VII PTERIDOPHYTA—FILICIME^—OPHIOGLOSSACE^ 241 



the thallus. The basal cell also divides more extensively, but 

 the group of cells derived from it is easily recognisable in the 

 ripe archegonium. 



The central cell divides transversely, the low^er cell forming 

 the Qgg, and the ventral canal cell, the upper one giving rise 

 to the single neck canal cell, w^hose nucleus later divides as in 

 Ophioglossnm. 



The mature Qgg cell contains dense cytoplasm, but has a 

 vacuole within it. Jeffrey observed a spermatozoid in the act 

 of penetrating the tgg, which showed an extension toward the 

 entering spermatozoid. The details of fertilisation, however, 



Fig. 129. — Botrychium Virginianum. Development of the archegonium, X about 450. 



were not made out, but they probably correspond closely with 

 those observed in other Ferns. "^ 



Helmin th osfachys 



The gametophyte of Helminthostachys (Lang (4)), the 



third genus of the Ophioglossaceae, does not differ essentially 



from the other genera, being also subterranean. It is nearly 



cylindrical in form (Fig. 126, C). The lower part, which is 



brown, and covered with rhizoids, is sterile, and contains an 

 16 



