206 



CRYPTOGAMS 



350 



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, ^), in which the spiral, ciliated 

 antherozoids (Fig. 350, C^ have their origin. Arcliegonia 

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



the notched (younger) 

 extremity. In some spe- 

 cies^ however, antheridia 

 and arcliegonia are always 

 home on different prothal- 

 lia ; though the spores 

 from which the two sorts 

 of prothallia arise are 

 indistinguishable. 



481. Fertilization of the 



A, the archegonium with ^g^ (e), and .. . . , , 



canal (c) ; B, antheridium ; C, an- ^&& ^^^^ tdKCS piace Wnen 

 therozoid, very highly magnified.— the prothallia are wet 



StRASBURGER. -Jl 1 • 1 ji 



With dew or ram, by the 

 entrance of an antherozoid into the archegonium and the 

 conjugation of antherozoid and Q^g cell. 



482. The result is the division of the Qgg 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 arcliegonia 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 histoiy of the 

 Fern thus comprises two stages, that 

 of the prothallium (bearing arcliegonia 

 and antheridia), and that of the leafy, 

 spore-bearing plant. It will be recalled 

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

 Vaucheria) the same individual plant gives rise to spores 



351. 



Prothallium with 

 young spore- 

 bearing plant. 



