THE EQUISETALES (INCLUDING SPHENOPHYLLALES) 273 



to alternation. As a result of this condition the leaf traces, which 

 here, as in the modern type, originate from the lower internodal 

 strand, subtend, not a gap above the nodal wood, but the strand 

 of the upper internode. It is thus clear that the older condition 



FIG. 196 a, b, c, and d. Diagrams illustrating the relations of the bundles in 

 Equisetum and Archeocalamites . Explanation in the text. 



for the Equisetales is one in which there cannot possibly be a gap 

 corresponding to a leaf, even above the so-called nodal wood. A 

 radial view of the situation in Archaeocalamites makes the topog- 

 raphy still more clear, and this is furnished in D. Obviously on 

 historical grounds the Equisetales are without foliar gaps and 



