52 



EQUISETALES. 



Group PTERIDOPHTTA 

 (YASCULAR CRYPTOGAMS). 



Class EQUISETALES. 



Perennial plants with underground branclied rhizomes, from 

 which, are given off roots and erect branched or unbranched 

 aerial shoots. The shoots are characterized by the small verticiUate 

 sheathing leaves borne on the slightly swollen nodal regions ; the 

 nodes are separated by longer or shorter internodes. The sporangia 

 occur on specially modified sporophylls or sporangiophores, aggre- 

 gated to form a definite strobilus or spore-bearing cone. 



The Equisetales include the single recent genus lEquisetum and 

 the fossil genera JEquisetites, Phyllotheoa, Schizoneura, Calamites, 

 and Archmocalamites ; the genus JEquisetites is the only one 

 represented in the Yorkshire Oolite flora. 



Family EaUISETACE^. 



An accurate diagnosis of the family Equisetaoese as including 

 the recent Horsetails and species of JEquisetites is practically 

 impossible, as our knowledge of the fossUs is far from complete. 

 The striking similarity of the fossil stems from Triassic, Jurassic, 

 and more recent formations to the widely distributed Equisetums, 

 justifies the inclusion of JEquisetites in the Equisetacese as a type 

 agreeing in habit, and presumably in structural features, with the 

 recent genus; but our information rests solely on external 

 characters, and we know little or nothing as to the anatomy of 

 the fossil Horsetails, nor have we any evidence as to whether the 

 sporangia contained spores of one kind only or were heterosporous. 



