LIFE HISTORY OF A FERN 



29 



being entirely so; while in other cases sporangia occur on 

 the foliage-leaf. As in the re- 

 placement of sporophylls by 

 sterile leaves in the ostrich fern, 

 Onoclea struthiopteris (para- 

 graph 8), these abnormalities 

 indicate the close relationship 

 between leaves and spore-bear- 

 ing organs, and clearly show 

 that the latter may be com- 

 pletely transformed, by sterili- 

 zation, into foliage-leaves. 



In Ophioglossum the foliage- 

 leaf and spore-bearing spike 

 are both unbranched, the latter 

 suggesting an adder's tongue, 

 whence the name, Ophioglossum. 

 In both Ophioglossum and Botry- 

 chium the sporangia originate 

 from a group of epidermal and 

 sub-epidermal cells, and are 

 consequently imbedded in the 

 surrounding tissue . Their walls 

 are more than one cell in thick- 

 ness, the annulus is lacking, and 

 they open by a slit. Ferns of 

 this type a.Te culled eusporangiate 

 {Cf. p . I o) . Their pro thallia are 

 usually fleshy and subterranean, 

 bear the antheridia and arche- 

 gonia on the dorsal instead of on 

 the ventral surface, and are per- 



FiG. 28. — Adder's tongue 

 fern {Ophioglossum vvlgatum 

 L.). B, runner or stolon. 



