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. 



