1915] PETRY—OPHIOGLOSSACEAE 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 
G. 6.—Transverse sections of a branching rhizome of Botrychium obliquum: 
i, injured region; 3.5. 
formation. At a somewhat higher level, the accessory secondary 
xylem closes across the gap (fig. 6, F). 
At a lower level (fig. 6, E), 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 (fig. 6, F). 
The development at this point results in the formation of a closed 
ting of xylem with cambium and phloem on the inside (fig. 6, G); 
at a slightly higher level, this becomes a tangled mass of tracheids 
