Development of the Fern Leaf 23 
’ stalks will be the apex of the former stalk, and the three stalks 
will thus constitute a dichotomous rachis. 
It is thus apparent that each section of rachis in a leaf with 
free flabellate venation consists of the part of some segment sub- 
divided into segments that contained the vein entering the seg- 
ment, and which has become attenuated. This attenuation of 
this part of the segment that becomes the section of rachis may 
take place before, during, or after the subdividing of the segment 
into segments. If before, the segment, until it subdivides into 
segments, will appear merely stalked, and if it be one of the two 
terminating a rachis or petiole of a leaf, will appear raised above 
the other by its stalk. 
It is also apparent that whether the rachises of the leaf with 
free flabellate venation are simple, forked, or otherwise com- 
pound, and whether they bear segments on one or both sides, as 
well as at apex, or at apex only, depends upon which of the leaf’s 
segments subdivide into segments and become attenuate below 
these segments in the course of the leaf’s development. 
There are certain cases in which the compound or partly 
compound leaf with free flabellate venation may resemble or be 
indistinguishable from that with free pinnate venation. For 
example: 
(1) When in the flabellate-veined leaf segments are borne on 
both sides of the rachises, and attenuation of the parts of segments 
of which the rachises are composed has not been very complete, 
so that a small amount of leafy tissue forming a wing remains 
about the vein each of these parts contains, this leaf may re- 
semble or may be indistinguishable from the pinnate-veined leaf 
in which the incisions between the primary branches of the mid- 
