FIUCALES 





to their continued exposure to moist air, or to liquid water which is 

 necessary for carrying out their function. 



The antheridium, which arises by outgrowth and segmentation of 

 a single superficial cell (Fig. 393, 2, 3), consists when mature of a 

 peripheral wall of tabular cells, surrounding a central group of sperma- 

 tocytes (Fig. 393, 4, 5). The antheridium readily matures in moist air, 



Fig. 393. 

 i, an attenuated male prothallus of Dryopteris Filix-MOS. 2 -of develop- 



ment of the antheridium. 6, 7, ruptured antheridia. 8, a spennutozoid highly 

 magnified. (After Kny.) 



but it does not open except in presence of extrrn.il water. '1 his 

 causes swelling of. the mucilaginous walls of the spermatocytes, and 

 increased turgor of the cells of the wall. The tension is relieved by 

 rupture of the wall at the distal end, and the spermatocytes are ex- 

 truded into the water; in this the remaining cells of the wall assist by 

 their swelling inwards, and consequent shortening (Fig. 393. '' • The 

 spermatocytes thus extruded into the water which caused the rupture, 



