hyemdle).— 
Stem erect, rough, strongly marked with lines, usually biennial or perennial ; 
sheaths short, pressed close to the stem; teeth falling off. This species has 
not, like the last, two distinct kinds of fronds, those which bear the catkins 
being, in all other respects, exactly like those which are barren. It has none 
of the whorled tail-like branches around the main stem, though now and 
then a single branch is produced from the base of one of its sheaths. Its 
roots are strong and black, and its creeping underground stem extends to a 
great distance, and is jointed and branched by the whorled fibrous roots. 
The main stem of the frond is usually erect, two or three feet high, hollow, 
tapering towards the summit, and marked with from eight to thirty-four 
ridges. These ridges render the stem so rough to the touch that they are 
like a file, and their crystals of flint display, under the microscope, the most 
exquisitely beautiful arrangement. They abound both in the inner and outer 
cuticle, and form a complete framework to the plant. By some chemical 
process, the silica may be wholly freed from the vegetable portion, and the 
entire form of the stem and branches of the Horsetails preserved in beautiful 
clear crystal ; and when the vegetable remains are washed after the process, 
they are found to be quite free from a single particle of flint. The sheaths 
of this species clasp the stem quite closely, and are marked, though less 
strongly, with the same number of ridges. Black membranous bristle-shaped 
teeth, equal also in number to the ridges, terminate the sheath, soon dis- 
appearing, and leaving its margin indented with roundish notches, though 
the teeth of the sheath just beneath the cone remain. The teeth, which 
are at first pale glaucous-green, become afterwards black; they are pale in 
the middle, and have a deep black ring both at the top and base of the 
sheath. 
The catkin of this plant is small, and of a dark colour, and usually ter- 
minates the deep green stem ; or, if placed at the side, is never at any great 
distance from its summit. The scales, which are from forty to fifty in 
number, are marked with two or three lines. 
This is not a common species, and is apparently very local in those coun- 
ties in which it occurs, while it is almost unknown in the midland and 
southern parts of England. It has been found in moist woods at Hawthorn- 
den, Durham; in the neighbourhood of Newcastle; in Cumberland and 
Westmoreland ; near Scarborough, in Yorkshire, and several other northern 
localities ; also in South Kent, and in several places in Ireland, Wales, and 
Scotland. It is common in many moist lands and woods in some continental 
countries, as in Germany and Switzerland. In Holland it grows in plenty, 
and attains great luxuriance on the numerous embankments and by the sides 
of canals; and the large quantity of the plant brought annually to the 
London market has led many botanists to think that its culture along our 
sandy coasts would be of value from a commercial point of view, and that at 
the same time it would form a firm soil at the margin of the waters. Mr. 
Francis, who observes that on such places it would grow rapidly and luxuri- 
antly, and would yield a considerable profit, adds: “The Dutch are well 
