The Pteridophytes 



485 



ward, in the vicinity of the rhizoids, antheridia develop. The 

 antheridia are comparatively simple structures, with a wall 

 composed of several cells, inclos- 

 ing the sperm mother cells, each 

 of which produces a sperm. The 

 sperms have a spirally twisted 

 body and a beak with forty or 

 fifty long cilia. The archegonia 

 appear as the gametophyte ma- 

 tures, and like the antheridia 

 are located on the under side 

 near the notch, or growing re- 

 gion, of the prothallus. They 

 are simpler in structure than 

 those of Bryophytes; the neck 

 is curved, and the egg cell is 

 embedded in the prothallus. 



Fertilization. The sperms are 

 released by the swelling and bursting of the antheridium, when 

 water stands under the prothallus. Under similar conditions 

 the archegonium opens and the products of the disintegration 

 of the neck canal cells diffuse into the water. The sperms are 

 directed in their swimming by these substances, and one of the 

 sperms after entering the archegonium fuses with the egg cell, 

 forming an oospore. When fertilization has taken place in one 

 of the archegonia, the further development of the remaining 

 immature archegonia ceases. For this reason fern prothalli 

 usually produce but a single sporophyte. The same general 

 statement might also be made for the Bryophytes. 



Embryo of sporophyte. The oospore germinates directly after 

 fertilization. Cell division takes place rapidly, and an embryo 

 is soon formed that shows four general regions: (i) the foot, a 

 holdfast and absorbing region by which the embryo is attached 

 for a short time to the prothallus ; (2) a root, which rapidly elon- 



FiG. 300. Under side of a fern prothal- 

 lus, showing egg-producing organs (arche- 

 gonia) {A), the sperm-producing orgf.ns 

 (antheridia) (B), and the rhizoids (C). 



