20 Development of the Fern Leaf 
leaf with flabellate free venation into segments, occurs between 
the two vein-branches formed by the first forking of the vein 
entering the blade or segment. Each new segment thus con- 
tains one of these branches, with its ramifications, if any. If no 
ramifications exist, some may appear afterward, or, if some exist, 
more. There are also cases in which, coincidently with the fork- 
ing of the vein that enters each segment, and before either of the 
two branches formed by this forking fork, an incision subdivid- 
ing that segment into segments occurs. The latter cases are 
analogous to those in which the venation of the leaf is pinnate 
and incisions occur between the primary branches of the leaf’s 
midveins coincidently with the 
formation of these branches 
and while they are still simple; 
=} 
ee 

Fic. 7. Fic. 8. 
and in both sorts of cases the leaf-blade appears to be made up 
of lobes containing each a simple vein.* 
In Figs. 7 and 8, segments of a leaf with free flabellate 
venation are shown in different stages of subdivision. In Fig. 7 a 
the beginning of the incision by means of which the segment is 
to subdivide is barely indicated. In Fig. 86 the incision is pro- 
nounced. In Fig. 7cde the incision has extended nearly far 
enough to render one (e) of the two new segments distinct, and 
* See page 16. 
