EQUISETITES. 55 



leaf - segment is flat or slightly depressed, and the edges in 

 well-preserved specimens bear small protuberances, which may be 

 indications of siliceous deposits in the epidermis. 



The stem or larger aerial branches bore occasional branches at 

 the nodes, about five at each branching node ; the more slender 

 specimens sometimes possess still more delicate branches (e.g. Text- 

 fig. 3). 



Nodal diaphragms occur frequently on the lower part of the 

 internodes of the smaller branches, or as isolated discs ; the 

 diaphragms consist of a central circular area of tissue, from which 

 raliate narrow bands separated by slightly broader spaces. 



Brongniart defined the species in 1828 as follows: " E. caule 

 erecto, simplici, Ia3vi, cylindrico, diametro 2-3 poll, aequali, articulis 

 versus basim approximatis, superne distantibus ; vaginis erectis, 

 cauli arete applicatis, multidentatis, dentibus brevibus, sed in 

 acumine filiformi caduco productis." l 



In the work of Young & Bird (1822) 2 a figure is given of a fairly 

 large Equisetites branch, and additional drawings of the same 

 species occur in the second edition 3 published in 1828. These 

 authors refer to Equisetites as a reed-like plant abundant in the 

 strata exposed in the cliffs opposite High Whitby ; they compare 

 the fossils with Equisetum, and regard the vertical position of the 

 casts as a proof of their occurrence in situ ; they suggest, however, 

 that both stems and matrix may have been transported into their 

 present position. It is interesting to notice that Young & Bird 

 speak of the occurrence of lateral branches, a fact overlooked by 

 later writers. The occurrence of branch-scars protruding through 

 the lower portion of the leaf-sheaths of several specimens fully 

 bears out the conclusion of these authors (vide PL XIX. Fig. 1). 



The casts of Equisetitea columnaria have long been familiar 

 fossils in the Lower Estuarine beds in the cliffs near Whitby 

 and elsewhere ; they often occur in a vertical position in the 

 sandstone, 4 or as flattened carbonaceous impressions on the associated 

 bands of shale. Many writers have expressed the opinion that 

 these Equisetaceous plants contributed largely to the formation 



1 Brongniart (28 2 ), p. 115. 



* Young & Bird (22), pi. iii. fig. 3. 

 3 Ibid. (28), pi. iii. figs. 4-6. 



* Seward (98), p. 72, fig. 11. 



