1 64 ABOUT HORSETAILS, [CHAP. 



known as the Equisetacece, 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 a sort 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, E. hyemale, 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 

 FIG. n6.' 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- 



