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and archegonia, which are, in the main, similar to those 

 described above for the mosses, only of somewhat simpler 

 structure. The oosphere contained in the archegonium, on 

 being fertilised by one of the spermatozoids liberated by the 

 antheridia, becomes an oospore, surrounds itself with a cell 

 wall and proceeds at once by growth and cell-division to develop 

 into the young fern plant. The latter remains attached to- 

 the pro thallium by a special organ termed the foot, by means 

 of which it obtains its nourishment from the prothallium 

 until, with the development of its own leaves and roots, it 

 becomes independent and then the prothallium withers and 

 dies. The oophyte in the fern, therefore, is represented by 

 the prothallium, while the fern plant itself is the sporophyte. 

 The prothallium of the Pteridophyta is consequently homo- 

 logous with the protonema and what we call the ' ' plant ' ' of 

 the Bryophyta, while the ' ' plant ' : of the Pteridophyta is 

 homologous with the sporogonium of the Bryophyta. The 

 life history of the fern may be shortly expressed as follows : 



Sporophyte Oophyte 



Spore _ Froth allium 



d" antheridia ? archegonia 



spermatozoid = oosphere 



Fern Plant< oospore 



It should be noted that in both the Bryophyta and 

 Pteridophyta water is necessary for fertilisation, to enable the 

 spermatozoids, which swim in the w r ater, to reach the arche- 

 gonia. 



The Pteridophyta are usually sub-divided into the follow- 

 ing three groups : 



1. Ferns proper. Plants with well-developed large classification 



leaves. Sporophylls are usually similar to the of Pterido- 

 foliage leaves and are not aggregated into cone- P h y tes - 

 like structures. Each sporophyll usually bears 

 numerous sporangia. 



2. Horsetails. Plants with well-developed stems with Ferns, 



distinct nodes and internodes, more or less ribbed horsetails, 

 and with small leaves in whorls, forming a sheath 

 at each node. The small peltate sporophylls are 

 aggregated into a cone-like flower at the apex of 

 each fertile shoot. 



