244 LYCOPODIALES [CH. 



surface is a band of conspicuous cells, b, characterised by dark 

 contents suggesting very imperfectly preserved fungal hyphae, 

 but the nature of the substance filling the cells cannot be made 

 out with certainty. It is, however, interesting to find that this 

 dark band constitutes an obvious feature (fig. H, b); its position is 

 comparable with that of the dark-walled cells in the outer 

 cortex of rootlets. A short distance internal to this dark band 

 tangentially elongated cells form the outermost elements of the 

 secondary cortex ; these become gradually narrower towards the 

 interior and pass into radial series of smaller cells of uniform size, 

 as seen on the inner edge of fig. 210, G. At the inner boundary 

 of this tissue, just below the region shown at the bottom of the 

 drawing, was situated the phellogen. Such traces of tissue as 

 occur on the inner side of the line where splitting has usually 

 occurred, consist of thinner elements with recently formed 

 tangential walls and probably represent an early stage in the 

 development of phelloderm. 



A much older section is shown in part in fig. 210, E. The 

 secondary xylem cylinder, St, is shown in the lower part of the 

 section ; beyond this is a band of secondary tissue which reaches 

 in some places a breadth of 6 cm. The greater part of this 

 tissue consists of phelloderm of very uniform structure made up 

 of radial series of cells : this is interrupted in most parts of the 

 section by a gap crowded with intruded rootlets (a portion of 

 this is enlarged in fig. 210, D). Beyond this gap the secondary 

 tissue consists of radial series of cells characterised by the 

 considerable tangential elongation of many of the elements, 

 precisely like the tissue figured by Williamson. In all pro- 

 bability the gap represents a line of weakness due to the 

 phellogen, and if this is the case it is clear that in an old 

 Stigmaria the phelloderm exceeded in amount the tissue formed 

 external to the phellogen. The secondary tissue on the inner 

 side of the phellogen is characterised by numerous irregular 

 concentric lines superfically resembling rings of growth in the 

 wood of a Conifer: these are, however, not the result of any 

 periodic change in external conditions, but are apparently due 

 to crushing of the tissue and are possibly, to some extent, the 

 result of the presence of secretory strands like those in the 



