32 Dr. W. C. Williamson on 



internal organisation was as well preserved as in Witham's 

 specimen. Still later similar deposits were found in various 

 parts of the contiguous district of Halifax. At that time 

 Binney fully accepted Brongniart's erroneous conclusions. 

 About that period my own attention became directed to 

 the same class of objects, and as my researches progressed 

 I discovered what the error was into which Brongniart had 

 fallen. 



In living Cryptogenic plants such as Equisetums, Ferjts, 

 and Lycopods, no trace of a secondary Exogenous Zone, 

 the product of a Cambium layer, was then known to exist. 

 Brongniart interpreted his fossils by what he believed to be 

 characteristic of all the living ones ; hence he adopted the 

 hypothesis that if any of these Carboniferous fossil plants 

 possessed a secondary or exogenous xylem structure they 

 could not possibly belong to the Cryptogamic family. Since 

 his day we have found that this mode of growth exists in 

 the living Isoetes or Quill-worts. I soon discovered that all 

 the extinct Equisetiform Calamites possessed this structure, 

 and as time went by I obtained the clearest evidence that 

 nearly all the Carboniferous Lycopods, the Lepidodendra, 

 the Sigillarice and the Stigmaria were similarly organised. 

 It required a long conflict to convince the disciples 

 of the Brongniartian school of the correctness of these 

 conclusions ; but after a contest of nearly twenty years' 

 duration my views were almost universally recognised 

 as correct. But other and not unimportant questions 

 remained, on which wide differences of opinion existed. 

 In the earlier stages of my investigations, and when my 

 specimens were comparatively few, I arrived at certain 

 conclusions respecting the mode of growth of the Carbon- 

 iferous Lycopods, which were not accepted by some of 

 my botanical friends, especially by Graf Solms-Laubach. 

 Time rolled by without our coming to any general agreement. 

 At length, the specimens in my cabinets having enormously 



