STIGMARIA 



247 



direction, for it is on the inner edge of the secondary 

 cortical zone that remains of the delicate phellogen 

 can be traced. The tissue thus formed cannot have 

 been of the nature of cork, for the outer tissue shows 

 no sign of withering, and some of its cells had some- 

 times undergone tangential division, as if starting a 



Fig. 100. — Stigmariaficoidcs. Part of transverbe section, to show base of a rootlet, /a, 

 periderm of main axis ; o.c, outer cortex (including hypoderma) of main axis and of 

 rootlet ; i.c, inner cortex, x, xylem of rootlet ; r>, tracheites passing out to rootlet. 

 X about 15. (G. T. G.) 



new, more external phellogen. In many of the Car- 

 boniferous plants the formation of secondary cortex 

 played a much more important part than is usually 

 the case in recent vegetation, and though we use the 

 words " periderm " and " bark," it is certain that many 

 of the structures thus indicated were very different in 

 nature and function from the recent tissues which 



