THE PTERIDOPHYTA : FILICALES, THE FERNS 



501 



once, the male and female fuse, and the oosphere secretes a wall, becoming an 

 oospore. Although several archegonia may be fertilized, only one oospore 

 in each prothallus finally comes to maturity. 



Soon after fertilization the oospore divides vertically into two, and by a 

 second and third division forms an octant or group of eight cells. Four of 

 these, directed towards the apex of the parent prothallus, form the epibasal, 

 and the other four the hypobasal hemispheres (Fig. 491). The former 



FIRST LEAF 



PROTHALLUS 



FOOT 



REMAINS OF 



NECK OF 



ARCHEGONIUM 



ROOT HAIRS 



ROOT 



Fig. 492. 



-Dryopteris filix-mas. Stages in development of the embryo after 

 emergence from the archegonium. {After Sumimki.) 



produces the axis and the first leaf of the embryo plant, the latter produces 

 the primary root and a suctorial portion called the foot, which remains 

 embedded in the archegonial venter (Fig. 492), and by which nourishment 

 is obtained until the young plant becomes self-supporting. A small, diarch 

 primary root is formed, but soon dies and is replaced by adventitious roots. 

 When the first leaf has grown large enough to nourish the young plant, the 

 prothallus usually disappears (Fig. 493). The first leaf is usually small and 

 two-lobed. The immediately subsequent leaves become larger but are also 



