THE HORSETAILS. 103 



The Horsetails (Eguisetum). 



In the Horsetails we have the consideration not meiely of a 

 new genus of the Fern-allies, but a new Order and a new Class 

 the Equisetina. The Horsetails are a very distinct and remark- 

 able group of plants, in appearance utterly unlike the Ferns, and 

 yet there are certain points in their history in which some 

 resemblance to these plants may be traced. They are not an 

 extensive Order, only about five-and-twenty species being known, 

 and these are all members of a single genus. The characters 

 common to them all consist of a creeping underground root- 

 stock, in jointed lengths, from which more or less erect jointed 

 stems arise. These stems are tubular, except the two ends of 

 each joint, which are solid. The upper end of each length is 

 crowned by a sheath ending in long pointed teeth, into which 

 the lower end of the next joint fits. This leaf-sheath is com- 

 posed of a number of aborted leaves the only vestiges of leaves 

 these plants possess. Just below the leaf-sheath a whorl of 

 jointed branches is given off, each fashioned in a manner 

 similar to that of the upright stem. If the main stem is cut 

 across anywhere, except at the solid ends of the joints, it will 

 be found to be tubular. There is a central cavity whose 

 diameter varies with the species, and around this two or more 

 series of air canals, whose disposition is so distinct in each 

 species that a transverse section of the stem is an important 

 aid in their identification (Plate no). On its outer surface the 

 stem is coated with silica in such quantity that in some species 

 the whole of the vegetable matter may be got rid of by macera- 

 tion, yet the form of the stem will remain in a transparent flinty 

 skeleton. This exterior is thrown into a series of longitudinal 

 ridges and grooves, each species after its own pattern, and this 

 arrangement renders some of the species useful for polishing 

 metals, and gives them some slight commercial value. These 

 ridges on the stem correspond in number with the teeth of the 



