Silvery Spleen wort 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 mid veins 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 mid veins of the pinnae's segments are also primary 

 branches of the pinnae'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 pinnae and the apices of 

 the larger pinnae, where the pinnae's midveins are more dis- 

 tinctly midveins (are less merged in midribs), than elsewhere. 

 In the pinnae in which the primary branches of the midveins of 

 the pinnae's segments are simple, the only midveins are the mid- 

 veins of the pinnae's segments and the midveins of the pinnae, hence 

 such sori occur only as above described — i.e., next the pinnae's 

 midveins or midribs, on the superior basal primary branches of 

 the midveins of the pinnae's segments, which in these pinnae 

 are the only veins standing in the required relation to each of 

 two midveins (PI. XXV, Fig. 3). In the pinnas in which the 

 midveins of the pinnae'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 



