60 THE THEORY OF EVOLUTION 



plants (not seed-bearing). But even the constant 

 absence of spore-heaps by itself is no proof that the 

 leaves belong to a seed-bearing plant, since ferns can 

 propagate themselves purely vegetatively by stolons 

 and offsets. 



Lepidodendrons, Sigillaria, and Cordaites die out 

 in the Old Red Sandstone that is in the formation im- 

 mediately succeeding the Carboniferous. 1 As separate 

 individuals and species here for the first time appear 

 clear remains of Ginkgo trees, also Conifers (Walchia) 

 which are related to the Araucarias 2 and Cycads. 



In the Permian limestone the development of 

 the new forms commences vigorously, the gigantic 

 Pteridophytes and the Cordaites have disappeared, 

 so that there is a sufficient reason for beginning, with 

 the Permian limestone, a new period the Mesozoic 

 which shall be ' the era of the Gymnosperms/ 



Angiosperms, i.e. flowering plants with covered 

 seeds, which, as Monocotyledons and Dicotyledons, 

 form the great bulk of our present flora, are absent in 

 the Mesozoic period. The groups of Gymnosperms 

 develop more and more the forms which approximate 

 nearest to our present ones. In the Chalk our species 

 are already to be found. 



In the lower Chalk there appear the first remains 

 of flowering plants : therewith begins the Csenozoic 



1 In the Red Sandstone we meet again with some traces. They appear 

 then, however, to be entirely extinct, i.e. leaving no successors even of 

 different appearance. 



2 Araucarias are represented by the so-called ' monkey puzzles ' which 

 are frequently cultivated. 



