Maidenhair 39 
the primary branches of the midveins.* By a deepening of the 
one next the basal primary branch, which brings its base between 
this branch and the midvein itself, the incision described above, 
that divides the leaflets into two in the development of the leaf, 
is formed; since that incision occurs between the vein-branches 
formed by the first forking of the vein that enters the leaflet, and 
since the basal primary branch of a unilateral midvein and the 
midvein itself represent those branches. This applies both to 
those leaflets possessing only one midvein and to those possessing 
two midveins, since in the latter case either of the two may be 
regarded as the basal primary branch of the other. 
The incisions between the primary branches of the midveins 
suggest the lines along which future development, normal or 
monstrous, of this plant’s leaf may follow. The lobes which the 
incisions form can be regarded as partly formed leaflets, and it 
would not be surprising if at any time the incisions should deepen 
sufficiently to render these leaflets distinct. It has been seen that 
the basal incision already deepens at times (in the development 
of the leaf’s form), sufficiently to render the basal one of these 
leaflets distinct. 
* This is best seen in the sterile leaves. In the sporophylls an indusium occasionally 
extends over the tops of several primary branches, so that no incisions occur between those 
branches. 
