1914] PET RY—OPHIOGLOSSUM PENDULUM 177 
dermis soon disappears; before separation from the root stele is 
complete, a few cells of parenchyma appear near the center of the 
xylem mass (fig. 7, C). The number of these increases and a 
definite pith is established (fig. 7, D). A small gap opens through 
the xylem, and closes again almost at once; the phloem is not 
interrupted. The xylem cylinder dilates rapidly and becomes 
oval in section; root steles attach at the points of the oval, leaving 
large “root gaps”’ in the cylinder (fig. 7, L). A third root attaches 
between the two gaps (fig. 7, M), producing a small gap; the three 
gaps close at about the same level. The first strand of the trace 
SO S 
Sasa 3 
ASS 
Fic. 7-—Development of stem stele from a single strand; only the xylem is 
shown: r, tetrarch stele of parent root; rt, root trace; rg, root gap; /s, first strand of 
first leaf; x12, : 
of the first leaf separates from the cylinder at a slightly higher 
level (fig. 7, N). This is essentially the course of development of 
the stem stele of O. vulgatum from a bud. 
In five cases, two strands of xylem of varying shape in cross- 
Section separate from two of the poles of a triarch or tetrarch root. 
Stams of sections of one of these specimens are given in fig. 8. 
Each strand at the point of junction with the root stele has phloem 
On two faces, or surrounding it; the phloem disappears almost 
immediately from the adjacent faces and becomes restricted to the 
“xterior sides of the strands. After an interval the two strands 
