Polypody 53 



segments sometimes is once-forked and bears a sorus at each of 

 its two apices. The presence of both these sori can, however, be 

 accounted for. The presence of the sorus on the veinlet nearest 

 the segment's mid vein is explained, if that veinlet is regarded 

 as the superior basal primary branch of the primary branch of 

 the segment's midvein. The presence of the sorus on the other 

 veinlet also is explained, if this veinlet is regarded as merely an 

 extension of the superior basal primary branch of the seg- 

 ment's midvein, and so (since the segment's midvein is a pri- 

 mary branch of the leaf's primary midvein), as a part of the 

 superior basal primary branch of a primary branch of the pri- 

 mary midvein. Occasionally the two veinlets become connivent 

 at apex, and the two sori coalesce, forming one, which is borne on 

 the veinlet' s connivent apices. 



Sometimes occasional areolae occur in the leaf at various 

 stages of its development. 



The veins are clubbed at apex and appear to pierce the face 

 of the leaf: their tips are visible as stramineous spots on the 

 leaf's upper surface at every stage of leaf -development. 



The leaf often becomes monstrously developed. "Var. Cam- 

 bricum" Moore, and many other so-called varieties of this species, 

 are based upon monstrously developed forms of the leaf. 



