74 Maidenhair Spleenwort 
of the leaf containing the section of primary midvein between 
that pair of primary branches and the pair next above becomes a 
section of rachis. The primary midvein thus becomes merged 
in a rachis, remaining visible asa midvein in the leaf’s apical section 
only. While pinne and primary branches of this midvein are 
separating from the base of the apical section, this section and this 
midvein lengthen at apex, the midvein sending out additional 
primary branches, but this takes place slowly; the apical section, 
therefore, is usually rather short. One or more pinn@ are usually 
to be seen in the process of forming on and of separating from it. 
In the very young leaf the pinne newly formed are often, like 
the leaf-blade newly formed, obcordate, with their midveins not 
developed beyond two simple primary branches. Such pinne 
resemble the pinne of Asplenium Clutei, Gilbert.* The various 
forms of the early pinne can be seen from Plate XV. As the leaf 
develops, the pinne lengthen and broaden, gradually assuming 
their mature forms, their midveins lengthen and send out addi- 
tional primary branches, and these midveins’ primary branches 
mostly become more or less complex. 
The pinne are usually crenately toothed or lobed, but, occa- 
sionally, incised. The so-called “‘var. incisum” is based upon 
monstrously developed sterile leaves with deeply incised pinne. 
* See Fern Bulletin, 8: 62-63. 1900. 
