270 PTERIDOPHYTA. [CH. 



largest stem in the British Museum collection has inter- 

 nodes about 14 cm. long and a diameter of about 5 cm. In 

 some cases the stem casts show irregular lateral projections in 

 the neighbourhood of a node, but there is no evidence that the 

 aerial shoots of this species gave off verticils of branches. In 

 habit E. columnaris probably closely resembled such recent 

 species as Eqidsetam hiemale L., E. trachyodon A. Br. and 

 others. 



The stems often show a distinct swelling at the nodes ; this 

 may be due, at least in part, to the existence of transverse 

 nodal diaphragms which enabled the dead shoots to resist 

 contraction in the region of the nodes. The leaf-sheaths 

 consist of numerous long and narrow segments often truncated 

 distally, as in fig. 58, B, and as in the sheath of such a recent 

 Horse-tail as E. ramosissimiim shown in fig. 58, G. In some 

 specimens one occasionally finds indications of delicate acumi- 

 nate teeth extending above the limits of a truncated sheath. 

 Brongniart speaks of the existence of caducous acuminate teeth 

 in his diagnosis of the species, and the example represented 

 in fig. 58, jB, demonstrates the existence of such deciduous 

 appendages. There is a very close resemblance between the 

 fossil sheath of fig. 58, B, with and without the teeth, and 

 the leaf-sheath of the recent Equisetum in fig. 58, C. In 

 some specimens of E. columiiaris in which the cast is covered 

 with a carbonaceous film, each segment in a leaf-sheath is 

 seen to be slightly depressed in the median portion, which 

 is often distinctly marked by numerous small dots, the edges 

 of the segment being flat and smooth. The median region 

 is that in which the stomata are found and on which deposits 

 of silica occur. 



6. Equisetites Beani (Bunb.). Figj^. 60 — 62. 



Bunbury^ proposed the name Calamites Beani for some 

 fossil stems from the Lower Oolite beds of the Yorkshire coast, 

 which Bean had previously referred to in unpublished notes as 

 C giganteus. The latter name was not adopted by Bunbury 



1 Bunbury (51) p. 189. 



