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Proceedings of the Royal Society of Edinburgh. [Sess. 
slightly flexuous, but those immediately outside of them are very regular. 
They also show scalariform thickening. 
The leaf trace, as seen in transverse section in its passage through the 
secondary xylem, consists of a small oval mass of narrow tracheids, of 
Lepidodendron Pettycurense , Kidston. Transverse section of stele, a , primary xylem ; a', protoxylem ; b, secondary xylem. 
