THE STEM OF CALAMITES 31 



Occasionally, in comparatively young stems, we find 

 tangential divisions beginning in the inner cells of the 

 cortex, and it is highly probable that this was the 

 first commencement of the periderm-formation which 

 attained such a great extent in the older stems. The 

 trunks of the larger Calamites must have had a regular 

 bark, like that of our forest-trees, but thicker than in 

 most of the latter. 



3. Branching. — The next question to be considered 

 - is that of the branching of the stem. It is very common 

 to find the bases of branches in connection with the main 

 axis. The section represented in Fig. 9 is a tangential 

 one, passing through the base of a branch, where it 

 joins the primary wood, so that its tissues are shown in 

 continuity with those of the stem which bears it. The 

 insertion of these branches is very regular. They are 

 always placed immediately above the node, and usually 

 between two of the outgoing leaf-trace bundles (Fig. 9). 

 Sometimes a branch may be nearly or quite as large 

 as the main stem, repeating all the characteristics of 

 the latter ; in other cases we find lateral branches 

 which are very small in comparison with the main 

 stem ; 1 such lateral shoots often occur in considerable 

 numbers in a verticil. It is an interesting point that 

 these little branches were in many cases abortive, as 

 shown by the fact that we often find their bases com- 

 pletely enclosed in the wood. At the same time that 

 this was proved for the English specimens, Renault 



measures," Part ix., Phil. Trans. 1878, Part ii. Plate xx. Figs. 14 and 15 ; 

 also in Seward's Fossil Planls, vol. i. Fig. 78. 



1 The medullary casts shown in Figs. 2 and 3 illustrate these two cases. 



