246 HISTORY OF BRITISH FERNS. 



beauty. From these data Dr. Brewster concludes that 

 the cr3^stalline portions of silex and other earths which 

 are found in veo;etable films are not foreio;n substances of 

 accidental occurrence, but are integral parts of the plant 

 itself, and probably perform some important function in 

 the processes of vegetable life." 



Beyond their employment in the arts, the Equisetums 

 are of little importance in an economical point of view. 

 They are useless as fodder, and exploded as physic, though 

 they have had some reputed astringent virtues. The 

 under- ground stems, however, contain in winter, when the 

 plants are inactive, a considerable quantity of starch, and 

 they may be occasionally eaten by animals. In the cells 

 of these underground stems, during the month of October, 

 the particles of starch may be seen in active motion, 

 passing up one side and down the other, as is observed in 

 the stems of Chara. Dr. Lindley mentions having often 

 noticed this phenomenon in the stems of the great Water 

 Horsetail. 



The Horsetails consist of the one genus Equisetiwi, of 

 which some nine or ten species are recognized as British. 



