Narrow-Leaved Spleenwort 67 
the two sori may continue, in which case they will diverge, each 
following the veinlet nearest the midvein toward which this 
sorus opens, as that veinlet is the only one of the two that stands 
in one of the required relations to that midvein. At the lower 
end, the sorus that opens toward the pinna’s midvein cannot 
extend farther than that midvein, as no sorus in this fern extends 
at base farther than the midvein toward which it opens, but the 
other sorus may extend down the pinna’s midvein to the leaf’s 
primary midvein, toward which this sorus opens. It will be seen 
that only such parts of the sori are diplazioid as extend along the 
same part or the whole of the upper basal primary branch of the 
pinna’s midvein. 
