336 



DR D. H. SCOTT ON THE 



kathodic side of B is presumably the one destined to unite with that leaf-trace 

 (diagrams 1-3) ; in the lowest section (diagram 4) it has disappeared, which may be 

 due to its fusion with B, or more probably to mere destruction of tissue ; for the fusion, 

 according to the analogy of other strands, would not be likely to take place so high up. 

 Lastly, the remaining small bundle, c, which appears in all four sections, is in all 

 probability the reparatory strand ready to unite with C, which it is already approaching 

 in the lowest section (diagram 4). In other words, if we trace the course of the 

 bundles from below upwards, we may say that each circum-medullary strand branches 



Diagram 3 (K. 629). 



at regular intervals ; the one branch, that on the anodic side, becomes the leaf-trace 

 and passes out, while the other continues its course up the stem as a reparatory strand, 

 until the next leaf of the orthostichy has to be supplied. It is, however, probable that 

 subsidiary unions between the bundles also occurred. 



The course of the bundles, so far as it has been determined, thus appears to be 

 identical with that found in the stem of Lyginodendron oldhamium* 



The position of the xylem-strands in the three transverse sections of the Williamson 

 specimens also points to a 2/5 phyllotaxis. The order of the sections from above 

 downwards appears to be : — 1378, 1380, 1379. 



The internodes of the stem were probably short, as is indicated by the rapid succession 



* Williamson and Scott, " Further Observations on the Organization of the Fossil Plants of the Coal-Measures." 

 Pt. III. Lyginodendron and Heterangimn, Phil. Trans. Roy. Soc, vol. 186 (1895), B, p. 711. 



