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STRUCTURE AND LIFE HISTORIES 



and sporophylls are very closely related to each other, 

 and demonstrate clearly that foUage-leaves may be 



Fig. 12 2— 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. 



produced by the sterilization of spore-bearing leaves. 

 The interesting question here naturally arises as to 



