128 FERNS OP GREAT BRITAIN. 



more than an inch long, are placed each on a partial 

 stalk about twice its length, one or two, or sometimes 

 three, of these terminating the main stalk. They are 

 formed of a number of triangular, egg-shaped, leaf-like 

 bracts, or involucres. The capsules are placed in the 

 angle formed by the bract and the stem. Each is two- 

 valved, kidney-shaped, of a pale yellow colour, and 

 filled with sulphur-coloured powder, single particles of 

 which are too small to be seen by the naked eye. After 

 these dust-hke seeds have escaped, the bracts all turn 

 downwards, and thus greatly alter the appearance of 

 the spike. 



Though this is the largest of our native Lycopo- 

 diums, yet in some other lands, as in the humid regions 

 of the tropics, and in the United States of America, 

 other species form a very conspicuous part of the 

 herbage, not always creeping along the soil like large 

 mosses, but standing erect, like miniature trees. Even 

 these, however, are small in comparison with the club- 

 mosses of older ages ; for the geologist finds in the coal 

 strata large species of similar plants, the Lepidoden- 

 drons, the numerous kinds of which must have formed 

 an essential part of the vegetation of the forests of 

 remote epochs. They have, with the ferns and horse- 

 tails, contributed more than any other plants to furnish 

 those beds of coal which form so important a material of 

 our comfort, and which have supphed the immense 

 means for the diffusion of knowledge, science, and 

 manufacture, by means of the steam-ship, the steam- 

 engine, and the printing-press. 



Those ancient plants, the Lepidodendrons, have stems 



