538 



A TEXTBOOK OF THEORETICAL BOTANY 



The Gametophyte 



The prothallus is larger and more solid than that of Dryopteris, though 

 similar to it in form. The thickened cushion may extend almost to the 

 margin. It may live for more than a year, growing and branching dichoto- 

 mously, and if unfertilized will produce adventitious branches, which grow 

 into secondary prothalli. An endophytic fungus is constantly present. 



Development of the Antheridium 



The antheridium develops from one epidermal cell which divides 

 horizontally (Fig. 537). The inner cell forms the antherozoid mother cells 



LID CELLS 



LID CELLS 



ANTHEROZOID 

 MOTHER 

 CELLS 



£^ INNER CELL 



A 



PROTHALLIAL 

 JACKET CELLS 



NECK CELLS 



NECK CANAL CELL 



VENTRAL VENTRAL 



CELL 



CANAL 

 CELLS 



OOSPHERE 



Fig. 537. — Marattia fraxitieo. Development of reproductive organs. 

 A and B, Antheridium. C and D, Archegonium. {After Goebel.) 



and the outer cell divides by vertical walls to surround a small, central, 

 triangular cell which is the operculum and is thrown off when the antheridium 

 opens. The neighbouring prothallial cells cut off segments to form a wall 

 round the mass of antherozoids. The whole antheridium is thus immersed 

 in the prothallus tissue. 



Development of the Archegonium 



The archegonium arises from one epidermal cell which divides into a row 

 of three, as in Dryopteris. The middle one forms the neck canal cell (some- 



