l62 STRUCTURE AND LIFE HISTORIES 
produced by the sterilization of spore-bearing leaves. 
FIG. 122. Walking fern (Camptosorus rhizophyllus). 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 
