Silvery Spleenwort 103 
two veins each of which stands, in the relation of a primary 
branch or of a superior basal primary branch of a primary 
branch to a midvein, the sorus opening toward the midvein. 
On such veins as stand in one of these relations to each of 
two midveins two sori are often borne, one opening toward one 
midvein, the other toward the other midvein. These sori are 
either distinct (diplazioid) or connate at the outer end (athyri- 
oid). For instance: 
The midveins of the pinne’s segments are also primary 
branches of the pinnz’s midveins, hence diplazioid and athyri- 
oid sori, or at least the opposed parts of such sori, often occur 
on their superior basal primary branches. Such sori are found 
particularly in the small uppermost pinne and the apices of 
the larger pinnz, where the pinne’s midveins are more dis- 
tinctly midveins (are less merged in midribs), than elsewhere. 
In the pinne in which the primary branches of the midveins of 
the pinnz’s segments are simple, the only midveins are the mid- 
veins of the pinne’s segments and the midveins of the pinnez, hence 
such sori occur only as above described—+.e., next the pinne’s 
midveins or midribs, on the superior basal primary branches of 
the midveins of the pinne’s segments, which in these pinne 
are the only veins standing in the required relation to each of 
two midveins (Pl. XXV, Fig. 3). In the pinne in which the 
midveins of the pinnz’s segments bear branches, and so represent 
incipient or well-defined midveins of the segments’ lobes, such 
sori occur on their superior basal branches (PI. XXV, Fig. 2). 
In all the specimens of this fern that I have examined, I have 
not been able to find the opposed parts of any diplazioid or athy- 
rioid sori on any vein that did not stand in such relations to two 
midveins as to lead one to expect two sori upon it, or either of 
