I06 THE HISTORY OF CEEATION. 



was already developed during the palaeolithic period out of 

 other ferns by adaptation to an aquatic Hfe. 



The fourth class of ferns is formed by the Tongue Ferns 

 (Ophioglossse, or Glossopterides). These ferns, to which 

 belongs the Botrychium, as well as the Ophioglossum 

 (adder's-tongue) of our native genera, were formerly con- 

 sidered as forming but a smaU subdivision of the frondose 

 ferns. But they deserve to form a special class, because 

 they represent important transitional forms from the 

 PterideEB and Lepidophytes towards higher plants, and 

 must be regarded as among the direct progenitors of the 

 flowering plants. 



The fifth and last class is formed by the Scale Ferns 

 (Lepidophytes, or Selagines). ■ In the same way as the 

 Ophioglossae arose out of the frondose forms, the scale ferns 

 arose out of the Ophioglossse. They were more highly 

 developed than all other ferns, and form the transition to 

 flowering plants, which must have developed out of them. 

 Next to the frondose ferns they took the largest part in the 

 composition of the palaeolithic fern forests. This class. also 

 contains, as does the class of reed ferns, three nearly related 

 but still very different orders, of which only one now exists, 

 the two others having become extinct towards the end of 

 the carboniferous period. The scaled ferns still existing 

 belong to the order of the club-mosses (Lycopodiacese). 

 They are mostly small, pretty moss-like plants, whose 

 tender, many-branched stalk creeps in curves on the ground 

 like a snake, and is densely encompassed and covered by 

 small scaly leaves. The pretty creeping Lycopodium of 

 our woods, which mountain tourists twine round their 

 hats, is known to all, as also the still more delicate 



