VII PTERIDOPHYTA-PILICINE^—OPIIIOGLOSSACEJE 24I 



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 lower cell forming 

 the Qgg, and the ventral canal cell, the up])er one giving rise 

 to the single neck canal cell, whose nucleus later divides as in 

 Ophioglossum. 



The mature ^gg cell contains dense cytoplasm, but has a 

 vacuole within it. Jeffrey observed a spermatozoid in the act 

 of penetrating the ^gg, 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. 



Helminthostachys 



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

 third genus of the Ophioglossacese, 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 



