EMBEYOGENT IN MAESILEACB^ AND FEKNS. 279 



to take place by the spermatozoids of the small spores coming into 

 contact with the large spore after the coat of the large spore has 

 burst at its apex, so as to expose the Cellular prothallium and its 

 archegonia (fig. 502 a). The free central cell of the archegonium 

 then enlarges, divides, and elongates into a filament, which grows 

 down into the prothallium (fig. ' 503). A suspensor is thus 

 formed, at the end of which is the embryo, e, imbedded in the 

 cellular tissue at the upper part of the large spore. The embryo 

 finally produces its radicle and its bud, which is developed as the 

 leafy frond. ' 



In Ehizocarps (MarsUeacese) there are also antheridia and arche- 

 gonia. The former are sacs containing small spores, which produce 

 inside a small prothallium, on which are borne antheridia contaiaing 

 spermatozoids. The latter are sporangia containing large spores 



Fig. 504. Fig. 506. Pig. 506. 



which produce a prothallium like that of Lycopods, on which 

 archegonia appear. The prothallium usually produces only one 

 central archegonium, the spermatozoids get access to the arche- 

 gonia, and thus the young plant is produced. 



In Ferns there is a prothallus bearing antheridia and archegonia 

 at the same epoch. It is produced by the spore during its gfermination, 

 and consists of cells, as shown in fig. 507. The antheridia occur 

 on the under surface of the prothallus, and they consist of a cellular 

 papilla having a central cavity (fig. 508). This cavity contains free 

 cellules, which are discharged by a rupture at the apex, b, and each 

 of these little cellules, in bursting, gives exit to a ciliated spiral 

 filament (spermatozoid), (fig. 509), which swims actively in water, 

 advancing with a rotatory motion through the water when seen under 

 the microscope. The archegonia (fig. 510) exist on the under side of 

 the prothallus, near the notch of the border. They are less numerous 

 than the antheridia (varyiiig from three to eight), and consist of 

 cellular papiUee formed by ten or twelve cells. They are larger than 



Fig. 504. The small spore of a Ehizocarp (Pil/idaria gloiulifera, PiUwort). The inner 

 coat is protruded, and the outer coat has hurst, so as to discharge cellules containing sper- 

 matozoids. Some of the spermatozoids are separate, and are seen coiled up in a spiral form. 

 Pig. 505. Large spore of a Rhizocarp {Ma/rsilea, Fepperwiyrt), which contains a cellular pro- 

 thallium hearing archegonia. The mammillary projection is the point whence the gem- 

 mation of the emhryo proceeds after impregnation. Fig. 606. Vertical section of prothal- 

 lium of a Bhizocarp {Pilularia gldbvMfe/ra), containing a central archegonium, a, hefore 

 impregnation. 



