206 



CRYPTOGAMS 



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

 in greenhouses. They are attached to the soil by rhi- 

 zoids, most of which spring from a median thickening, the 

 cushion. On the under surface, mainly nearer the more 

 pointed end of the prothallium, hemispherical antheridia 

 are borne (Fig. 350, J9), in which the spiral, ciliated 

 antherozoids (Fig. 350, (7) have their origin. Archegonia 

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



the notched (younger) 

 extremity. In some spe- 

 cies, however, antheridia 

 and archegonia are always 

 borne on different prothal- 

 lia ; though the spores 

 from which the two sorts 

 of prothallia arise are 

 indistinguishable . 



481. ^Fertilization of the 



350. A, the archegonium with egg (e), and _ ^ ^^ ^^ ^^ 



prothallia are wet 



canal (c) ; B, antheridium; G, an- 

 therozoid, very highly magnified. the 



with dew or rain, by the 



entrance of an antherozoid into the archegonium and the 

 conjugation 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 which 

 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 history of the 

 Fern thus comprises two stages, that 

 of the prothallium (bearing archegonia 



and antheridia), and that of the leafy, 351. prothallium with 



spore-bearing plant. It will be recalled 



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



Vaucheria) the same individual plant gives rise to spores 



young spore- 

 bearing plant. 



