Walking Leaf 133 



or obcordate blade usually follows it. The order of forms of the 

 blade in the scale of leaf -development is as follows: Spatulate, 

 obcordate or obreniform, cuneate and trilobed or broadly cuneate- 

 rhomboidal, roundish-ovate with truncate base, ovate, ovate-ob- 

 long, ligulate, and lanceolate. The blade's apex changes from 

 obtuse to flagelliform; and its base from trimcate to cordate, 

 auriculate or hastate, and finally, although rarely, becomes de- 

 veloped laterally into long-drawn-out lobes, which are similar to 

 the flagelliform upper part of the leaf, and sometimes, like it, pro- 

 liferous at apex. 



Although connate at base with the main part of the leaf- 

 blade, these lateral lobes are in reality partly formed pinnae.* 

 In them, as well as in the flagelliform upper part of the leaf- 

 blade, is shown the tendency of this fern's leaf to become 

 attenuate and proliferous at its apices, whether primary or 

 secondary. 



The spatulate leaf-blade contains a simple or once-forked 

 vein. The obcordate and the obreniform each contain a once- 

 to twice-forked vein, and the trilobed and the rhomboidal each 

 a midvein with two simple or once-forked branches at apex and 

 two below. The development of the midvein continues in the 

 succeeding leaves. The midvein is contained finally in a midrib. 



The veins are free at first, f The formation of areolae appar- 

 ently begins as the blade becomes truncate at base, when two 

 or more of the midvein' s branches unite next the midvein. In 

 succeeding leaves the midvein's branches become more and 

 more anastomose until they form a network that extends nearly 

 to the leaf-blade's margin. They are united in such a way that 

 the veinless border of the blade seems to cut the network ; appar- 



* See page 12 t See page 18. 



