206 



VBYPTOGAMS 



be found on bare, moist earth under Ferns ; or, better, 

 in greenliouses. Tliey are attached to the soil by rhi- 

 zoids, most of wliicli spring from a modian thickening, the 

 eushion. On the under surface, mainlj^ nearer the more 

 pointed end of the jarothallium, hemispherical antlieridia 

 are borne (Fig. 350, B~). in which the spiral, ciliated 

 antJierozoids (Fig. 350, 0) liave their origin. Arcltegonia 

 (Fig. 350, A) may be found on the same prothallia, nearer 



the notched (younger) 

 extremitj'. In some spe- 

 cies, however, antheridia 

 and archegonia are always 

 home on different prothal- 

 lia ; though the spores 

 from which the two sorts 

 of prothallia arise are 

 indistinguishable. 



481. Fertilization of the 

 egg cell takes place when 

 the prothallia are wet 

 with dew or rain, by the 

 entrance of an antherozoid into the archegonium and the 

 conjugatio]i of antherozoid and egg cell. 



482. The result is the division of the egg and the for- 

 mation of an embryonic Fern plant (Fig. 351), in wliich 

 the beginnings of leaf, stem, and root 

 can soon be made out. Commonly 

 only one of the several archegonia which 

 may be fertilized gives rise to a per- 

 fected Fern plant. After the establish- 

 ment of the latter, the prothallium dies. 



483. The entire life histor}- of the 

 Fern thus comprises two stages, that 

 of the jjrothallium (bearing archegonia 

 and antheridia), and that of tlie leaf}', 351 

 spiore-bearing plant. It will be recalled 

 that in some of the lowest Algas (e.g. 

 Vaucheria) the same indi\'idual plant gives rise to spores 



A, tlie archegonium ^ith egg (e), and 

 canal (c) ; 7?, antheridium ; (', an- 

 therozoid, yei'Y highly magnihed. 

 Sthasburger. 



Prothallium with 

 young spore- 

 hearing plant. 



