5 2 Polypody 



become especially lengthened, or perhaps more than mere lobes, 

 is due the abruptly narrowed appearance of the leaf-blade at 

 apex, common in this fern's leaves. 



The blade at first is obtuse at apex, but as it grows large and 

 long it becomes acute or acuminate. Sometimes, although rarely, 

 the segments also become acute or acuminate. Acute or acuminate 

 apices in the segments are often correlated with monstrous de- 

 velopment of the leaf, but occur also in leaves otherwise typical, 

 particularly in unusually large ones. Their occurrence in the 

 latter leaves is in accordance with a tendency, common in many 

 ferns with pinnate venation, to lengthen and point the leaf-blade 

 and its segments, as these enlarge in developing, and such leaves 

 are at best doubtfully abnormal, although undoubtedly unusual 

 in P. vulgare. 



The primary branches of the leaf's primary midvein develop, 

 while the segments are forming, into the segments' midveins. 

 Their branches are usually simple in the young very small leaves. 

 In the large, or at least in the older leaves, these branches bear 

 branches, and when the segments become incised in monstrous 

 development of the leaf, often appear as well-defined midveins 

 in the segments' lobes. 



The superior one of the two basal primary branches of the 

 primary branches of the leaf's midveins is usually lower but 

 sometimes higher than the inferior, and sometimes opposite it. 



On a superior one each sorus is borne. What seems at first 

 an exception to this occurs sometimes near the leaf's apex, 

 where the primary midvein, emerging from the rachis, appears 

 as a midvein in the leaf's apical section, and the series of 

 son belonging to it consequently appear. Here the superior 

 basal primary branch of the midvein of some one of the leaf's 



