226 HISTORY OF BRITISH FERNS. 



quently opposite to the external ridges, occurs an annular 

 series of small circular cavities, which are placed near the 

 inner surface of the tube. 



This plant is not, as far as we are aware, applied to any 

 use ; and the harshness of its stems renders it by no means 

 agreeable to cattle, although it often occurs abundantly 

 among their pasturage ; and in cultivated ground becomes 

 a troublesome weed. 



EQUISETUM HYEMALE, Linnaus. The Great Bough 

 Horsetail. (Plate XX. fig. 1.) 



The underground stems of this species of Horsetail are 

 branched, and creeping to a considerable extent ; they are 

 black, and furnished with whorls of branched, black, fibrous 

 roots. The aerial stems are in this species all alike in 

 structure, those which bear fructification differing in no 

 other particular from those which do not. They grow up- 

 right, and are scarcely ever branched : when this does occur 

 a solitary branch is produced, and this protrudes from below 

 the base of one of the sheaths of the stem. Their colour is 

 a deep glaucous green. 



These stems, which grow from two to three feet high, are 

 cylindrical, tapering off at the apex, and marked on the 

 thicker parts with from fourteen to twenty ridges, formed 



