l62 STRUCTURE AND LIFE HISTORIES 



produced by the sterilization of spore-bearing leaves. 



Fig. 122. — Walking fern (Camptosorus rhkophyUus). The smaller, 

 lower plant originated at the tip of a leaf of the larger plant, and one of its 

 leaves has, in turn, struck root. 



The interesting question here naturally arises as to 

 whether, in the evolutionary development of the plant 



