XV] LEPIDODENDRON 145 



and broader and more elongated spaces ; it is interrupted here 

 and there by an outgoing leaf- trace, as at It 1 and It 2 in fig. 162. 

 The secretory zone is succeeded by a homogeneous inner cortex 

 like that described in L. vasculare ; part of this region is seen 

 at the upper edge of fig. 162. The broad middle cortex, which 

 is separated from the inner cortex by a sharply defined 

 boundary, is composed of rather small lacunar parenchyma- 

 tous tissue consisting of sinuous tubular elements interspersed 

 among isodiametric cells of various sizes (fig. 166, p). In 

 the middle cortical region the leaf-traces pursue an almost 



Fig. 165. Lepidodemlivn fuliginosum. Leaf-trace: x, xylem; «, secretory zone. 

 (Binney Collection, Cambridge.) 



horizontal course; one is shown in fig. 164, in oblique longi- 

 tudinal section, in a reversed position ; the xylem, x, should be 

 on the inner side of the secretory tissue, s. The clear space 

 between the two parts of the vascular bundle was originally 

 occupied by a few layers of parenchymatous cells, as seen in the 

 transverse sections, figs. 165 and 166. In some specimens the 

 leaf-traces pass through the middle cortex in a much more 

 vertical course, as shown by the section represented in fig. 165. 

 This section illustrates the structure of a typical leaf-trace with 

 unusual clearness ; it shows the tangentially elongated group of 

 xylem, the strand of tissue which occupies the position of phloem, 



