PALEOBOTANY BEERY. 



311 



modern flora. They are represented in the Mesozoic by Coniopteris, 

 Dicksonia and Thyrsopteris, to which Deimstaedtia is added in the 

 Tertiary. 



The Polypodiaceae, which comprise the bulk ot existing ferns and 

 exhibit a very great variety in form and habit, are relatively modern. 

 Some at least of the older Mesozoic species which are referred to the 

 form genus Cladophlebis belong to this family. Cladophlebis which 

 appeared in the Triassic became cosmopolitan in the Jurassic and 

 Lower Cretaceous where 1 it was associated with species of Onychiopsis, 

 Asplenium, Dryopterites, etc. Pteris, Onoclea and other genera are 

 added in the Upper Cretaceous, and a great variety of generic types 



Tig. 5.— Sketch map showing the existing range and the geologic occurrences of the Dipteriaceae. 



appear in the Tertiary (Adiantum, Polypodium, Acrostichum, 

 Oleandra, Woodwardia, etc.) 



PHYLUM ARTHROPHYTA. 



The Arthrophyta constitute a well-marked phylum and comprise 

 plants ranging in size from herbaceous forms to large trees and 

 found from the oldest horizons containing land plants down to the 

 present. They are characterized by invariably articulated and pre- 

 vailingly ribbed stems, with the leaves in whorls (verticillatc) at the 

 nodes, free or more or less connate, dichotomously compound in the 

 earlier groups (Pseudoborniales, Protocalamariaceae), palmately 

 lacinate in some Sphenophylleae, progressively reduced during the 

 history of the phylum until in the modern forms the stems and 



