Development of the Fern Leaf 



19 



In the leaf with pinnate anastomose venation, the incisions by 

 means of which segments are formed occur, as in the leaf with 

 pinnate free venation, between the primary branches of the leaf's 

 midveins, and the midveins of each of these segments start, as 

 in the latter leaf, from the primary branch, as a base, contained 

 within the segment. 



In Fig. 5 is shown the section of a leaf with pinnate anasto- 

 mose venation in which segments have begun to form, with the 

 midveins of these segments 

 not yet evident. In Fig. 6 

 is shown a longitudinal sec- 

 tion of the segment of a leaf 

 with similar venation, partly 



Fig. 5. 



Fig. 6. 



formed segments on one side of the midvein, and the midveins 

 of these segments evident. 



In the leaves with free fiabellate venation, each simple leaf- 

 blade and each segment of each compound leaf-blade is entered 

 at base by a vein which, instead of forming a midvein, either 

 forks once or is dissipated into forking veinlets: if the latter, 

 the successive veinlets, excepting the two first, which are formed 

 by the forking of the primary vein, are formed by the forking of 

 the veinlets preceding them. 



Each incision subdividing the simple blade or segment of a 



