1914] PETRY—OPHIOGLOSSUM PENDULUM 189 
of the sporangia. Farther up the spike, where the ridge of sterile 
tissue which extends into the spore mass is well developed, the 
strand occupies a position well within this ridge (fig. 16, B). There 
is no branching of the marginal strand below the first few sporangia; 
but between the third and fourth sporangia, a short lateral branch 
extending halfway to the edge of the spike usually occurs. Similar 
strands occur between all the sporangia above this point (fig. 16, 
They consist in cross-section of 10 or 12 tracheids, and occupy 
the center of the thin wall separating adjacent sporangia. Near 
the margin of the spike they spread out in the shape of a fan and 
end blindly (fig. 16). The central 
strands are reduced by fusion to a 
single strand when the tip of the 
spike is reached. Between the ter- 
minal sporangia this splits into two 
Strands which run out above the 
sporangia and end in the fan-shaped 
arrangement described above. 
The strands of the peduncle and 
of the median region of the spike 
show the same structure as those of 
the blade of the leaf , but the bundle Fic. 16.—Diagrams of vascu- 
sheath is much less developed. In _ ler system of the _, cpr 
: itudinal section; B, transverse 
- . i. ee coe erate se C, transverse 
. section in plane aa; X4.5. 
Protophloem is on the adaxial side 
of the xylem, but the later developed phloem elements may extend 
in the shape of a U about the xylem, which is always endarch. In 
the fan-shaped portion of the strands the phloem cannot be 
distinguished ; there is no distinction between protoxylem and 
metaxylem. 
Discussion 
The most striking characteristic of the anatomy of this species 
the extreme variability of certain structures. The number of 
_Protoxylem strands of the root and the number of strands consti- 
tuting the leaf trace vary almost directly with the size of the organs 
concerned. The external conditions which determine whether the 
is 
