THE ORIGIN OF PLANT LII-^E ON THE LAND. 103 



kingdom, we may notice a little in detail some of its leading 

 forms. 



Beginning with the Mares'-tails, we find these represented in 

 the Carboniferous by many gigantic species, attaining to almost 

 tree-like dimensions (Fig. 96). These aie the Calamites, which 

 formed dense brakes and jungles on the margins of the great 

 swampy flats of this period. Their tall stems, ribbed and 



r*^ 





Fig. 95. — Astetophytliies pnrvula (Dn.), and Sf>henophyUnm antiquum (Dn), 

 Middle Devonian, New UruiiswicV. 



jointed, bore whorls of leaves or branchlets. Sending out 

 horizontal root-stocks and budding out from the base, they 

 grew in great clumps, and had the capacity to resist the effects 

 of accumulating sediment by constantly sending out new stems 

 at higher and higher levels. The larger species assumed a 

 complexity in the structure of their stems unknown in their 

 modern congeners, and enabling them to grow to a great 



