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 flagellif orm ; and its base from truncate 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. 



