164 ABOUT HORSETAILS, [CHAP. 
known as the Eguisetacee, a term which is almost 
literally translated in the popular name Horsetail. 
They are leafless, many-jointed, hollow-stemmed 
plants, which spring from an underground rhizome. 
At the joints the stems are solid, and they fit together 
by asort of sheath at the upper end of each joint, 
into which the lower end of the next joint fits. Im- 
mediately below the sheath a whorl of branches is 
given off, each branch being sheathed and jointed 
like the stem. A remarkable feature of this tribe of 
plants is the great quantity of silica, or flint, with 
which their stems are coated. In some this is so 
great that, on the plants being reduced to ashes, it is 
found that half the weight consists of silica. They 
may be macerated in water until the whole of the 
vegetable substances have been washed out, but the 
flinty coating still retains its form. This silica is 
deposited in the form of little crystals which give a 
rasp-like character to the stems; in fact, at least one 
species, &. kyemale, is largely used as a fine file for 
polishing wood, ivory, and metal. Large quantities 
are cultivated on the banks of the canals in Holland, 
and imported into this country under the name of 
Dutch Rush and Shave-grass. Their-long, 
branching underground stems and inter- 
lacing roots tend to make the embank- 
ments more secure. 
The fructification consists of a terminal 
Pic. ars. cone, made up of stalked discs, which bear, 
on their under surface, a number of spore- 
cases, opening longitudinally. The spores are pro- 
vided with four club-tipped elaters, which have pecu- 
