STIGMARIA 



245 



The regular radial seriation of the secondary xylem- 

 elements is sometimes interrupted by the intercalation 

 of a tangential band of much smaller tracheae, beyond 



Fig. 99. — Stigmaria ficoides. Part of tangential section through wood, showing an 

 outgoing rootlet-bundle. All the tracheides are scalariform. m.r, medullary rays ; 

 J>x, protoxylem of rootlet-bundle. The top of the figure is directed towards the base 

 of the Stigmaria. X 40. Spencer Coll. 150 (now S. Coll. 1469). (G. T. G.) 



which the regular formation of large elements recom- 

 mences. These interruptions no doubt point to a 

 break in the activity of the cambium, but the small- 

 celled layers are not always continuous, and cannot be 

 regarded as marking annual rings. To use Williamson's 



