THE CARBONIFEROUS FLORA. 



125 



and complicated stems belonged to higher and nobler 

 types of mare's-tails than those of the modern world, and 

 that their fructification was equisetaceous and of the 

 form known as Calamostachys. 



We have already seen that noble tree-ferns existed in 

 the Erian period, and these were continued, and their 

 number and variety greatly extended, in the Carbonifer- 

 ous. In regard to the structure of their stems, and the 

 method of supporting these by aerial roots, the tree-ferns 

 of all ages have been nearly alike, and the form and 

 structure of the leaves, except in some comparatively rare 

 and exceptional types, has also been much the same. 

 Any ordinary observer examining a collection of coal- 

 formation ferns recognises at once their kinship to the 

 familiar brackens of our own time. Their fructification 

 is, unfortunately, rarely preserved, so that we are not 

 able, in the case of many species, to speak confidently of 



Fig. 50. — Stems of Calamodendron and tissues magnified (Nova Scotia), 

 a, b, Casts of axis in sandstone, with woody envelope (reduced). 

 <?, d, Woody tissue (highly magnified). 



their affinities with modern forms ; but the knowledge of 

 this subject has been constantly extending, and a suffi- 

 cient amount of information has been obtained to enable 

 us to say something as to their probable relationships. 

 (Pigs. 51 to 55.) 



The families into which modern ferns are divided are, 

 it must be confessed, somewhat artificial, and in the case 



