54 DR. W. C. Williamson on 



tracheids were accumulated at the base of the central 

 stem of the Lepidodendon ; but the question now arose, how 

 did they get there ? My first idea was that they could not 

 have existed there in such numbers when the tree was a 

 young and small sporophyte ; in which case they must have 

 multiplied as the various parts of the plant grew larger. 

 But against this explanation came the difficulty of under- 

 standing how additional leaves and leaf-traces could be 

 intercalated amongst those already arranged in a system of 

 geometrically disposed spirals. The longer I pondered 

 this question the less I was able to suggest any solution of 

 it. Utterly baffled, I then turned to Solms-Laubach's 

 hypothesis, to see if it reduced the number of the difficulties 

 to be overcome. 



As I have already observed, my dissentient friends agree 

 with me so far as the more conspicuous facts stated above 

 are concerned, and the existence of which is clearly demon- 

 strated in each of my six tables. They say that the 

 increase in descending order of the tracheids and leaves 

 never could have been developed by any known process of 

 growth in the same branch. In p. 229 of his Fossil Botany, 

 (English Translation), Solms-Laubach puts very fairly and 

 clearly what my views were, but he then proceeds to give 

 his reasons for rejecting them. He says, " It is to be remem- 

 " bered that we must not simply compare the terminal 

 " ramifications of the head of a tree with the still young and 

 " growing ends of the main shoot or of its subordinate 

 " branches. The central strand in the main shoot and in 

 " the branches may and will have had a very different 

 " diameter at the beginning of the growth in thickness, from 

 " that of the later generations of branches, the last of which 

 " may have had no growth of the kind." With these views 

 my colleague, Dr. Scott, entirely agreed, an additional reason 

 for submitting their hypotheses to a careful investigation. 

 But whilst I arrived at the conclusion that their views 



