THE PTERIDOPHYTA : FILICALES, THE FERNS 



543 



curved halves detaches a small bundle from its edge, which a little further 

 up reunites with the inner face of the same half trace. The portion between 



Fig. 543. — Botrychium lunaria. Transverse 

 section of root. 



this point of junction and the edge is then detached and passes into the 

 rachis of the fertile segment, which therefore receives two strands (Fig. 544). 

 This curious process is repeated in the sterile segment at the attachment of 

 each pair of pinnae, but each pinna receives only one strand. This anatomical 



Fig. 544. — Botrychium virginianutri. Top line of figures illustrates the origin of the double 

 trace to the fertile leaf segment. Lower line of figures illustrates the origin of the single 

 pinna traces in the sterile segment. (After Chrysler.) 



evidence strongly supports the view that the fertile segment represents the 

 two basal pinnae of the leaf, fused together. Normally these alone are 

 sporangiferous, but abnormal specimens are known in which sporangia occur 

 also on other pinnae. Primitively the leaf was probably all fertile, but the 

 reproductive organs have now become limited to the basal portion. 



