I'TKUlDiii'IlYTES 



331 



In the ordinary Ferns all the spores in the sporangia 

 are alike, and \ylien they germinate eaeh spore iiroducos a 

 prothalliuni upon which both antheridia and arehegonia 

 appear. 



In some Pteridophytes, however, there is a decided dif- 

 ference in the size of the spores, some being quite small and 





Fig. 301. A scries showing the dehiscence of a fern siiorancrium. the niptnre of the 

 wall, the straightening and bending back of the annnliis. and the recoil.— .\fler 

 Atkinson. 



others relatiyely large, the small ones producing male game- 

 tophytes (prothallia with antheridia), and the large ones 

 female gametophytes (prothallia with arehegonia), When 

 asexual spores differ thus permanently in size, and give rise 



