iQiSl 



PETRY—i >l'Il IOC LOSS. I CE. 1 1- 



353 



destruction of the greater portion of the original xylem of the stem; 

 the attendant periderm formation has produced a considerable 

 distortion of the stele. As the leaf trace separates from the stele 

 (fig. 6, C) it is surrounded by a ring of xylem composed on the 

 outer side of accessory secondary wood and on the inner side of 

 centripetal secondary wood. This ring splits into two masses 

 (fig. 6, D), and the leaf trace is cut off and carried out by periderm 



til.. 0. — Transverse sections of a branching rhizome of Bolrychium obliquum: 

 I, injured region; X3-5- 



formation. At a somewhat higher level, the accessory secondary 

 xylem closes across the gap (fig. 6, F). 



At a lower level (fig. 6, £), masses of xylem arise in the pericycle 

 of one of the strands which formed part of the ring surrounding the 

 leaf trace. Similar masses of pericyclic xylem occur outside the 

 accessory secondary wood which closed the leaf gap dig. 6, F). 

 The development at this point results in the formation of a closed 

 ring of xvlem with cambium and phloem on the inside (fig. 6, (-'); 

 at a slightly higher level, this becomes a tangled mass of tracheids 



