CHAPTER XVII. SUCCESSION OF VEGETABLE LIFE. 393 



dodendrons, Sigillarias, Calamites and Ferns become wonderfully 

 numerous, and many of the species attain gigantic dimensions. 

 At no period before or since have the vascular cryptogams 

 attained such a wonderful development. It was emphatically 

 the age c2 Pteridophytes. The Lepidodendrons, Sigillarias and 

 Calamites were marsh plants, and it was probably chiefly from 

 their remains that the immense coal beds of the period were 

 produced. The Ferns and Conifers, though numerous, contrib- 

 uted comparatively little to coal formation, because they were 

 high-land plants. During this age, also, a new gymnospermous 

 type — the Cycads — was introduced. 



Plants of the Mesozoic. With the opening of the Mesozoic 

 or Reptilian age, we find the species and many of the genera 

 have again changed, and forest vegetation presents quite a dif- 

 ferent aspect. The giant Sigillarias and Lepidodendrons have 

 passed away. Conifers have increased in abundance and 

 variety, and many of the species have a more modern aspect. 

 The Calamites and Ferns still hold their own and tree-ferns are 

 abundant, while the Cycads, which in the Carboniferous had 

 attained but little importance, have wonderfully increased and 

 become the predominant type of forest vegetation. But no new 

 types were added until the latter part of the Jurassic, when a few 

 Monocotyledons allied to the screw-pines and grasses made 

 their appearance. Vascular cryptogams and gymnosperms still 

 ruled the vegetable world. 



But in the latter part of the succeeding period, the Creta- 

 ceous, a great and apparently sudden change takes place in the 

 flora. The Conifers reach the culminating point of their devel- 

 opment in this and the succeeding age, and are represented by 

 such modern types as the Yews, Pines, Junipers, and the noble 

 Sequoias, while the Cycads, on the other hand, begin to decline. 

 The Ferns are still abundant, though less so than formerly, and 

 are now represented by such modern genera as Dicksonia, 

 Gleichenia, Aspidium and Onoclea. It is interesting to note 

 that one species, Onoclea sensibilis, has persisted throughout all 

 the profound changes that have taken place from Cretaceous 

 times down to the present, and is still abundant. 



But the most conspicuous change is the great increase in the 

 number of Monocotyledons, and the appearance of Dicotyle- 



