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. 7 a (PL XXXI), with the secondary 

 segment, Fig. 8 a ; and the secondary segment, Fig. 6 b (PL XXXI), 

 with the tertiary segment, Fig. 2 b (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. 



