75 



Page6o, Sphenophyllum plurifoliatum, Williamson & Scott.* 

 Transverse section of a petrified stem. The structure of the stem of 

 Si^henophyhuni is of gseat interest from the fact that it resembles 

 closely that of the root of many other plants. There is no pith, and 

 consequently no pith-casts. The central tissue is the wood. The 

 triangular, small-celled, inner portion of the wood is the primary 

 wood, which consists of three radiating arms, the small -celled, first 

 formed elements being at the extremities of the arms. The secondary 

 wood forms a broad zone of large celled, radially-arranged elements, 

 external to the primary wood. More externally still the ring of 

 bark is seen. From the Lancashire coalfield. X about 20. (Pho- 

 tomicrograph by Mr. Tarns.) . 



CORDAITALES. 



Our last great group, the Cordaitales, were large trees, in many 

 respects allied to our modern Pines and Firs, though very different 

 from them in appearance. The stems of Cordaites were tall and 

 much branched, and the leaves were usually long and strap-shaped, 

 with a characteristic parallel nervation. 



Page 61. Cordaites angulosostriatus, Grand 'Eury.* Part 

 of a leaf showing the shape and parallel nervation. From the Som- 

 erset coalfield. Slightly reduced. 



Page 62. Cordaites angulosostriatus, Grand 'Eury.* The 

 tip of a leaf, slightly enlarged to show the numerous parallel nerves. 

 From the Somerset coalfield. X f. 



Page 63. Cordaites sp. A transverse section of a petrified 

 stem of Cordaites, showing a pith internally and a large ring of wood. 

 The structure of the wood is much like that of a Pine. The pith 

 was hollow, but is here filled with a cast of sandstone. From the 

 South Lancashire coalfield. \ Natural size. 



Page 64. Cordaites sp. A pith-cast in sandstone. These 

 pith-casts, formerly termed Artisia or Siernbergia, have numerous 

 constrictions at very short intervals. This is due to the fact that 

 the hollow pith-cavity, in the living state, was bridged at short 

 intervals by diaphragms of tissue, much like the pith of a branch of 

 the Walnut tree. From the South Lancashire coalfield. Natural 

 size. 





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