174 PHENOGAMS AND CKYPTOGAMS 



on the firm soil of undisturbed pots and beds. Or spores 

 may be sown in a damp, warm place. 



321. On the under side of the prothallus two kinds 

 of organs are borne. These are the archegonium and 



the antheridium. These organs are mi- 

 nute specialized parts of the prothallus. 

 Their positions on a particular prothal- 

 lus are shown at a and 6 in Fig. 312, 



308. The brake fruits _ ,. 



underneath the revo- but in some ferns they are on separate 

 lute edges of the leaf. pro thalli (plant dioecious) . The spefm- 

 cells escape from the antheridium and in the water which 

 collects on the prothallus are carried to the archegonium, 

 where fertilization takes place. From a fertilized arche- 

 gonium a plant grows, and this plant becomes the "fern." 

 In most cases the prothallus dies soon after the fern 

 plant begins to grow. 



322. The fern plant, arising from the fertilized egg in 

 the archegonium, becomes a perennial plant, each year 

 producing spores from its fronds, as we have seen; but 

 these spores which are merely detached special kinds of 

 ce lls produce the prothallic phase of the fern plant, from 

 which new individuals 



arise. A fern is fer- 

 tilized but once in its 

 lifetime. This alterna- 

 tion of phases is called 

 the alternation of gen- 

 erations. The first or 

 fertilized plant is the 

 gametophyte ; the sec- 

 ond Or nOll - fertilized 309> Reflexed margins of a maidenhair frond. 



plant is the sporophyte (phyton is Greek for " plant " ) . 



323. The alternation of generations runs all through 

 the vegetable kingdom, although there are some groups 

 of plants in which it is very obscure or apparently want- 



