220 HISTORY OF BRITISH FERNS, 



Prom these data Dr. Brewster concludes that the crystalline 

 portions of silex and other earths which are found in vege- 

 table films are not foreign substances of accidental occur- 

 rence, but are integral parts of the plant itself, and probably 

 perform some important function in the processes of vege- 

 table life." 



Numerous stomates exist in the hollows of the fluted sur- 

 face of the stems, the depressed part of each channel having 

 two longitudinal series of these minute openings. 



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 underground 

 stems, however, contain in winter, when the plants are in- 

 active, a considerable quantity of starch, and they may be 

 occasionally eaten by animals. In the cells of these under- 

 ground 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 Cham. Dr. 

 Lindley mentions having often noticed this phenomenon in 

 the stems of the great Water Horsetail. 



The order of Horsetails consists of the one genus Equise- 

 tum, of which nine species are recognized as British. 



