1914] PETRY—OPHIOGLOSSUM PENDULUM 181 
the gap in the cylinder above the insertion of a root might be inter- 
preted as the beginning of the leaf gap; but in very many cases 
openings of an exactly similar nature occur when only a root is 
involved. These gaps close in the same manner as leaf gaps; for 
convenience they may be referred to as root gaps. 
Fic. 11.—Stele of mature rhizome, showing various openings in the cylinder; 
the xylem is shown: rg, root gap; rt, root trace; ig, incidental gap; /g, leaf gap; 
ls, leaf strands; X4.5. 
In addition to these, openings not related to outgoing strands 
often occur in the cylinder (fig. 11, B-F). These incidental gaps 
Sometimes occur at the margin of a leaf gap; a strand separates 
from the margin of the gap, runs parallel to it for a time, and later 
