PERNS OP GREAT BRITAIN. 129 



of the same essential structure as those of our Club- 

 mosses, are branched in the same way, and have similar 

 leaves and fructification. While, however, our Lycopo- 

 diums are so moss-like that the older botanists described 

 them as mosses, the fossil Lepidodendrons must have 

 attained the height of trees, and had thick bases to their 

 stems as large as the trunks of our oaks or firs. Leaves 

 some inches long grew on their stems and branches, and 

 under their shadow were developed those large ferns 

 and horsetails, which are so abundant in the coal- 

 measures, that ferns seem at one time to have formed 

 more than three-fifths of the earth's vegetation. Doubt- 

 less they aided by their living growth the purification of 

 the atmosphere, and how much we owe to their decom- 

 posed substance no pen can describe. If these gigantic 

 plants are not exactly identical with the modern Lycopo- 

 diacese, yet they are so nearly so, that Httle difference 

 can be discovered by those who have most patiently and 

 skilfully investigated the plants of the coal strata. 



Our native club-mosses have no very great beauty to 

 recommend them to our notice, save the green tint 

 which they give to the hiU-side or mountain-slope, or 

 dripping rock or waterfall. They are a peculiarly Alpine 

 tribe of plants, L. inunddtum being the only species 

 frequent in the low lands of the south-east of England. 

 The stems of aU are clothed with leaves densely crowded 

 upon them, like the tiles on a roof; an arrangement 

 which the botanist terms imbricated. The fructification 

 is placed in the axils of the leaves or bracts, that is, in the 

 angles between these and the Stems; and it generally 

 grows in a cone at the top of the stem. It consists of 



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