122 Marginal Shield Fern 
segments at similar stages of development but belonging to 
different series are more or less alike. For example, compare 
the primary segment, Fig. 7a (Pl. XXXI), with the secondary 
segment, Fig. 8a; and the secondary segment, Fig. 6b (Pl. XXXT), 
with the tertiary segment, Fig. 2b (Pl. XXXII). 
As stated in the synoptical description of this fern, leaves 
sometimes occur with the tertiary segments more highly developed 
than in those figured. The scope of the leaf’s development 
and the fact that sori appear, at least sometimes, on the leaf at 
an early stage of its development, have occasionally misled fern 
students into giving different, distinctive names to the plants 
at different stages of the leaf-development. 
It will be seen from the figures that the long acuminate 
apices of the leaf-blade, which are so conspicuous a feature of 
the mature leaves that they have almost come to be looked upon 
as an integral part of the plant’s makeup, are lacking in the early 
stages, and are gradually formed later in accordance with a 
tendency of the leaf-blade itself and the segments of its succes- 
sive series to lengthen and become more and more pointed at 
apex as they become more and more complex. This tendency, 
so marked in this fern, is common in many others, and especially 
in those with pinnate venation. 
